Caribbean Paleobiology

Answer to the last post: it was a unicorn...

2011-11-28T07:02:00.000-05:00

Well, not really... at least not the horse-type of unicorn, those can only exist in the imagination of people who want to be marine biologist because they think that by doing so, they will get to train and play with dolphins at some theme park...
Anyways, the picture on the previous post seems to have been quite straightforward after all. Yes, it ispart of a narwhal tusk, so congrats to all who guessed right! Narwhals, which go by the scientific name Monodon monoceros, are odontocetes (toothedwhales), distinguished by the long spiraled tusk seen in themales (and occasionally females) of the species, and are thus sometimes called the "unicorn of the sea".

Dorsal view of a double-tusked narwhal, on exhibit at the Sant Ocean Hall at the National Museum of Natural History in Washington, DC. Normally, narwhals only have one enlarged tusk (the left one) so this one is an exception.

The closest relatives of the narwhals are the belugas or white whales (Delphinapterusleucas); together these two speciescomprise the family known as Monodontidae. Among extant toothed whale groups,monodontids are more closely related to porpoises (Phocoenidae) and to dolphins(Delphinidae) (e.g. see Geisler etal., 2011), whereas relationships with extinct groups include Albireonidae(Barnes, 1984) and Odobenocetopsidae (de Muizon, 1993). Odobenocetops previously featured here,also has an enlarged tusk-like tooth like Monodon. However, the tusks are located in different boneswithin the rostrum (the premaxilla in Odobenocetops, the maxilla in Monodon [see below]), and hence although somewhat similar, they are probably nothomologous.

Ventral view of the rostrum of extant monodontids.

The fossil record of monodontids, is scarce (atleast when compared to that of other living odontocete groups). The oldest monodontidknown is Denebola brachycephala from thelate Miocene of Baja California (Barnes, 1984). Other fossil monodontids are known from earlyPliocene deposits in the North Sea (Lambertand Gigase, 2007) and the eastern coast of North America (Withmore, 1994;Withmore and Kaltenbach, 2008; Kazár and Bohaska, 2008)*. All these fossilforms are more like Delphinapterus,i.e. they have multiple teeth in the maxilla, whereas Monodon only has an enlarged tusk (usually only in the male) and the females is edentulous (see illustration above). So how did the tusk of narwhals came to be or what is it for? It isstill a bit of a mystery!

*I'll blog more on these North American ones sometime next year, so stay tuned!

For a neat article on the tusk and on monodontids visit thispage over at Tetrapod Zoology v2.
And here if you or someone you know wants to be a marine biologist.

References:

Barnes, L. G. 1984. Fossil odontocetes (Mammalia: Cetacea)from the Almejas Formation, Isla Cedros, Mexico. PaleoBios 42:1–46.

Geisler, J. H., M. R. McGowan, G. Yang and J. Gatesy. 2011.A supermatrix analysis of genomic, morphological, and paleontological data fromcrown Cetacea. BMC Evolutionary Biology 11:112.

Kazár, E., and D. J. Bohaska. 2008. Toothed whale (Mammalia:Cetacea: Odontoceti) limb bones of the Lee Creek Mine, North Carolina; pp.271-324 in C. E. Ray, D. J. Bohaska, I. A. Koretsky, L. W. Ward, and L. G.Barnes (eds.), Geology and Paleontology of the Lee Creek Mine, North Carolina,IV. Virginia Museum of Natural History Special Publication 14.

Lambert, O., and P. Gigase. 2007. A monodontid cetacean fromthe Early Pliocene of the North Sea. Bulletin de l’Institut Royal des SciencesNaturelles de Belgique, Sciences de la Terre 77:197–210.

Muizon, C. de. 1993. Walrus-like feeding adaptation in a newcetacean from the Pliocene of Peru. Nature 365:745–748.

Whitmore, F. C., Jr. 1994. Neogene climatic change and theemergence of the modern whale fauna of the North Atlantic Ocean. Proceedings ofthe San Diego Society of Natural History 29:223–227.

Whitmore, F. C., Jr., and J. A. Kaltenbach.2008. Neogene Cetacea of the Lee Creek Phosphate Mine, North Carolina; pp.181–269 in C. E. Ray, D. J. Bohaska, I. A. Koretsky, L. W. Ward, and L. G.Barnes (eds.), Geology and Paleontology of the Lee Creek Mine, North Carolina,IV. Virginia Museum of Natural History Special Publication 14.

What is this?

2011-11-07T09:59:00.000-05:00

This might be an easy guess for some of you or maybe not... Let me know what you think in the comments section. I'll be back with the answer in a week or so. Enjoy!

Bad weather, ancient oceans and modern seagrasses… a brief visit to Puerto Rico

2011-09-03T21:26:00.000-04:00

Summertime is normally when geologist and paleontologistengage in fieldwork. For me the last two summers have been different;I’ve spent both teaching in the human anatomy lab at USUHS, which has been a fantastic experience. However, being busy in the summer months hasn’t really stopped me from doing a little fieldwork, fortunately, I workmostly in the Caribbean region where the weather is generally nice and the onlything to worry about is hurricane season…

And so it was that I had the chance to go to Puerto Rico at the end of the summer and inthe midst of hurricane season. Every time I go there is both for pleasure andwork; I get to see my family, enjoy the food and scenery and with a healthydose of fieldwork, it makes for the perfect vacation. This time I arrived twodays before hurricane Irene (then still a tropical storm) hit the island. I wasfortunate to be staying in the northwestern part of the island, which did muchbetter than most other parts. We got rain, lots and lots of it, which kind ofmessed up my plans for fieldwork a little bit.

Meanwhile, while it rained, I stayed busy looking throughfossils I had collected during my years as an undergrad; mostly fish teeth(bony and cartilaginous) and otoliths,which I’ll use for some projects on the works. It wasn’t until ~~five~~ six,days after my arrival that it was sunny and dry enough to go out to the field.Without much time to go to different places, I decided that my best chancesfor fieldwork were in the vicinity of my hometown, basically hereand here.

The early Oligocene "mystery" bone I found.

So first I went to the Río G locality where early Oligocenedeposits are exposed along the banks of the river. Its one of my favorites andalmost always I find something of interest. With all the rain, I was bothworried and hopeful. Worried that cool stuff was being eroded away, but hopefulin that new stuff would be exposed. After prospecting for a while and notfinding anything more than some sirenian ribs, I made it to the “bonebed”(previously featured here).This time around all that I found was an interesting piece of bone (see pictureabove), and as it turned out, I had good reasons be worried. If you look at thepicture, the part of the bone towards the bottom had broken off, recently,probably during the rain and increased water levels earlier in the week. Itdoesn’t seem to be a rib, which is why I think its interesting, but due to itsincompleteness I’m still not sure what it is… it sounds a bit frustrating, butthe best thing to do is to turn that frustration into motivation to keeplooking!

My favorite beach in the Atlantic coast of Puerto Rico. Just how I like it, early in the morning and nearly devoid of people.

My other field excursion was to the beach. Working withmarine organisms that thrive in shallow marine environments is always a goodexcuse for a trip to the beach (specially in the tropics). Staying in myhometown meant that my favorite beach on the Atlantic coast of Puerto Rico wasonly a 15-minute drive away! I didn’t see any manatee (wasn’t expecting toanyways) but did get to see some seagrass beds (see picture below).

It was wavy and shallow (~1m) hence all the suspendedsediment. The turtle grass blades (leaves) are about 0.5-1 cm wide and ~10-12cm long.

Most seagrass beds in the Western Atlantic and Caribbeanregion consist of several species, with Thalassia testudinum (turtle grass), Halodule beaudettei (shoal grass), and Syringodium filiforme (manatee grass) as the more commonones. However, the seagrass bed that I was looking at was monospecific (= only one species present). As far as I could tell it consisted solely of turtle grass.Monospecific beds of turtle grass are not uncommon, in fact, Thalassia is what is known as a climax species. Thatmeans that it is the dominant species of seagrass; other species (like the onesmentioned above) are only present in small, disturbed patches or at theperiphery of the beds. The dominance of turtle grass over other seagrassspecies and its consequences (like mass die-offs) in historical times has beenpartly blamed on overkill of large marine herbivores, mainly seacows and greenturtles (Jackson et al., 2001). However, this could be slightly different whenviewed from a deeper historical perspective. I hope to bring more on thissometime in the upcoming months…

Jackson, J. B. C. et al. 2001 Historical overfishing and the recent collapse of coastal

ecosystem. Science 293,629-638.

The hand of Steller’s sea cow, revisited

2011-06-15T13:22:00.003-04:00

It’s been quite a while since my last post. A lot has been going on, mostly research-related, which is good. Just last week I was in San Diego where I participated in the Sixth Triennial Conference of Secondary Adaptation of Tetrapods to Life in Water held at San Diego State University. The meeting was a great opportunity to see colleagues as well as making new acquaintances, hat tip to the host committee: Annalisa Berta, Tom Deméré and Eric Ekdale for such a great meeting! The week before that I spent some days visiting the collection at the Natural History Museum of Los Angeles where I got to look at some interesting sirenian and cetaceans, many thanks to Larry Barnes and Sam McLeod for access to specimens.

Ok, so now to the meaty part of this post. Back in 2008 I wrote about the hand of Steller’s sea cow (Hydrodamalis gigas) or more likely the lack of one. Back then I mentioned that G. W. Steller was one of the few people who saw H. gigas alive, and in his account he mentions the lack of fingers in this species. However, so far no hand bones have been found associated with Hydrodamalis gigas or even H. cuestae (see reconstruction below) (the presumed direct ancestor of the former), this lead to skepticism about his observations. So, how was that Steller’s account about the hand of H. gigas was corroborated?

Hydrodamalis cuestae, in left lateral view (picture of the reconstruction on exhibit at the San Diego Natural History Museum). Notice the reduced forelimbs.

The discovery of Dusisiren dewana in the Late Miocene (10-8 million years ago [mya]) of Japan, provided the key elements to support Steller’s account. Dusisiren is a genus of sea cow that include two other, earlier species: D. reinharti from the Early Miocene (20-16 mya) and D. jordani from the Middle-Late Miocene (12-10 mya) (see picture of D. jordani below). The species of Dusisiren together with Hydrodamalis cuestae (see picture above), H. spissa and H. gigas are members of a subfamily of dugongids (which means they are more closely related to dugongs than to manatees) known as the Hydrodamalinae (Domning, 1994; Domning & Furusawa, 1994). Hydrodamalines, as they are also known, ranged throughout coastal waters of the northern Pacific, from Baja California to Japan, with one species surviving until historical times (Domning & Furusawa, 1994). Some distinctive features of this group include, large body size, reduction or loss of dentition, and reduction of the digits, which brings us back to D. dewana.

Dusisiren jordani, anterior view (specimen at exhibit at the Natural History Museum of Los Angeles). Notice the "normal" hand in this species.

Described by Takahashi et al. in 1986, the remains of Dusisiren dewana were found in Late Miocene deposits in Japan and together with other elements of the skeleton there was also a nearly complete forelimb, including the hand. These were crucial in providing an insight into what the hand of later hydrodamalines was like. Dusisiren dewana shows reduction of the hand bones, in this respect differing from D. jordani, its predecessor, whose hands showed no reduction of elements (i.e. long metacarpals and long fingers composed of multiple elements) (see picture above). As for D. dewana, the carpals (wrist bones) are quite similar to those of other sirenians, however, the metacarpals (the bones between the wrist and fingers) and the phalanges (finger bones) are reduced, actually extremely reduced in the case of the phalanges (see picture below of Hydrodamalis cuestae). D. dewana as the sister taxon (closest relative/ancestor) of Hydrodamalis spp. is best evidence at hand (unintended pun) supporting Steller’s account on the hand of the sea cow that bears his name and allowing for reconstructions like the one seen here for H. cuestae.

Hydrodamalis cuestae, right lateral view (picture of specimen on exhibit at the San Diego Natural History Museum). Notice the reduced hand.

Domning, D. P. 1994. A phylogenetic analysis of the Sirenia. Proceedings of the San Diego Society of Natural History 29:177-189.

Domning, D. P. & H. Furusawa. 1994. Summary of taxa and distribution of Sirenia in the North Pacific Ocean. Island Arc 3:506-512.

Takahashi, D., D. P. Domning & T. Saito. 1986. Dusisiren dewana, n. sp. (Mammalia: Sirenia), a new ancestor of Steller’s sea cow from the upper Miocene of Yamagata Prefecture, northeastern Japan. Transactions and Proceedings of the Paleontological Society of Japan, New Series 141:296-321.

When you're strange, or how different are the teeth of extant sirenians

2011-03-05T15:19:00.004-05:00

Living sirenians (sea cows: manatees and dugongs) are but the remnants of a much more diverse group whose history extends back at least to the late Early Eocene (~50 million years ago [Ma]). There are only four living species of sirenians: the manatees (grouped in the family Trichechidae) and including three species: the Antillean manatee (Trichechus manatus)*, the Amazonian manatee (T. inunguis) and West African manatee (T. senegalensis). The other extant species is the dugong (Dugong dugon) that, together with the now extinct Steller’s sea cow (Hydrodamalis gigas), represents the family Dugongidae.

*T. manatus includes two subspecies: the West Indian manatee (T. manatus manatus) and the Florida manatee (T. manatus latirostris).
Above, Homo sapiens and Trichechus manatus latirostris. (Pic. courtesy of B. Bonde).

Although overall very similar to their extinct relatives, some characteristics of these extant sirenians are quite different and unique, not really representative of each particular group. One of those characteristics, and the one I will discuss here, is the dentition of Dugong dugon. This species, which lives in the Indo-Pacific region, is characterized by having molars that are best described as nearly enamel-less (a thin enamel cap is quickly worn off), open-rooted, ever-growing pegs (see pictures below), resembling more those of sloths, than those of manatees!!

Lower molars of Dugong dugon, notice that root and crown are continuous. The dark area is the part that was exposed above the gum line, hence the staining.
To understand how they differ let me give you a little background info on sirenian dentition. Primitively, the dental formula of sirenians consisted of three incisors, one canine, five premolars* and three molars (Domning, 1994; Savage et al., 1994). Throughout sirenian evolution, this formula has been reduced, first by loss of the fifth permanent premolar in the earliest dugongids (see figure below), then by subsequent loss of second and third incisors, canine and the other permanent premolars. In terms of general features, the molars of most fossil sirenians can be described as bilophodont, with enameled crowns that are clearly differentiated from the root (these being closed and multiple [with three in upper molars and two in the lowers]). These kind of molars somewhat resemble those of the most primitive proboscideans (Sanders et al., 2010), which, by the way, are the closest relatives of sirenians.

*Presence of a fifth premolar is reminiscent of the primitive eutherian condition and, among Cenozoic placental mammals, a pretty unique condition only seen in sirenians (Rose, 2006).

Partial left maxilla of a Late Eocene (37.2-33.9 Ma) dugongid, (A) lateral view (reversed); (B) occlusal view (anterior to the right). Notice that the deciduous premolar is molarized and multi-rooted, whereas the permanent premolars are more conical and single rooted. dP = deciduous premolar; M = molar; P premolar (permanent).

Beginning about the Early Oligocene (33.9-28.4 Ma) the dental formula of most dugongids (including Dugong) stayed the same; it consisted of the first upper incisor, upper and lower deciduous premolars 3-5 and permanent molars 1-3 (see A-B in figure below)* (Domning & Pervesler, 2001). Up until the appearance of Dugong dugon the morphology of the molars was, in general, much the same as that described above. The peculiar, somewhat aberrant, dentition of dugong likely evolved quite recently (geologically speaking). Unfortunately there are no fossils of D. dugon to really know when. The best evidence comes from a very Dugong-like sirenian skull from the Pleistocene of Florida (Domning, 2001) (sadly, it is in a private collection). This skull is from sediments that were deposited about two million years ago and is nearly identical to Dugong dugon; one of the few differences, actually the most obvious one, is that its teeth are much like those of earlier dugongids, bilophodont, with enamel and multiple, closed roots. Therefore, if this fossil is taken as the closest ancestor of extant dugong, it would imply that its bizarre dentition is a quite recent (less than 2 million years) evolutionary novelty.

*Or even further reduced from that condition (as was the case of Steller’s sea cow and its closest relatives).

Occusal view of various sirenians (A-C). A. Left upper toothrow of a Late Oligocene (28.4-23 Ma) dugongid from Puerto Rico. B. Right lower toothrow of Dugong dugon, notice that the lack of enamel, leaves a nearly featureless surface; the black rim is just stain on the portion of the tooth that was above the gum line. C. Left upper toothrow of Trichechus inunguis.

Manatees (Trichechus spp.) also have unusual dentition when compared to dugongids and some of their ancestors (for starters they lack incisors). If you look at the figure above (C) you’ll notice that there seems to be more molars than there should be. And that is correct; manatees have supernumerary molars that are constantly being replaced throughout their entire life (not to be confused with the delayed eruption that characterizes elephants). The molars in Trichechus are also proportionately small, that way more can fit in the toothrow at a given time (sometimes up to eight! [Domning & Hayek, 1984]). The earliest evidence for supernumerary molars in trichechids is seen in Ribodon limbatus, a fossil manatee from the Late Miocene (11.6-5.3 Ma) or Early Pliocene (5.3-3.6 Ma) of Argentina (Ameghino, 1883; Pascual, 1953; Domning, 1982). Ribodon does differ in that its molars were not reduced, so there were less per toothrow. Other fossil trichechids have the more “normal” type of molars described above.

Anyways there you have it; extant seacows have quite different dentition from their extinct relatives. Of course, there remains the questions of why evolve ever-growing molars, or ever-replacing supernumerary molars. But I’ll leave those for some other occasion.

Ameghino, F. 1883. Sobre una colección de mamíferos fósiles del piso mesopotámico de la formación patagónica, recogidos en las barrancas del Paraná por el professor Pedro Scalabrini. Boletín de la Academia Nacional de las Ciencias de Córdoba 5:101-116.

Domning, D. P. 1982. Evolution of manatees: a speculative history. Journal of Paleontology 56:599-619.

Domning, D. P. 1994. A phylogenetic analysis of the Sirenia. Proceedings of the San Diego Society of Natural History 29:177-189.

Domning, D. P. 2001. Sirenians, seagrasses, and Cenozoic ecological change in the Caribbean. Palaeogeography, Palaeoclimatology, Palaeoecology 166:27-50.

Domning, D. P. & L.-A. C. Hayek. 1984. Horizontal tooth replacement in the Amazonian manatee (Trichechus inunguis). Mammalia 48:107-127.
Domning, D. P. & P. Pervesler. 2001. The osteology and relationships of Metaxytherium krahuletzi Depéret, 1895 (Mammalia: Sirenia). Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft 553:1-89.

Pascual, R. 1953. Sobre nuevos restos de sirénidos del mesopotamiense. Revista de la Asociación Geológica de Argentina 8:163-181.

Rose, K. D. 2006. The Beginning of the Age of Mammals. John Hopkins University Press, Baltimore, Maryland, 428 pp.

Sanders, W. J., E. Gheerbrant, J. M. Harris, H. Saegusa & C. Delmer. 2010. Proboscidea; pp. 161-251 in L. Werdelin & W. J. Sanders (eds.), Cenozoic mammals of Africa. University of California Press, Berkeley, California.

Savage, R. J. G., D. P. Domning & J. G. M. Thewissen. 1994. Fossil Sirenia of the West Atlantic and Caribbean region. V. The most primitive known sirenian, Prorastomus sirenoides Owe, 1855. Journal of Vertebrate Paleontology 14:427-449.

Dominican Republic, part II

2010-12-02T13:13:00.006-05:00

Hello there dear readers. Today I bring you the second installment of this series. Like I mentioned in the previous post we moved from the Albian to the Miocene.

The Miocene of the Dominican Republic is probably best known for the amber deposits. These have not only produced beautiful amber, which is used in jewelry, but also a number of fossil taxa have been described based on remains entombed in the amber. These fossils consist mostly of invertebrates, however, several vertebrates have been described as well, including anoles, frogs, and an insectivore. This gives us a glimpse into the smaller fauna that inhabited the island during the Miocene, in contrast to what is known from the same age in Puerto Rico and Cuba where most of the vertebrate fossils of that age consist of larger animals (sloths, rodents, primates, sirenians, crocodylians and turtles). A good summary of the vertebrates known from the Tertiary of the Greater Antilles can be found in table 1 of MacPhee et al. (2003) (free download here).

One of our first excursions into the Miocene was on a Wednesday afternoon. We spent the morning collecting the last samples from one of the outcrops of the Hatillo Limestone and some rudists from near the entrance of a cave in that same limestone unit. We then headed west towards the Monte Plata Province where we knew there was a new road cut exposing units of Miocene age.

The first outcrop of the Miocene that we visited. This is actually one of the best Miocene outcrops I've seen in a while.

By the time we got there it was near the middle of the afternoon, which meant we didn’t had much sunlight left. We stopped in the first large outcrop we saw (Picture above) and it was worth it! We quickly started finding turtle shell fragments, and occasionally we saw cross sections of turtle shells that went into the outcrop. I decided to collect one of these. It was not big, and as I found out after prep work, not too good (see pictures below). However, it was worth going there, as there is more material to be found and collected!

Top left: me overturning the jacket with the turtle shell remains; top right: the jacket back in the lab; bottom left: view of the jacket when it was first opened; bottom right: the fossil turtle remains. (Click on the image to see the larger version.)

Several days latter we had some free time, so we decided to go back to this area. This time we drove in from the north, driving through Los Haitises where we saw beautiful karst topography. Our time was limited in this occasion as well, but we made the most out of it.

The second outcrop we visited, smaller than the first one, but still interesting. Alvin Bonilla for scale.

We hit a couple of outcrops (Picture above) where we found the usual (at least what usual for the Tertiary of Puerto Rico and Cuba); croc teeth, turtle shells and sirenians (which was what I was really after). The sirenian material was in a concretion, half of it which had fallen off the outcrop so it made it easy to collect. The other part is still in the outcrop and I hope to go back sometime in the spring to collect it. Actually, if it wasn't for Alvin, who saw it, I almost stepped on the part that had fallen trying to get a better view of the part still in the outcrop. After some prep work on the sirenian material it turned out to be mostly ribs, and a few vertebrae. However, even if it is a little frustrating, it will nonetheless be an important contribution to the understating of sirenian distribution during the Miocene of the Caribbean and demonstrates that there is probably more, better material waiting to be collected!

Top left: me collecting the concretion with the sirenian remains; top right: view of the jacket in the lab; bottom left: the jacket, recently opened; bottom right: the concretion, as of now, still need some prep work to be done. Oysters (near the center of the concretion and to the right) used some of the ribs as hardground. (Click on the image to see the larger version.)

MacPhee, R. D. E., M. A. Iturralde-Vinent & E. S. Gaffney. 2003. Domo de Zaza, an Early Miocene vertebrate locality in south-central Cuba, with notes on the tectonic evolution of Puerto Rico and the Mona Passage. American Museum Novitates 3394:1-42.

Dominican Republic, part I

2010-11-02T19:42:00.004-04:00

It’s been quite a while since I posted something here as I’ve been very busy since the last post, which you should check out, if you haven’t! The absence was mostly because I’ve been distracted with university-related stuff, work (I had a real job over the summer), meetings and a month-long fieldtrip to the Dominican Republic, which will be the subject of this and the following entries.

Top: on our way to Bonao. Bottom: some of the beautiful rice field near Bonao. (Click on the picture to see the larger version.)

To begin with, I had never been to the Dominican Republic before; it was actually my first time in another Caribbean island other than my own, Puerto Rico. I did not know what to expect, but I ended up with a very good impression of the island and its people! There were many things I liked, for example, there seems to be a lot of land dedicated to agriculture (which I think is awesome), the food was delicious and of course, the geology is very interesting!!

The focus of the trip to the DR was to collect rock samples and fossils from Early Cretaceous limestones as part of the thesis project of my friend and colleague Alvin Bonilla-Rodriguez from the Geology Department at the University of Kansas. Our collecting efforts were mainly focused in the central part of the country where Albian-age limestones occur. We stayed most of the time near the towns of Bonao in the Monseñor Nouel Province and in Hato Mayor del Rey in Hato Mayor Province. Other people that joined us during our time there were: Luis Gonzalez from the Department of Geology at the University of Kansas (and Alvin’s advisor) and Wilson Ramírez and Hernán Santos from the Department of Geology at the University of Puerto Rico-Mayagüez. The Servicio Geológico Nacional and its director Santiago Muñoz Tapia were also very helpful in terms of logistics and advise.

At first it was hard finding good outcrops, some were heavily overgrown and in other occasions our compact car was obviously ill-fitted for some of the roads we needed to go through. But, by about the middle of our first week we finally found some outcrops, not the best, but it was a start!

Top: our first official stop, near the southeast corner of Presa Hatillo, the outcrop was completely overgrown. You can see Alvin (left), Luis (right) and Wilson (background), and our (very) compact cars. Bottom: one of the road we manage to get our car trough, there were others which were definitely impassable by our vehicle. (Click on the picture to see the larger version.)

Our luck got better when we moved east towards Hato Mayor. There we found a very nice outcrop (with lots of fossils) of the Hatillo Limestone! The fossils were very important, specially the rudist, for determining the age of the rocks. And yes, we were in the Albian!

Top left: our first outcrop, yes there is an outcrop in there! Top right: the nice outcrop of the Hatillo Ls is in the top of that hill. Bottom left: Coalcomana ramosa, a rudist, finding this particular species meant we were in the Albian. Bottom right: Hernán (left) and Alvin (right) collect rock samples from the Hatillo Ls. (Click on the picture to see the larger version.)

Well, this is it for this first post. Remember there are more to come, so stick around! On the next post we’ll move from the Albian, to the Miocene!

Convergencia: el caso de Odobenocetops ó el delfín que parecía morsa

2010-07-18T08:37:00.009-04:00

Convergencia; en biología y paleobiología, se utiliza este término para referirse a instancias donde dos (o más) organismos, de grupos no relacionados, poseen rasgos morfológicos similares los cuales sirven un mismo propósito. Estas similitudes se pueden clasificar como homólogas (aquellas que están compuestas por estructuras similares, como las alas de las aves y las de los murciélagos) o análogas (aquellas que han evolucionado de estructuras distintas, como las alas de las aves y las de una mariposa). Otro ejemplo de convergencia se ve en los mamíferos con dientes hipsodontes. Caballos, algunos roedores y los desmostilios* tienen (o tenían) dientes hipsodontes. Este tipo de diente tiene coronas muy altas, por ende tardan más en desgastarse; esta morfología se correlaciona con dietas abrasivas (como comer grama o comer en lugares donde hay mucho sedimento mezclado con el alimento). Si estos organismos no tuvieran este tipo de dientes sería contraproducente continuar con ese modo de alimentación ya que sus dientes se gastarían muy rápido. Así que la selección natural ha favorecido tener dientes hipsodontes en estos organismos que llevan una dieta que incluye material abrasivo.

*Información adicional sobre desmostilios, incluyendo reconstrucciones, aquí, aquí y aquí.

En organismos vivos es relativamente fácil determinar si estructuras parecidas son convergentes o no, ya que se pueden hacer observaciones directas sobre el comportamiento o función de la estructuras o morfología que se consideran convergentes. Sin embargo, con los fósiles es distinto ya que generalmente no podemos hacer observaciones directas sobre el comportamiento de un organismo extinto. Es por esto que nos toca entonces interpretar la funcionalidad de esas estructuras comparando con lo que conocemos de organismos vivos. A continuación les traigo un interesante ejemplo de convergencia entre un fósil y un organismo moderno

Odobenocetops

En el 1993, Christian de Muizon describió un fósil de delfínido (el grupo de ballenas que incluye a los delfines) que representa uno de los mejores ejemplos de convergencia que conozco. El fósil consistía en parte de un cráneo (ver la imágen abajo) colectado en el sur de Perú. Los sedimentos donde se encontró el fósil son parte de una secuencia de rocas sedimentarias conocida como la Formación Pisco, de edad Pliocénico Temprano (5.3-3.6 millones de años). El fósil no solo representaba una nueva especie, sino también un nuevo grupo de delfínidos al cual llamó Odobenocetopsidae.

El primer espécimen descrito lo llamaron Odobenocetops peruvianus Muizon, 1993 (ver imagen abajo). Los rasgos morfológicos más distintivos de esta especie consisten en tener el rostro corto (el área frente a los ojos), procesos alveolares de la premaxilla (los espacios para los dientes) agrandados y orientados hacia abajo; los procesos alveolares era donde tenían unos colmillos también agrandados. La premaxilla también tiene varios forámenes y áreas de inserción de músculos bien marcadas que indican la presencia de labios grandes y quizás hasta bigotes. Otras características del cráneo incluye tener las órbitas de los ojos posicionadas dorsalmente y un paladar profundo. Estas características que tanto distinguen a los odobenocetópsidos son reminiscentes a las morsas* más que a otros delfinoideos.

*Vean las imágenes de un cráneo de morsa y comparen.

Odobenocetops peruvianus, arriba, foto del cráneo en vista lateral (anterior hacia la derecha); abajo, ilustración del cráneo mostrando los diferentes huesos que lo componen y el área de la órbita (cículo azul), modificada de Muizon (1993). Abreviaciones: Al = aliesfenoide; Bo = basioccipital; Fr = frontal; Mx = maxila; Na = nasal; Oc = occipital; Or = órbita; Pa = parietal; Pal = palatino; Pmx = premaxila; Ppo = proceso postorbital; Ppr = proceso preorbital; Pt = terigoide; Z = zigomático.

Otra especie adicional fue descrita unos años más tarde (Muizon et al., 1999). Odobenocetops leptodon también fue encontrado en la Formación Pisco, sin embargo, proviene de un horizonte alrededor de un millón de años más joven que donde se encontró O. peruvianus. Algunas de las características que distinguen a esta nueva especie es un rostro más grande y redondeado, mayor tamaño del paladar y la presencia de fosas (depresiones) para los sacos premaxilares. La ocurrencia de esta última estructura que menciono, se correlaciona con la presencia del órgano del melón (Mead, 1975), la cual es una estructura utilizada para ecolocalización. O. peruvianus aparentemente carecía de esta estructura ya que carece de fosas para los sacos premaxilares, sin embargo, la posición de las órbitas y la forma de los procesos supraorbitales le permitía tener visión binocular; en O. leptodon los procesos supraorbitales eran distintos y sus orbitas estaban posicionadas más hacia el lado, careciendo de visión binocular, pero al menos auxiliado por la presencia del órgano del melón y la capacidad de hacer ecolocalización. Así que al parecer, O. peruvianus dependía de la visión para localizar su alimento, mientras que O. leptodon probablemente dependía mayormente de ecolocalización (como es el caso de muchos otros delfinoideos).

Los odobenocetópsidos están relacionados al único otro grupo de cetáceos que tienen colmillos agrandados, los narvales. Estos también tienen un colmillo agrandado (y en ocasiones los dos), pero estos están orientados hacia adelante. En los odobenocetópsidos la función de estos colmillos parece haber sido social ya que presentan dimorfismo sexual; los machos poseen un colmillo (el de la derecha) más agrandado que el otro (algunos hasta midiendo más de un metro), mientras que en las hembras ambos eran más pequeños y similares en tamaño (Muizon et al., 1999; Muizon & Domning, 2002).

Reconstrucción de Odobenocetops ilustración de Mary Parrish (National Museum of Natural History, Washingon, DC), tomado de Muizon et al. (1999).

¿Que pudo llevar a un delfínido a parecer una morsa?

El parecido de los odobenocetópsidos a las morsas (convergencia) llevó a los paleontólogos que los han estudiado a inferir que su modo de alimentación era muy similar. O sea, que posiblemente, al igual que las morsas, los odobenocetópsidos se alimentaban de bivalvos bentónicos (que viven en el suelo marino), localizándolos con asistencia de los bigotes, aguantando el bivalvo con los labios y utilizando la lengua como un pistón, creando un vacío dentro de la cavidad bucal para lograr succionar el organismo fuera de su concha.

La distribución geográfica de las morsas, tanto vivas como las fósiles, está limitada al hemisferio norte (Deméré et al., 2003). Asumiendo que las especies extintas de morsas tenían las mismas preferencias alimenticias que la especie moderna (y al parecer así era) y al tener una distribución limitada, ese espacio ecológico, ocupado por las morsas en el hemisferio norte, estuvo “vacío” en el sur. Es así que posiblemente surgió este caso de convergencia, donde un delfinoideo termina pareciendo una morsa, ocupando ese espacio ecológico y utilizando los recursos disponibles.

Este es uno de los casos en paleontología donde el presente es la llave del pasado. Si no conocieramos las morsas habría sido muy difícil interpretar la funcionalidad morfológica de estos extraños delfinoideos.

Deméré, T. A., A. Berta & P. J. Adam. 2003. Pinnipedimorph evolutionary biogeography. Bulletin of the American Museum of Natural History 13 (279):32-76.

Mead, J. G. 1975. Anatomy of the external nasal pasajes and facial complex in the Delphinidae (Mammalia, Cetacea). Smithsonian Contributions to Zoology 207:1-72.

Muizon, C. de. 1993. Walrus-like feeding adaptation in a new cetacean from the Pliocene of Peru. Nature 365:745-748.

Muizon, C. de & D. P. Domning. 2002. The anatomy of Odobenocetops (Delphinoidea, Mammalia), the walrus-like dolphin from the Pliocene of Peru and its paleobiological implications. Zoological Journal of the Linnean Society 134:423-452.

Muizon, C. de, D. P. Domning & M. Parrish. 1999. Dimorphic tusas and adaptive strategies in a new species of walrus-like dolphin (Odobenocetopsidae) from the Pliocene of Peru. Comptes-rendus de l’Academie des Sciences, Paris, Sciences de la Terre et des Planetes 329:449-455.

Better late than never: GSA 2009

2010-07-11T13:06:00.004-04:00

This has been a particularly long hiatus, and not because I wanted to, but it has been a particularly busy summer.

Anyways, if you missed my poster presentation at the 2009 annual meeting of the Geological Society of America, here is your chance to see it. Below is the abstract (you can also see it here) as well as the poster itself.

Evolution and diversification of Dugonginae (Sirenia: Dugongidae) in the West Atlantic and Caribbean region

Jorge Velez-Juarbe & Daryl P. Domning

Sirenian evolution presumably started in the southern Tethys realm of the Old World. However, the most primitive sirenians have been found in the Caribbean region in rocks that date back to the Early or Middle Eocene, evidence that they took on an aquatic lifestyle early in their history and were able to disperse around the Atlantic. Since then, the West Atlantic and Caribbean (WAC) region has been important for the evolution of this group of mammals, with all four of the known families (Prorastomidae, Protosirenidae, Dugongidae, Trichechidae) occurring in the region. From the Oligocene through Pliocene, the predominant groups in the WAC region were members of the dugongid subfamilies Dugonginae and Halitheriinae, with the former being the more speciose of the two. In some parts of the WAC, dugongines and halitheriines are found in the same deposits, indicating that some form of niche partitioning was occurring among three or even more sympatric species of sirenians, something that is not observed among the living species.

Niche partitioning among sympatric sirenian species is most obviously explained by differences in: (1) tusk morphology; (2) rostral deflection; and (3) body size. The most primitive members of the Dugonginae are found in the WAC region. Their distinctive cranial morphology seems to have evolved as a specialization for harvesting larger seagrass rhizomes that were out of reach of the less specialized halitheriines. New fossils from Puerto Rico, Florida, and Yucatán help to reinforce our ideas about niche partitioning among sympatric sirenian species as well as establish the WAC region as the center of known dugongine diversity.

This was my first poster presentation about one of the topics that I’m working on as part of my thesis. The poster was a success! I was awarded runner-up of the 2009 Paleontological Society Poster Award. Congratulations to the first place and to the other runner-up too! It was a great meeting with very interesting talks as well as getting to spend some time with good friends!!

Enjoy the poster and feel free to ask question or make comments!

Answer to the last post

2010-04-19T15:40:00.003-04:00

Ok, so while I slowly prepare a more lengthy post. Here’s the answer from last post. The skull I showed last time is that of a species of Metaxytherium, exactly which one, well, I’ll talk about that in the future. That skull is from Early Oligocene deposits, therefore it is several million years older than other reported species of Metaxytherium.

Here’s the skull in lateral and dorsal views. (Notice that part of the rostrum is missing.)

It is somewhat similar to M. crataegense (=M. calvertense [Aranda-Manteca et al., 1994]) from the Early Miocene of the Western Atlantic and Caribbean, as well as to other species of Metaxytherium, but, it also displays plesiomorphic conditions not seen in those other species.

Another possibility would be Caribosiren turneri (drawing above modified from Reinhart, 1959), from the Early Oligocene of Puerto Rico. But, unlike Caribosiren the rostrum of this critter doesn’t seem to have been as extremely downturned; also it belonged to an animal at least 15% larger than Caribosiren. Other Oligocene halitheriines such as Halitherium schinzii from the European Early Oligocene, have different morphology of the parietal as well as much larger nasals; Eosiren imenti, known from the Early Oligocene of Egypt (Domning et al., 1994), is even more primitive than Halitherium schinzii, as it still has permanents premolars and canines, among other characteristics.

So, as far as I can tell, it seems to be a primitive Metaxytherium. There are other skulls from Early or Late Oligocene of the western Atlantic, which are very similar to this one, possibly the same species, that’s one thing I have to figure out as part of my thesis. If you’re going to the SVP meeting this year, you might learn more about this critter.

Aranda-Manteca, F. J., D. P. Domning and L. G. Barnes. 1994. A new Middle Miocene sirenian of the genus Metaxytherium from Baja California: relationships and paleobiogeographic implications. Proceedings of the San Diego Society of Natural History 29:191-204.

Domning, D. P., P. D. Gingerich, E. L. Simons and F. A. Ankel-Simons. 1994. A new Early Oligocene dugongid (Mammalia, Sirenia) from Fayum Province, Egypt. Contributions from the Museum of Paleontology, the University of Michigan 29(4):89-108.

Reinhart, R. H. 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36(1):1-146.

A river runs through an Oligocene sea: parte III

2010-03-31T12:28:00.005-04:00

So, keeping up with stuff I’ve collected at the Río G locality (for previous entries about this locality go here and here), I bring you some of the sirenian material that I collected last January. It is not much, but it adds to stuff I’ve collected previously (as you’ll see).

In tropical regions, a lot of times, good outcrops are along riverbanks. Puerto Rico is no exception and that is why the Rio G locality is so good, the exposure is kept “fresh” because of the nearly constant river erosion. Of course the drawback is that fossils are also lost if nobody visits these type of localities at least once a month or after big rainstorms (at least that’s what I used to do).

The picture above shows one such example. I spotted this bone fragment on the wall, very close to water level (a little more than half a meter). And, as you can see in the inset, the surface facing away from the rock looks freshly broken. I did collect the fossil, and unsuccessfully looked for additional fragments nearby.

Above is the picture of the fossil, in dorsal view (anterior towards the top), and the interpretative drawing. As it turns out the fossil was part of a sirenian skull. What was left of the fossil, is the anterior part of the frontals (Fr) and the nasals (N), the supraorbital processes of the frontals are missing. The convex frontal roof and shallow nasal incisure (the concave area between the frontals) are some characters that identify this fossil as belonging to a halitheriine dugongid. In fact, it is very similar to the same part of a much more complete skull that I collected from that locality several years ago (see below).

The figure above shows the more complete skull. A and B show a close-up dorsal view (anterior towards the top) of the area that was preserved in the fragmentary fossil. C is a dorsal view of the skull (anterior to the right) with the outline of the enlarged area in A. As you can see the frontal and its relationship with the nasals look much the same as the fragmentary fossil. It also displays a shallow nasal incisure at the posterior end of the mesorostral fossa (MRF) and convex frontal roof. In the more complete skull the premaxilla (Pmx) partially cover the nasals and the supraorbital processes (SOP) are preserved. (In A and C it is missing the left nasal process of the premaxilla which is loose and needs to be re-attached, but I was able to put it in the drawing).

I’m pretty certain that the fragmentary fossil belongs to the same species as the more complete specimen; it was a pity that part of it was lost previous to it being found. If you’re well acquainted with extinct sirenians, you can probably guess what genus this skull belongs to. So, go ahead and make a guess!

Chevron weirdness in a sirenian

2010-03-04T09:30:00.007-05:00

Following up on a comment I made over at Updates from the Vertebrate Paleontology Lab, I here bring you pictures of an unusual sirenian chevron from the Late Oligocene of Puerto Rico.

These fossils were collected as part of a partial articulated postcranium which I mentioned here. Chevrons, also known as hemal arches, are (normally) V-shaped* bones, consisting of two rami that meet ventrally, hence the shape. They protect blood vessels.

*More like Y-shaped due to the length of the symphysis in some specimens.

In the picture above you can see left lateral views of two of the chevrons I collected with that specimen. The chevron on the left seems to represent fused chevron 2 + 3 (missing part of its ventral edge), and the other one is chevron 4, which is normal.

Here is a posterior view, again, the one on the left likely represents fused chevron 2 + 3, and on the right is chevron 4, which is missing the right ramus.

To me this seems to have been a developmental anomaly rather than occurring due to an injury. Apparently, this is a first, at least for Sirenia! As I mentioned above these are part of an articulated partial postcranium, belonging to a new dugongine taxon from the Late Oligocene of northern Puerto Rico (you can see the skull here).

So, leave a comment, let me know what you think about this unusual bone!

A river runs through an Oligocene sea: parte II

2010-02-14T09:52:00.005-05:00

It’s been a while since the last post, mostly because of a class that takes most of my free time as well as some family situation back in December and January. This is the first post of the year and, hopefully, more will follow. Anyways, today I bring you a little about fieldwork that I did back in January while I was in Puerto Rico. I had written in a previous occasion about this locality (the reason why this is part II) and unlike that other time, I did find some vertebrate fossils.

The picture above is of one of the most productive spots along this locality. As you can see there are about four distinct units. I and III are paleosols (ancient soil horizons) whereas II seems to be shallow marine/brackish and IV shallow marine. Unit II has yielded good fossils in the past, including a sirenian skull and associated axial skeleton (currently under study), croc teeth, a rodent incisor and some nurse shark teeth (gynglymostomatids). These beds are part of the San Sebastian Formation of Early Oligocene age, which in the past have yielded other cool fossils such as the sirenian Caribosiren turneri (Reinhart, 1959) and the gharial Aktiogavialis puertoricencis (Vélez-Juarbe et al. 2007), among others.

Like I mentioned, this time around I did find some cool stuff!

Above is a closeup of unit II showing some of the fossils before I started digging. The red circles are for turtle shell fragments and the green is a sirenian rib. Yes, I know, they are somewhat difficult to see but click on the picture and look carefully, you’ll see them.

The sirenian rib was isolated and easy to collect; it is fairly normal to find isolated sirenian ribs in the San Sebastian Fm and other middle Tertiary localities. While digging around the turtle shell fragments shown in the picture above, I kept stumbling upon more fragments, until it was apparent that this represented a partially disarticulated turtle shell. Not only that, but there was also an associated left pelvis (shown in the picture below), not bad!!

One of my first posts was about the fossil side-neck turtles from Puerto Rico. In it I mentioned that some pelomedusid (a more technical name for side-necks) material from the San Sebastian Fm. had been described by Wood (1972) as an unknown taxon. In fact, Wood (1972) not only described an incomplete shell and plastron but also an associated pelvis. Maybe the material I recently collected represents additional material of that unknown taxon. But comparison with the description as well as with other turtle fossils from the overlying Lares Limestone will have to wait until the summer when I go back to Puerto Rico and open the jackets (you can see them in the picture below).

Oh, by the way, I’m pretty sure this is a pelomedusid, just by the morphology of the pelvis. Hope you enjoyed the pictures! Also, there was one other fossil collected that day (is in the jacket in the far left), it was both interesting and frustrating, but I'll leave that for next time!

Reinhart, R. H. 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36(1):1-146.

Vélez-Juarbe, J., C. A. Brochu & H. Santos. 2007. A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile. Proceedings of the Royal Society B 274:1245-1254.

Wood, R. C. 1972. A fossil pelomedusid turtle from Puerto Rico. Breviora 392:1-13.

Nuevos sirénidos del Eoceno

2009-12-18T10:21:00.013-05:00

Este año ha visto la publicación de dos artículos describiendo sirénidos del Eoceno (55.8-33.9 millones de años atrás [ma]). En adición a esos, otras dos especies más fueron descritos del Mioceno, los cuales mencioné en una entrada pasada. Creo que no está mal, cuatro nuevas especies de sirénidos fósiles en un año, especialmente para un grupo que hoy día solo cuenta con cuatro especies (tres de manatí y el dugong). El conocimiento sobre la diversidad de sirénidos en el pasado sigue aumentando a muy buen ritmo.

Durante el Eoceno existían al menos tres de las cuatro familias de sirénidos que se conocen, Prorastomidae (que incluyen los miembros más primitivos), Protosirenidae y Dugongidae. El registro fósil de los Trichechidae (la cuarta familia, que es la que incluye al manatí) es más escaso y hasta donde sabemos, estos se originaron durante el Oligoceno Tardío (28.4-23 ma). Los nuevos fósiles del Eoceno representan a los Prorastomidae y los Dugongidae.

Un protosirénido de India

En una entrada pasada mencioné que India es uno de los lugares más prolíficos en términos de hallazgos de fósiles de sirénidos. No debe sorprendernos que otra especie adicional ha sido descrita. Ashokia antiqua Bajpai et al. 2009 representa un nuevo género y especie de protosirénido del Eoceno Medio temprano (Lutetian: 48.6-40.4 ma). Esta nueva especie se distingue por una combinación de caracteres primitivos y derivados, morfológicamente se acerca más a otro protosirénido de Libya, aún sin describir (Bajpai et al., 2009). Ashokia se distingue de otros prorastómidos al tener una cresta sigmoidal prominente, la apertura auditiva externa más ancha, el puente zigomatico-orbital elevado, el borde del exoccipital más delgado y poseer un proceso zigomático del hueso temporal que disminuye en grosor gradualmente en dirección al rostro.

En la figura arriba Ashokia antiqua en vista lateral (foto e ilustración hechas por mi).

Este no es el primer prorastómido que se conoce de India. Bajpai et al. (2006) refirieron un cráneo incompleto al género Protosiren sp., este, al igual que Ashokia, provienen de la Formación Harudi. Otros sirénido del Eoceno indio son Eotheroides babiae y Eosiren sp. también de la misma formación, estos sin embargo son dugónguidos (Bajpai et al. 2006). Los protosirénidos se distinguen de todas otras especies conocidas de sirénidos por ciertas características craneales y por tener las epífisis* cartilaginosas, incluso en los adultos (Sickenberg, 1934; Zalmout et al., 2003; Bajpai et al. 2006). Aún no se han reportado protosirénidos en rocas del Oligoceno, por lo que parece que este grupo fue uno exclusivo del Eoceno.

*Los extremos de los huesos.

Un dugónguido de Madagascar

Poco se conoce de los animales que habitaron Madagascar en el pasado. No fue hasta en años recientes que se comenzó a descubrir fósiles de los antiguos pobladores de esta isla, especialmente durante el Mesozoico y Cenozoico. Uno de los descubrimientos más recientes es el cráneo de un dugóngido proveniente de estratas del Eoceno Medio. Estos han sido descritos por Samonds et al. (2009) quienes han identificado el fósil como una especie nueva del género Eotheroides. E. lambondrano Samonds et al. 2009 pertenece a un género de dugónguidos que están se han encontrado en rocas del Eoceno de Egipto e India (Domning, 1996; Bajpai et al., 2006), esta nueva especie es la única dentro de ese género que posee el rostro completo, permitiéndonos conocer su morfología en mayor detalle. Único entre otras especies de Eotheroides por la morfología distinta de los huesos nasales, tener procesos supraorbitales bien desarrollados y el puente zigomatico-orbital de la maxilla corto, también se distingue de otras especies de dugonguidos al poseer una fórmula dental primitiva.

En la figura arriba Eotheroides lambondrano en vista lateral, escala = 4 cm (compuesto de fig. 3A y 4A de Samonds et al., 2009).

El largo del cráneo de E. lambondrano es de 270 mm (~10 pulg.), haciendo de este uno de los dugones de menor dimensión que se conocen. Posiblemente se acercaba en tamaño a las especies de dugónguino Nanosiren los cuales tenian dimensiones similares y cual largo total de cuerpo se estima en alrededor de 2 metros (~6’6”) (Domning & Aguilera, 2008), lo cual es considerado pequeño para un sirénido adulto. Asi que según se ha escrito en otros lugares (como en este artículo de National Geographic) puede que la nueva especie de Madagascar sea el dugónguido más pequeño que conocemos.

La importancia de estos nuevos fósiles resta en que demuestran cuan diverso eran los sirénidos durante el Eoceno. El nuevo protosirénido añade otra especie a un interesante grupo de sirénidos, que incluso se ha postulado como el grupo que dio origen a los Trichechidae. El hallazgo de Eotheroides lambondrano en Madagascar nos muestra cuán amplia era la distribución de este género y de los dugónguidos durante el Eoceno; en adición nos puede ayudar a entender la evolución de estos en la región del Tethys. Y por supuesto, aquellos de nosotros que están al tanto de lo que ocurren en el mundo de la paleosirenología saben que aún quedan más por ser descritos, asi que pendientes!

Otras entradas sobre sirénidos

Prep work: update II and a note on sirenian periotics

Prep work: update

Sirenian diversity in the past

De la tierra al agua (English version here)

Domningia and other Indian sirenians

What’s wrong with the hands of Steller’s sea cow

Bajpai, S., D. P. Domning, D. P. Das & V. P. Mishra. 2009. A new middle Eocene sirenian (Mammalia, Protosirenidae) from India. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen 252/3:257-267.

Bajpai, S., J. G. M. Thewissen, V. V. Kapur, B. N. Tewari & A. Sahni. 2006. Eocene and Oligocene sirenians (Mammalia) from Kachchh, India. Journal of Vertebrate Paleontology 26(2):400-410.

Domning, D. P. 1996. Bibliography and index of the Sirenia and Desmostylia. Smithsonian Contributions to Paleobiology 80:1-611.

Domning, D. P. & O. A. Aguilera. 2008. Fossil Sirenia of the West Atlantic and Caribbean region. VIII. Nanosiren garciae, gen. et sp. nov. and Nanosiren sanchezi, sp. nov. Journal of Vertebrate Paleontology 28(2):479-500.

Samonds, K. E., I. S. Zalmout, M. Irwin, D. W. Krause, R. R. Rogers & L. L. Raharivony. 2009. Eotheroides lambondrano, new Middle Eocene seacow (Mammalia, Sirenia) from the Mahajanga basin, northwestern Madagascar. Journal of Vertebrate Paleontology 29(4):1233-1243.

Prep work: update II and a note on sirenian periotics

2009-11-19T11:07:00.008-05:00

This has been a long hiatus! I’ve been really busy doing some more prep work on the Puerto Rican Dioplotherium and the Yucatán skull (another new species of dugongine). On top of that I’ve been preparing a couple of manuscripts describing some sirenian remains from PR, which I hope to submit sometime next year.

The subject of this post is to show you more of the Puerto Rican Dioplotherium, which was featured on the previous post. I have done additional prep work on the left squamosal, which was detached from the skull.

The composite picture above shows the skull as it was back in 2006 (top picture) and an outline of the enlarged area below. All that was visible of the sqamosal were the zygomatic arch, post-tympanic process and the mastoid part of the periotic (bottom picture). It was exciting knowing that part of the ear bones were preserved, even if it was only the periotic. Fortunately I got more than I bargained for.

In this figure we see the squamosal, now free of matrix, in lateral (A) and medial (B) views. Notice that the tympanic bone was preserved as well as the periotic. And there is more!

Additional removal of matrix revealed the three auditory ossicles, in articulation! The picture below shows a posteroventral view into the middle ear (anterior is to the right, medial towards the top of the picture). This is really neat as these bones are easily lost in most fossils (they are, apparently, missing on the right side of the skull).

A little on sirenian periotics

The periotic can be divided into three parts tegmen tympani, pars mastoidea and pars petrosa. The latter can be subdivided into pars canalicularis and pars cochlearis (see picture above) (Robineau, 1969). In the pars cochlearis, the structure labeled perilymphatic foramen, is uniquely found in (most) sirenians, (most) proboscideans and Arsinoitherium (hinting at their tethytherian affinity?). The homologous structure in other mammals consists of two openings known as the fenestra cochleae (rotunda) and aqueductus cochleae (Court, 1994).

The occurrence of a perilymphatic foramen in some tethytheres (I’m not sure what is the condition in desmostylians) seems to indicate that it might be a unique derived character of the group. Nonetheless, when we look at the fossil record, primitive proboscideans (Phosphatherium escuilliei) and sirenians (Prorastomus sirenoides) do have fenestra cochleae and aqueductus cochleae (Gheerbrant et al., 2005; Court, 1990; Savage et al., 1994). Meaning that this condition is homoplasic in tethytheres (Court, 1994, Gheerbrant et al. 2005). Whether resulting from multiple origins or multiple reversals, I still think it is an interesting characteristic that is found in at least some tethytheres.

Previous post about sirenians:

Prep work: update

Sirenian diversity in the past

De la tierra al agua (English version here)

Domningia and other Indian sirenians

What's wrong with the hands of Steller's sea cow

Court, N. 1990. Perotic anatomy of Arsinoitherium (Mammalia, Embrithopoda) and its phylogenetic implications. Journal of Vertebrate Paleontology 10(2):170-182.

Court, N. 1994. The periotic of Moeritherium (Mammalia, Proboscidea): homology or homoplasy in the ear region of Tethytheria McKenna, 1975? Zoological Journal of the Linnean Society 112:13-28.

Gheerbrant, E., J. Sudre, P. Tassy, M. Amaghzaz, B. Bouya and M. Iarochène. 2005. Nouvelles données sur Phosphatherium escuilliei (Mammalia, Proboscidea) de ‘Éocène inférieur du Maroc, apports à la phylogénie des Proboscidea et des ongulés lophodontes. Geodiversitas 27(2):239-333.

Robineau, D. 1969. Morphologie externe du complexe osseux temporal chez les sireniens. Mémoires du Muséum National d’Histoire Naturelle, Série A, Zoologie 60(1)-1-32.

Savage, R. J. G., D. P. Domning and J. G. M. Thewissen. 1994. Fossil Sirenia of the west Atlantic and Caribbean region. V. The most primitive known sirenian, Prorastomus sirenoides Owen, 1855. Journal of Vertebrate Paleontology 14(3):427-449.

Prep Work: Update

2009-09-18T11:25:00.006-04:00

Wow! It’s been a while since I posted something. Working with some of the material collected back in August when I went to Puerto Rico to do fieldwork with my advisor has kept me busy. In addition, I had no computer for a while, just after posting the previous post, my computer’s hard drive died! Luckily, not much was lost.

Back in June I wrote about some prep work I had been doing on a sirenian skull from Puerto Rico. Well I am glad to say that four years after I collected said skull (in 2005), it is nearly done! So, here are some pictures, from the time it was collected until now.

In the picture above (from 2005) I am in the outcrop with my hand next to where the fossil is. This is a Late Oligocene limestone unit from northern Puerto Rico.

Here is a dorsal and right lateral view of how the fossil looked around 2006 (and actually it looked like that for the last 2 years). You might notice that on the top picture there is a bone floating in the matrix next to the braincase, this is the left squamosal, which is disarticulated.

Here is how the fossil looks like now (2009), with most of the matrix gone and the left squamosal removed. Beautiful, don't you think?!

If you know something about sirenians, you might have noticed that this is a dugongine (large tusks [broken, unfortunately], thickened supraorbital process of frontal, etc.). It is actually quite similar to Dioplotherium manigaulti from the Early Miocene of South Carolina and Florida (Cope, 1883; Domning, 1989). Nonetheless, the Puerto Rican skull is older, Late Oligocene, and it also has some primitive characters that sets it apart from D. manigaulti. This skull along with another one from the same locality make up an important part of my thesis. Fortunately, some postcranial material that was collected this summer, from the same outcrop and same unit, is referable to this taxon. This material also displays differences from other known sirenian postcrania. Pretty cool stuff!!

Previous post about sirenians:

Sirenian diversity in the past

De la tierra al agua (English version here)

Domningia and other Indian sirenians

What's wrong with the hands of Steller's sea cow

Cope, E. D. 1883. On a new extinct genus of Sirenia from South Carolina. Proceedings, Academy of Natural Sciences of Philadelphia 1883:52-54.

Domning, D. P. 1989. Fossil Sirenia of the West Atlantic and Caribbean region. II. Dioplotherium manigualti Cope, 1883. Journal of Vertebrate Paleontology 9:415-428.

Sirenian diversity in the past

2009-07-27T16:15:00.007-04:00

Its been quiet here for a while as I’ve been busy working on the preparation of two sirenians skull, as well as getting ready for the upcoming field season.

It’s also been a while since I wrote something about sirenians so, here it goes.

Living sirenians can be divided into two families, Trichechidae (manatees) and Dugongidae (dugongs). Most people are probably more familiar with the manatees, after all, there are three species, West Indian, Amazonian and African, whereas there is only one species of dugong. The geographic distribution of extant sirenians is such that there is mostly no overlap between the different species. As the only living herbivorous marine mammals, it might be that by living in separate regions it reduced the chances of competing for the same resources (i.e. seagrasses). But what about in the past, what does the fossil record of sirenian tells us about their paleoecology.

When we look at the fossil record, sirenians were much more speciose, including multispecies communities in some regions (Domning, 2001). Now lets look at one good example.

The Late Oligocene of Florida

The Late Oligocene sirenian fauna of Florida includes at least three species of dugongids*. The dugongines, Crenatosiren olseni and Dioplotherium manigaulti, and the halitheriine Metaxytherium sp. (Domning, 1989, 1997, 2001). (See illustration below).

*The family Dugongidae includes three subfamilies: Dugonginae, Halitheriinae & Hydrodamalinae.

Illustration of known Late Oligocene sirenians from Florida (all at the same scale). Top, Crenatosiren olseni (modified from Domning, 1997); middle, Dioplotherium manigaulti (from Domning, 1989); bottom, Metaxytherium sp. (this last drawing based on a very similar skull from Puerto Rico, tusks not preserved, but presumed to be small as in the Fl specimen). The numbers in the circles are the degrees of rostral deflection. Mandibles absent in the middle and bottom specimens.

These three species, as you can see, differ in size, and to a lesser degree in rostral deflection. Also different from each other is the size of their tusks, increasing in size from Metaxytherium - C. olseni - Dioplotherium manigaulti. Taken as a whole, these differences (specially tusks size) could be indicators of different feeding habits, with small-tusked sirenians feeding of small rhizomes* and large-tusked sirenians feeding on larger ones (Domning, 2001; Domning & Beatty, 2007). Dugongids most likely used their tusks as a tool to dig out the rhizomes, with the most extreme specialization observed in the dugongines, including very large blade-like tusks as well as cranial adaptations that seemed to have help withstand the forces exerted when digging (Domning & Beatty, 2007).

*Rhizomes = the nutrient-rich, underground stems of seagrasses.

Other examples of sirenian multispecies communities are found in the Early Oligocene of Puerto Rico and the Early Miocene of India, among others (more on this sometime in the future). In addition, in the Pacific, sirenians were not the only herbivorous marine mammals. In the northern Pacific region, sirenians seem to have shared their resources with the desmostylians (see picture below), an interesting (and bizarre) group of mammals that lived from the Oligocene to the Miocene and were presumably feeding and spending time in the marine realm (Domning et al., 1986; Inuzuka et al., 1994). Whereas, in the southeastern Pacific, fossils of aquatic sloths (Thalassocnus spp.) have been found in the same formations as sirenians (Muizon & McDonald, 1995; Canto et al., 2008; Muizon & Domning, 1985; Bianucci et al., 2006; Domning & Aguilera, 2008).

Mounted cast of Palaeoparadoxia tabatai taken at the AMNH.

So, why is it so different in modern times, why do we see such a reduced diversity of sirenians and/or lack of any other herbivorous marine mammals? There has been, apparently, little change in the marine seagrass communities since the Eocene, so what happened? The answers for these and other questions could be answered with more fossils and more research. For now, we can certainly say that, like their close relatives, the proboscideans (elephants), sirenians are the last remnants of a once much more diverse group of animals.

References

Bianucci, G., S. Sorbi, M. E. Suárez & W. Landini. 2006. The southernmost sirenian record in the eastern Pacific Ocean, from the Late Miocene of Chile. Comptes Rendus Palevol 5:945-952.

Canto, J., R. Salas-Gismondi, M. Cozzuol & J. Yáñez. 2008. The aquatic sloth Thalassocnus (Mammalia, Xenarthra) from the Late Miocene of north-central Chile: biogeographic and ecological implications. Journal of Vertebrate Paleontology 28(3):918-922.

Domning, D. P. 1989. Fossil Sirenia of the West Atlantic and Caribbean region. II. Dioplotherium manigaulti Cope, 1883. Journal of Vertebrate Paleontology 9:415-428.

Domning, D. P. 1997. Fossil Sirenia of the West Atlantic and Caribbean region. VI. Crenatosiren olseni (Reinhart, 1976). Journal of Vertebrate Paleontology 17:397-412.

Domning, D. P. 2001. Sirenians, seagrasses, and Cenozoic ecological change in the Caribbean. Palaeogeography, Palaeoclimatology, Palaeoecology 166:27-50.

Domning, D. P. & B. L. Beatty. 2007. Use of tusks in feeding by dugongid sirenians: observations and tests of hypotheses. Anatomical Record 290:523-538.

Domning, D. P., C. E. Ray & M. C. Mckenna. 1986. Two new Oligocene desmostylians and a discussion of Tethytherian systematics. Smithsonian Contributions to Paleobiology 59:1-56.

Inuzuka, N., D. P. Domning & C. E. Ray. 1994. Summary of taxa and morphological adaptations of the Desmostylia. Island Arc 3(4):522-537.

Muizon, C. de & D. P. Domning. 1985. The first records of fossil sirenians in the southeastern Pacific Ocean. Bulletin du Muséum National d’Histoire Naturelle (Paris) (4)7, Sect. C, no. 3:189-213.

Muizon, C. de & H. G. McDonald. 1995. An aquatic sloth from the Pliocene of Perú. Nature 375:224-227.

A day in the field, Tertiary

2009-06-30T23:09:00.004-04:00

This time our field area is in northern Puerto Rico. We decided to visits a couple of outcrops of the Late Oligocene Lares Limestone. If the name of the formation sounds familiar you either know about the geology of Puerto Rico or, have read about it on a previous post.

One of these localities (see picture below), I have visited at least since 2000, and up until very recently, we thought that the only formations present there were the Early Oligocene San Sebastián Formation and the overlying Lares Limestone. Now, thanks to new information regarding the stratigraphy of the Tertiary limestones of the north coast of Puerto Rico (Ortega Ariza, 2009), we know that in this locality, overlying the Lares Ls, there are also units of the Montebello Limestone. The age of the Lares Limestone and Montebello Limestone were designated as Late Oligocene – lower Early Miocene and upper Early Miocene, respectively (Seiglie & Moussa, 1984). New data, using strontium isotopes obtained from tubes of the pelecypod Kuphus incrassatus, seems to indicate, instead, that both formations span the Late Oligocene (Johnson et al., 2006; Ramírez et al., 2006; Ortega Ariza, 2009). If this is correct (more samples need to be run, hint, hint!!) I will like this outcrop even more (sorry, can't hide my love for the Oligocene)!!

Here's the one of my favorite outcrops, where the Lares and Montebello limestones are exposed. The arrow points to a sirenian fossil that is yet to be collected.

Of course, what I’ve been mostly searching in these localities are sirenian remains, but like I mentioned on that previous post, other vertebrates have also been collected. Interestingly, the best sirenian remains have been collected from the upper Lares Limestone, with a total (so far) of two skulls, and a set of nine articulated vertebrae (see picture below). There are more fossils but those will be collected in due time. As for the sirenian skulls, well, they are an important part of my thesis work and I will discuss them at some point in the future.

Some articulated sirenian vertebrae, these have already been collected. This is an earlier picture, there were three more vertebrae behind the one labeled Ca1, the ones anterior to L3 were collected earlier.

References

Johnson, C. C., W. R. Ramírez, L. R. Mark, S. Y. Hernandez, E. A. Barrow, M. Hegewald & J. Velez. 2006. Oligocene reef deposits linked to OPD site 999 with strontium isotope stratigraphy. Geological Society of America Abstracts with Program 38:557.

Ortega Ariza, D. L. 2009. Establishing a high resolution sequence stratigraphy and sea-level curve for Tertiary limestones, Puerto Rico. M.S. thesis, University of Puerto Rico, Mayagüez, Puerto Rico, 132 pp.

Ramírez, W. R., C. C. Johnson, M. Martínez, M. C. Torres & V. Ortiz. 2006. Strontium isotope stratigraphy from Kuphus incrassatus, Cenozoic limestones, Puerto Rico. Geological Society of America Abstracts with Program 38:90.

Seiglie, G. A. & M. T. Moussa. 1984. Late Oligocene-Pliocene trangressive-regressive cycles of sedimentation in northwestern Puerto Rico. American Association of Petroleum Geologist Memoir 36:89-95.

A day in the field: Cretaceous

2009-06-17T02:35:00.005-04:00

Cretaceous sedimentary rocks are found in Puerto Rico, especially in the southwest part of the island where several well-exposed limestone units are exposed. Our destination this time was a new outcrop of the Parguera Limestone. Located in the Southwest Igneous Province (Jolly et al., 1998; Schellekens, 1998), this formation, which ranges from Santonian to Campanian, has been divided into three units, the lower Bahia Fosforecente Member, the middle Punta Papayo Member and the upper Isla Magueyes Member (Almy, 1965). Like a lot of the Cretaceous limestone units in the Caribbean region, the age has been determined with the aid of the rudist bivalve assemblages, which have been divided into several biozones (Rojas et al., 1995).

A couple of rudist bivalves (red outline). During life the position of these was with the narrowest part semi-buried in the substratum (elevators). As we can see these are sideways.

There was some debate as to whether the outcrop we went to was part of the Bahia Fosforecente or Punta Papayo, the former which has been dated as Santonian whereas the latter as Campanian in age. Lithologically, this locality is most similar to the Bahia Fosforecente member. As we searched for fossils, we found several rudists (see picture above). These seem to have been transported, as these are elevators, but were found on their side. Although these were mostly complete, I must say I haven’t had the time to look in detail at their morphology, hence they remain nameless, for now.

One of the unknown rudist we collected (left); fragment of Macgillavryia nicholasi, notice the cell pattern (right).

Other rudists that were more fragmentary, were actually much more helpful for pinning down the age of the rocks here. Several fragments of the large* rudist Macgillavryia nicholasi were found and we were able to make an ID based on their diagnostic cell patterns (picture above) (Rojas et al., 1995). The occurrence of M. nicholasi indicates that these deposits are Campanian in age, as they are found in the Barrettia monilifera biozone of Rojas et al. (1995), meaning that these units are probably part of the Punta Papayo member.

*Some specimens reaching a diameter up to 1 meter!

In terms of the depositional environment, the Parguera limestone represents (mostly) slope to basin environments (Almy, 1965). This outcrop is different. The lithology here indicates that this was likely a nearshore deposit in a moderate/high-energy coast; sandy flat pebble conglomerates were the giveaway.

View of the outcrop of Parguera Limestone, rocks are dipping to the south (towards the left). To the far right, HSM & DLOA search for fossils.

Leaving what I think is most exiting for last; the whole reason for our visit to this outcrop was the search for fossils of tetrapods. One of us (DLOA) had found, on a previous visit, a non-fish vertebra*! We did not found anything else, but if we can get an id on what we have so far it would be a first! So, wish us luck!

*Update (Aug/2009): it most likely is an archosaur caudal vertebra!! Hat tip to MTC for the id!

Go here for a very good rudist database.

References

Almy, C. C., Jr. 1965. Parguera Limestone, Upper Cretaceous, Mayagüez Group, Southwestern Puerto Rico. Unpublished Ph.D. thesis, Rice University, Houston, 203p.

Jolly, W. T., E. G. Lidiak, J. H. Schellekens & H. Santos. 1998. Volcanism, tectonics, and stratigraphic correlations in Puerto Rico; pp. 1-34 in E. G. Lidiak & D. A. Larue (eds.), Tectonics and Geochemistry of the Northeastern Caribbean. Geological Society of America Special Paper 322.

Rojas, R., M. A. Iturralde-Vinent and P. W. Skelton. 1995. Stratigraphy, composition and age of Cuban rudist-bearing deposits. Revista Mexicana de Ciencias Geológicas 12(2):272-291.

Schellekens, J. H. 1998. Geochemical evolution and tectonic history of Puerto Rico; pp. 35-66, in E. G. Lidiak & D. A. Larue (eds.), Tectonics and Geochemistry of the Northeastern Caribbean. Geological Society of America Special Paper 322.

From land to sea

2009-06-09T22:14:00.005-04:00

Some of the living marine mammals, like cetaceans, sirenians and pinnipeds* are so well adapted to a life in water that it might be difficult for us to relate them to their closest terrestrial relatives. However, we do know that the oldest members of these groups were indeed terrestrial. Here I’ll discuss some of the evidence known so far.

*(cetaceans = whales & dolphins; sirenians = manatees & dugongs; pinnipeds = seals, walruses & sea lion).

Cetaceans

Modern whales can be divided into two groups, odontocetes and mysticetes. Odontocetes are characterized for having teeth and using echolocation; mysticetes are characterized for having baleen instead of teeth (there are other adaptations that I won’t discuss now). Some examples of odontocetes are orcas and bottlenose dolphins; mysticetes include blue whales and right whales.

Based on molecular evidence, whales evolved from artiodactyls – a group that includes pigs, hippopotamus, camels, cows, lambs, etc – (Graur & Higgins, 1994; Shimamura et al., 1997), whereas, for a long time, morphological studies used to indicate a close relationship with mesonychids – a group of extinct terrestrial carnivores – (Luo & Gingerich, 1999). In part, the reason for this disagreement about the origin of whales was that the oldest fossils of cetaceans consisted of forms that were already completely adapted to a life in the water, or were only known from crania. This has already been resolved.

In 2001, two groups of paleontologist published papers where they described primitive cetaceans, including parts of the postcranium that corroborated an artiodactyl relationship (Gingerich et al., 2001; Thewissen et al., 2001). Gingerich and his team found remains of Artiocetus clavis and Rhodocetus balochistanensis, whereas the Thewissen team described Ichthyolestes pinfoldi and Pakicetus attocki (illustration above of Pakicetus by Carl Buell, taken from the Thewissen Lab webpage); the remains included one of the ankle bones, the astragalus, which was key to determine that cetaceans evolved from artiodactyls. All these fossils were found Middle Eocene (49-41 million years ago) deposits. More recently, Thewissen et al. (2007) describe postcranial material of the primitive artiodactyl, Indohyus, and show that it was an animal with aquatic adaptations, providing additional evidence about the origin of cetaceans. (Go here for a magnificent reconstruction of Indohyus).

Sirenians

The closest living relatives of manatees and dugongs are elephants, this relationships is supported by both, molecular and morphological evidence (Seiffert, 2007; Tabuce et al. 2007). Sirenians originated in northern Africa about 54 million years ago, where they last shared a common ancestor with proboscideans (elephants). Interestingly, the most primitive sirenian fossils have been found in Jamaica, which demonstrate that, very early, they seem to have been well adapted for life in an aquatic environment. For a long time, the most primitive sirenian known was Prorastomus sirenoides found in Jamaica in deposits that are between 51-49 million years old (Owen, 1855; Savage et al., 1994). Unfortunately, the postcranium was and it is still mostly unknown.

Another sirenian from Jamaica, found in slightly younger deposits – 49-45 million years old – was described by Domning (2001). The remains of this new sirenian, named Pezosiren portelli (illustration above from Domning, 2001), include cranial and postcranial material. The postcranial material include fore and hind limbs, pelvis and most of the vertebral column; all together, these indicate that Pezosiren was able to support its own weight on land, but at the same time, it had aquatic adaptations such as pachyosteosclerotic (enlarged & dense) ribs and in the cranium, retracted external nares (Domning, 2001). The combination of characters imply that Pezosiren spent time, both, in and out of the water.

Pinnipeds

Morphological and molecular studies show that pinnipeds belong to a group of mammals called arctoids (Deméré et al., 2003), that, along with pinnipeds, includes bears (ursids), weasels (mustelids), raccoons (procyonids) and skunks (mephitids), among others. Nonetheless, the origin of pinnipeds from one of these arctoids is not clear, and different studies place pinnipeds as originating from a common ancestor with mustelids or with ursids (Deméré et al., 2003). Other experts in the field support a multiple origin for pinnipeds, with seals sharing a common ancestor with mustelids and sea lion and walruses with ursids (Uhen, 2007 and references therein). Anyways, whatever is the group from which pinnipeds originated – this can only be resolved by finding more fossils – it is well known that these originate from a terrestrial ancestor. Interestingly, pinniped fossils that show a transitional morphology had not been found until recently.

The discovery of Puijila darwini in lacustrine sediments deposited between 23-21 million years ago, gives us an idea about the morphology of the earliest pinnipeds (Rybczynski et al., 2009). Although fossils of yet even older pinnipeds, such as Enaliarctos tedfordi and E. barnesi, have been found in rocks that date between 28.5-23.8 million years in Oregon (Deméré et al., 2003), these already show full adaptations to a life in the marine realm like those observed in modern taxa; this means that pinnipeds must have evolved previous to that date. So, even if Puijila (illustration above from Rybczynski et al., 2009) comes from younger deposits, its importance rests in that morphologically it is the most primitive known pinnipeds, providing evidence about the evolutionary steps that were taken in the transition from land to sea in this group of mammals.

Puijila the official website

Puijila in National Geographic

Also, here is the Spanish version of this post.

References

Deméré, T. A., A. Berta & P. J. Adams. 2003. Pinnipedomorph evolutionary biogeography. Bulletin of the American Museum of Natural History 279:32-76.

Domning, D. P. 2001. The earliest known fully quadrupedal sirenian. Nature 413:625-627.

Gingerich, P. D., M. ul Haq, I. S. Zalmout, I. H. Khan & M. S. Malkani. 2001. Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan. Science 293:2239-2242.

Graur, D. & D. G. Higgins. 1994. Molecular evidence for the inclusion of cetaceans within the order Artiodactyla. Molecular Biology and Evolution 11(3):357-364.

Luo, Z. & P. D. Gingerich. 1999. Terrestrial Mesonychia to aquatic Cetacea: transformation of the basicranium and evolution of hearing in whales. University of Michigan Papers on Paleontology 31:1-98.

Owen, R. 1855. On the fossil skull of a mammal (Prorastomus sirenoides, Owen), from the island of Jamaica. Quarterly Journal of the Geological Society of London 11:541-543.

Rybczynski, N., M. R. Dawson & R. H. Tedford. 2009. A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia. Nature 458:1021-1024.

Savage, R. J. G., D. P. Domning & J. G. M. Thewissen. 1994. Fossil Sirenia of the West Atlantic and Caribbean region. V. Prorastomus sirenoides Owen, 1855. Journal of Vertebrate Paleontology 14(3):427-449.

Seiffert, E. R. 2007. A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic, morphological, and fossil evidence. BMC Ecolutionary Biology 7:224 Open access

Shimamura, M., H. Yasue, K. Ohshima, H. Abe, H. Kato, T. Kishiro, M. Goto, I. Munechika & N. Okada. 1997. Molecular evidence from retroposons that whales form a clade within even-toed ungulates. Nature 388:666-670.

Tabuce, R., L. Marivaux, M. Adaci, M. Bensalah, J.-L. Hartenberger, M. Mahboubi, F. Mebrouk, P. Tafforeau & J.-J. Jaeger. 2007. Early Tertiary mammals from North Africa reinforce the molecular Afrotheria clade. Proceedings of the Royal Society B 274:1159-1166.

Thewissen, J. G. M., E. M. Williams, L. J. Roe & S. T. Hussain. 2001. Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature 413:277-281.

Thewissen, J. G. M., L. N. Cooper, M. T. Clementz, S. Bajpai & B. N. Tiwari. 2007. Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature 450:1190-1195.

Uhen, M. D. 2007. Evolution of marine mammals: back to the sea after 300 million years. Anatomical Record 290:514-522.

Field err… lab work

2009-06-04T01:32:00.008-04:00

It’s field season of course, so I’ve been in Puerto Rico for a while now, unfortunately with my car dead, it has been difficult to do things. I actually wanted to leave fieldwork for latter in the summer and do some lab work now, and I have, to some extent. The lab work includes preparation of some crocodylian postcranial material and a sirenian skull. Of course, I haven’t really been able to keep myself from doing some fieldwork. So here’s some of what has been going on lately.

Lab work

The crocodylian material consists of vertebrae, ribs and dorsal osteoderms from the Early Oligocene San Sebastián Formation in northern Puerto Rico (see picture below). Fossil crocodylians have previously been collected from this formation (go here for a previous post on Caribbean crocs). The material I am currently preparing has been slowly collected (thanks to a dangerous overhang) since 2006 from a unit that sits several meters below the unit where the cranium of Aktiogavialis puertoricensis was found (they were found the same day). With no known cranial material associated to this fossils, it cannot be referred to Aktiogavialis.

A couple of crocodylian ribs (center and lower left) from the San Sebastián Fm. This matrix is no fun.

The sirenian skull, originally found in 2003 and latter collected in 2005, belongs to an adult individual and it comes from the Late Oligocene Lares Limestone. Another skull, from a subadult individual that was collected in 2003 just meters away, both belong to the same dugongine taxon; these are part of my thesis project and will be properly described at some point. They represent the first sirenian cranial remains from this formation; sirenian fossils are known from the underlying San Sebastián Fm and overlying Cibao Fm (Reinhart, 1959; MacPhee & Wyss, 1990).

Trying to remove some annoying matrix from the Lares sirenian.

Field work

So far I’ve been to the field once. Colleagues from the Geology Department at UPRM and myself went to northwestern Puerto Rico, first to visit some people who had some fossils they wanted identified and then to do some actual fieldwork. The first part of the day was somewhat disappointing, as some of the fossils we saw were quite nice and useful, but, sigh, like on previous occasions, the owners of the fossils are unwilling to donate or loan these for research purpose. I always wonder what these people intend to do with the fossils?! Ignorance about geology and paleontology (probably science in general) as well as the lack of a natural history museum in the island is to blame (in part).

Anyways, after a very nice lunch and a lot of rain, we were able to finally visit a new outcrop of the San Sebastián Fm, which is very close to one of my favorite localities, Rio G. Although there is a very interesting exposure of the San Sebastián Fm, it was very unproductive in terms of vertebrates. Some jumbled fish bones, a shark tooth and a bunch of turtle shell fragments was all we found.

Left: tiger shark tooth, Galeocerdo sp.; Right: turtle shell fragments.

Invertebrates were more numerous and nicely preserved, especially crabs. The fossil crustaceans fauna of Puerto Rico was largely unknown until recently (see Schweitzer et al. 2006, 2008). Schweitzer and colleagues looked at fossil crustacean from Cretaceous, Oligocene, Miocene and Pleistocene and report about 13 species, seven which are new. In our new locality we found about three taxa (see picture below).

Lower left: Scylla costata reported in Puerto Rico from the San Sebastián Fm and also from the Juana Díaz Fm; Upper left: cf. Necronectes collinsi also known from the Juana Díaz Fm and Lares Ls; Right: Portunus sp.

Well, that’s it so far. More fieldwork coming soon!

References

MacPhee, R. D. E. & A. R. Wyss. 1990. Oligo-Miocene vertebrates from Puerto Rico, with a catalog of localities. American Museum Novitates 2965:1-45.

Reinhart, R. H. 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36:1-146.

Schweitzer, C. E., M. Iturralde-Vinent, J. L. Hetler & J. Velez-Juarbe. 2006. Oligocene and Miocene decapods (Thalassinidea and Brachyura) from the Caribbean. Annals of the Carnegie Museum 75(2):111-136.

Schweitzer, C. E., J. Velez-Juarbe, M. Martinez, A. Collmar Hull, R. M. Feldmann & H. Santos. 2008. New Cretaceous and Cenozoic Decapoda (Crustacea: Thalassinidea, Brachyura) from Puerto Rico, United States Territory. Bulletin of the Mizunami Fossil Museum 34:1-15.

Cenozoic Caribbean Crocodylians

2009-05-19T14:29:00.018-04:00

Following up* on some neat articles about endemic island crocs over at Tetrapod Zoology (go here and here). I now bring you what is known so far about the Cenozoic crocodylians of the Caribbean Region.

*or at least trying to!

Eocene

The only Eocene crocodylian known so far from the Caribbean region is Charactosuchus kugleri from the Eocene of Jamaica (Berg, 1969). Described from a mandible missing posterior part, it represents the earliest record of a Tertiary crocodylian from the Greater Antilles. Other species of Charactosuchus come from geologically younger deposits in South America (Langston, 1965; Langston & Gasparini, 1997). Doubts about the generic affinities of Charactosuchus kugleri were raised by Domning & Clark (1993) who mention that it is more similar to the tomistomine Dollosuchus dixoni from the Eocene of Europe. Brochu (2007b) upon examination of material referred to D. dixoni, agreed with Domning & Clark (1993) in that C. kugleri might belong to Dollosuchus. In that same work Brochu also considered the name Dollosuchus as nomen dubium, as it is based on material that is too incomplete to offer real information on its affinities. A skull and associated skeleton from the Middle Eocene of Belgium that had been referred to D. dixoni has been redescribed and renamed as Dollosuchoides densmorei by Brochu (2007b).

Oligocene

The next time period from which crocodylian fossils are known from the Caribbean is the Oligocene of Puerto Rico. Early Oligocene remains have been collected from the San Sebastián and Juana Díaz formations, from northern and southern Puerto Rico, respectively. Further collecting efforts have yielded material from the Late Oligocene Lares Limestone and Early Miocene Cibao Formation, both found in northern Puerto Rico. Some of the material from the San Sebastián, Lares and Cibao formations was described by Brochu et al. (2007). The fossils from the San Sebastián Fm are from collections made in the early 1900’s by Narciso Rabell-Cabrero (probably the first Puerto Rican paleontologist) and by the AMNH in the late 1980’s (MacPhee & Wyss, 1990; Brochu et al., 2007). Although these are very fragmentary, and come from different localities, they are very interesting in that they show resemblance to gavialoids (Brochu et al., 2007), and were kind of a preview of what was soon to be found.

Dorsal view of skull of Aktiogavialis puertoricensis, while still under preparation; anterior end points downward. Large openings are supratemporal fenestrae.

It wasn’t until latter in 2006 when paleontologists from the Geology Department at the University of Puerto Rico, collected a partial cranium (see picture above) from deltaic deposits of the San Sebastián Fm. The fossil was described as a new gavialoid taxon, Aktiogavialis puertoricensis, that showed affinities to the South American gharials such as Gryposuchus colombianus, Ikanogavialis gameroi, Piscogavialis jugaliperforatus and Siquisiquesuchus venezuelensis (Vélez-Juarbe et al., 2007). An interesting aspects of the Puerto Rican gharial is its age, known from Early Oligocene deposits, it is the oldest gryposuchine*, a group whose other members are found in Miocene or Pliocene deposits (Langston, 1965; Gasparini, 1968; Sill, 1970; Langston & Gasparini, 1997; Kraus, 1998; Brochu & Rincón, 2004; Riff & Aguilera, 2008). Phylogenetic analysis show that gryposuchines are closely related to extant Gavialis gangeticus (shown below) and North African gavialoids (Brochu & Rincón, 2004; Vélez-Juarbe et al., 2007). This implies that they originated from a North African form that dispersed to the new world prior to the Early Oligocene (Vélez-Juarbe et al., 2007).

*Gryposuchinae: a monophyletic group that includes all the South American gharials (Vélez-Juarbe et al., 2007). The monophyly of this group has been supported by Brochu & Rincón (2004) and Riff & Aguilera (2008) as well; it has been challenged by Jouve et al. (2006; 2008).

Gavialis gangeticus photographed at the National Zoo, Washington, DC.

Not much has been collected from the Late Oligocene Lares Limestone in northern Puerto Rico. A vertebra was described in Brochu et al. (2007), but it is not informative enough; some isolated teeth resembling those of long-snouted croc have also been found. Other teeth, though, are much larger and seem to be from a short-snouted form (see picture below).

Crocodylian teeth from the Lares Limestone, northern Puerto Rico. Scale bar = 1 cm.

Miocene

The Miocene crocodylians of the Caribbean region are still a mystery. Early Miocene crocodylian remains have been collected in Cuba, Dominican Republic and Puerto Rico (MacPhee & Wyss, 1990; MacPhee et al., 2003; Brochu et al., 2007). The Cuban and Dominican material is still undescribed, hence their affinities are unknown. The fossils from Puerto Rico, consisting of several associated cranial elements (shown below) were collected from the Early Miocene age Cibao Fm (MacPhee & Wyss, 1990; Brochu et al., 2007). The Cibao fossils consisting of a partial dentary, frontal and partial left squamosal, show a combination of features that excludes it from being a gavialoid, alligatorid, Crocodylus or any other extant taxon (Brochu et al., 2007). This implies that at least during the Early Miocene (and probably even earlier) Puerto Rico, and possibly other islands in the Caribbean as well, where home to an endemic group of crocodylians.

Crocodylian remains from the Early Miocene Cibao Formation of northern Puerto Rico. From Brochu et al., 2007.

Other radiations of island-endemic crocodylians include the extinct Cenozoic Australasian Mekosuchinae and the extant Osteolaeminae, which includes two extinct island endemics: Voay robustus, from Madagascar (Brochu, 2007a; Bickelmann & Klein, 2009) and possibly Aldabrachampsus dilophus, from Aldabra (Brochu, 2006), both from Quaternary deposits.

Quaternary

Finally, during the Quaternary the Cuban crocodile, Crocodylus rhombifer (shown below) had a more widespread distribution. Restricted today only to the south-central coast of Cuba and adjacent Isla de Pinos, fossils referable to this species have been found in Quaternary deposits in Cuba (Varona, 1984), Grand Cayman (Morgan et al., 1993), and the Bahamas (Olson et al., 1990; Franz et al., 1995; Steadman et al., 2007). Based on this, we might ask some questions such as: was C. rhombifer present in the other Greater Antilles? Did the arrival of C. rhombifer replaced an extant group of endemics? Only more fossils will help answer these question.

Crocodylus rhombifer, photographed at the National Zoo, Washington, DC.

So, there it is, a summarized version of what is known about Cenozoic crocodylians from the Caribbean region. Additional, much older crocs are known from the Jurassic of Cuba, but I'll leave those for a future post.

References

Berg, D. E. 1969. Charactosuchus kugleri, eine neue Krokodilart aus dem Eozän von Jamaica. Eclogae Geologicae Helvetiae 62:731-735.

Bickelmann, C. & N. Klein. 2009. The late Pleistocene horned crocodile Voay robustus (Grandidier & Vaillant, 1872) from Madagascar in the Museum für Naturkunde Berlin. Fossil Record 12(1):13-21.

Brochu, C. A. 2006. A new miniature horned crocodile from the Quaternary of Aldabra Atoll, Western Indian Ocean. Copeia 2006(2):149-158.

Brochu, C. A. 2007a. Morphology, relationships, and biogeographical significance of an extinct horned crocodile (Crocodylia, Crocodylidae) from the Quaternary of Madagascar. Zoological Journal of the Linnean Society 150:835-863.

Brochu, C. A. 2007b. Systematics and taxonomy of Eocene tomistomine crocodylians from Britain and northern Europe. Palaeontology 50(4):917-928.

Brochu, C. A. & A. D. Rincon. 2004. A gavialoid crocodylian from the Lower Miocene of Venezuela. Special Papers in Palaeontology 71:61-78.

Brochu, C. A., A. M. Nieves-Rivera, J. Vélez-Juarbe, J. D. Daza-Vaca & H. Santos. 2007. Tertiary crocodylians from Puerto Rico: evidence for late Tertiary endemic crocodylians in the West Indies? Geobios 40:51-59.

Domning, D. P. & J. M. Clark. 1993. Jamaican Tertiary marine Vertebrata; pp. 413-415 in R. M. Wright & E. Robinson (eds.), Biostratography of Jamaica. Boulder Colorado, Geological Society of America Memoir 182.

Franz, E. F., G. S. Morgan, N. Albury & S. D. Buckner. 1995. Fossil skeleton of a Cuban crocodile (Crocodylus rhombifer) from a blue hole on Abaco, Bahamas. Caribbean Journal of Science 31:149-152.

Gasparini, Z. 1968. Nuevos restos de Rhamphostomopsis neogaeus (Burm.) Rusconi 1933, (Reptilia, Crocodilia) del “Mesopotamiense” (Plioceno Medio-Superior) de Argentina. Ameghiniana 5:299-311.

Jouve, S., M. Iarochene, B. Bouya and M. Amaghzaz. 2006. New material of Argochampsa krebsi (Crocodylia: Gavialoidea) from the Lower Paleocene of the Uolad Abdoun Basin (Morocco): phylogenetic implications. Geobios 39:817-832.

Jouve, S., N. Bardet, N.-E. Jalil, X. Pereda Suberbiola, B. Bouya & M. Amaghzaz. 2008. The oldest African crocodylian: phylogeny, paleobiogeography, and differential survivorship of marine reptiles through the Cretaceous-Tertiary boundary. Journal of Vertebrate Paleontology 28(2):409-421.

Kraus, R. 1998. The cranium of Piscogavialis jugaliperforatus n. gen., n. sp. (Gavialidae, Crocodylia) from the Miocene of Peru. Paläontologische Zeitchrift 72:389-406.

Langston, W. 1965. Fossil crocodilians from Colombia and the Cenozoic history of the Crocodilia in South America. University of California Publications in Geological Sciences 52:1-152.

Langston, W. & Z. Gasparini. 1997. Crocodilians, Gryposuchus, and the South American gavials; pp.113-154 in R. F. Kay, R. H. Madden, R. L. Cifelli & J. J. Flynn (eds.), Vertebrate Paleontology in the Neotropics: the Miocene fauna of La Venta, Colombia. Smithsonian Institution, Washington, DC.

MacPhee, R. D. E. & A. R. Wyss. 1990. Oligo-Miocene vertebrates from Puerto Rico, with a catalog of localities. American Museum Novitates 2965:1-45.

Morgan, G. S., R. Franz & R. I. Crombie. 1993. The Cuban crocodile, Crocodylus rhombifer, from Late Quaternary fossil deposits on Grand Cayman. Caribbean Journal of Science 29:153-164.

Olson, S. L., G. K. Pregill & W. B. Hilgartner. 1990. Studies on fossil and extant vertebrates from San Salvador (Watlings) Island, Bahamas. Smithsonian Contributions to Zoology 508:1-15.

Riff, D. & O. A. Aguilera. 2008. The world’s largest gharials Gryposuchus: description of G. croizati n. sp. (Crocodylia, Gavialidae) from the Upper Miocene Urumaco Formation, Venezuela. Paläontologische Zeitchrift 82:178-195.

Sill, W. 1970. Nota preliminar sobre un nuevo gavial del Plioceno de Venezuela y una discusión de los gavialis Sudamericanos. Ameghiniana 7:151-159.

Steadman, D. W., R. Franz, G. S. Morgan, N. A. Albury, B. Kakuk, K. Broad, S. E. Franz, K. Tinker, M. P. Pateman, T. A. Lott, D. M. Jarzen & D. L. Dilcher. 2007. Exceptionally well preserved late Quaternary plant and vertebrate fossils from a blue hole on Abaco, The Bahamas. Proceedings of the National Academy of Sciences 104(50):19897-19902.

Varona, L. S. 1984. Los cocodrilos fósiles de Cuba (Reptilia: Crocodylidae). Caribbean Journal of Science 20:13-18.

De la tierra al agua

2009-04-26T13:07:00.017-04:00

Algunos de los mamíferos marinos que existen hoy día, como los cetáceos, sirénidos y pinípedos*, están tan adaptados a una vida en el agua, que puede que se nos haga difícil relacionarlos con sus parientes más cercanos los cuales son terrestres. Aquí les voy a dar un poco de información sobre la evidencia que existe hasta ahora sobre la trancición de la tierra al agua en estos grupos de organismos.

*(cetáceos = ballenas y delfines; sirénidos = manatí y dugong; pinípedos = focas, morsas y leones marinos).

Cetáceos

Las ballenas que conocemos hoy día se pueden dividir en dos grupos, los odontocetos y misticetos. Los odontocetos se caracterizan por tener dientes y utilizar ecolocalización; los misticetos se caracterizan por tener barbas en lugar de dientes (ambos grupos tienen otras adaptaciones que discutiré en otro momento). Ejemplos de odontocetos son las orcas y delfines; las misticetos incluyen ballenas azules y ballenas pigmeas.

Estudios moleculares idicaban que las ballenas evolucionaron de los artiodáctilos – grupo que incluye a los cerdos, hipopótamos, camellos, vacas, ovejas, etc – (Graur & Higgins, 1994; Shimamura et al., 1997). Estudios morfológicos solían indicar que los cetáceos habían evolucionado de los mesoniquios – un grupo extinto de mamíferos terrestres carnívoros – (Luo & Gingerich, 1999). En parte, la razón para que existiera esa discrepancia sobre los orígenes de los cetáceos era que los fósiles de cetáceos más antiguos consistían de formas ya completamente adaptadas a una vida en el agua, o solamente se conocía el cráneo. Ya esto ha sido resuelto.

En el 2001, dos grupos de paleontólogos publicaron trabajos donde describían fósiles de ballenas primitivas, incluyendo partes del postcráneo que demostraban que estas estaban relacionadas a los artiodáctilos (Gingerich et al., 2001; Thewissen et al., 2001). Gingerich y su equipo recuperaron los restos de dos Artiocetus clavis y Rhodocetus balochistanensis, mientras que el grupo de Thewissen recuperaron los de Ichthyolestes pinfoldi y Pakicetus attocki (ilustración adyacente de Pakicetus por Carl Buell, tomado de la página del Thewissen Lab); entre las partes que encontraron incluía uno de los huesos del tobillo, el astrágalo, que fue la pieza clave para determinar que los cetáceos evolucionaron de los artiodáctilos. Todos estos fósiles fueron encontrado en sedimentos que datan del Eoceno Medio (entre 49 y 41 millones de años). Recientemente, Thewissen et al. (2007) describen los restos postcraneales del artiodáctilo primitivo, Indohyus, y demuestran que este era un animal con adaptaciones acuáticas y provee evidencia adicional sobre el origen de los cetáceos. (Una reconstrucción magnífica de Indohyus puede ser vista aquí.)

Sirénidos

Los parientes vivos más cercanos de los manatíes y dugones son los elefantes, esto está evidenciado tanto por información morfológica como genética (Seiffert, 2007; Tabuce et al. 2007). EL origen de los sirénidos fue en África alrededor de 54 millones de años donde compartieron un ancestro en común con los elefantes. Interesantemente, los fósiles de sirénidos más primitivos se han encontrado en Jamaica, lo cual demuestra que muy temprano en su historia evolutiva ya estaban adaptados a una vida en ambientes marinos. Durante mucho tiempo, el sirénido fósil más primitivo era Prorastomus sirenoides encontrado en Jamaica en depósitos que datan de 51-49 millones de años (Owen, 1855; Savage et al., 1994). Sin embargo, el postcráneo de este organismo todavía sigue siendo desconocido.

Otro sirénido fósil, también de Jamaica, pero encontrado en depósitos un poco más jovenes (49-45 millones de años), fue descrito por Domning (2001). Este nuevo fósil, llamado Pezosiren portelli (ilustración arriba tomada de Domning, 2001), consiste de partes del cráneo y postcráneo. Los restos postcraneales de Pezosiren incluye los brazos, patas, pelvis y casi toda la columna vertebral; en conjunto, estos indican que este organismo era capaz de soportar su cuerpo fuera del agua a la misma vez, también tiene adaptaciones acuáticas como costillas agrandadas y densas y la fosa nasal retractada (Domning, 2001). Esta combinación de adaptaciones indican que este organismo pasaba tiempo tanto dentro como fuera del agua.

Pinípedos

Estudios morfológicos y moleculares demuestran que los pinípedos pertenecen a un grupo de mamíferos llamado arctoideos (Deméré et al., 2003), que además de los pinípedos, incluyen a los osos (úrsidos), mustelas (mustélidos), mapaches (prociónidos) y zorrilos (mefítidos) entre otros. Sin embargo, el origen de los pinípedos de alguno de estos otros arctoideos no es clara y diferentes estudios ponen a los pinípedos originándose de un ancestro en común con los mustélidos o con los úrsidos (Deméré et al., 2003). Otros expertos en la materia apoyan la idea que los pinípedos tienen origenes separados, las focas evolucionando de un ancestro en común con los mustélidos y los leones marinos y morsas con los úrsido (Uhen, 2007 y referencias ahí). Cualquiera que sea el grupo del cual los pinípedos se originaron, algo que solo se podrá aclarar a medida que se descubren más fósiles, sabemos que se originan de un organismo terrestre. Interesantemente, fósiles de pinípedos que demuestren una morfología transicional, entre completamente marino / completamente terrestre, no fueron encontrados hasta hace poco.

El reciente descubrimiento de Puijila darwini en sedimentos lacustrinos depositados entre 23-21 millones de años, nos da una idea sobre la morfología de los primeros pinípedos (Rybczynski et al., 2009). Aunque ya se han econtrado restos de pinípedos más antiguos, Enaliarctos tedfordi y E. barnesi encontrados en rocas que datan de entre 28.5-23.8 en Oregon (Deméré et al., 2003), estos ya presentan adaptaciones a una vida marina como las que vemos en las especies modernas, lo cual significa que los pinípedos deben haber evolucionado previo a esta fecha. Así que aunque Puijila (ilustración adyacente tomada de Rybczynski et al., 2009) es más joven, su importancia resta en que su morfología es la más primitiva de los pinípedos conocidos, proveyendo además evidencia sobre los posibles pasos evolutivos que se llevaron a cabo en la transición de la tierra al agua en este grupo de mamíferos.

Gracias a MPT y YFS por ayudar con la gramática.

Página oficial de Puijila

Puijila en National Geographic

English version here.

Referencias

Deméré, T. A., A. Berta & P. J. Adams. 2003. Pinnipedomorph evolutionary biogeography. Bulletin of the American Museum of Natural History 279:32-76.

Domning, D. P. 2001. The earliest known fully quadrupedal sirenian. Nature 413:625-627.

Gingerich, P. D., M. ul Haq, I. S. Zalmout, I. H. Khan & M. S. Malkani. 2001. Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan. Science 293:2239-2242.

Graur, D. & D. G. Higgins. 1994. Molecular evidence for the inclusion of cetaceans within the order Artiodactyla. Molecular Biology and Evolution 11(3):357-364.

Owen, R. 1855. On the fossil skull of a mammal (Prorastomus sirenoides, Owen), from the island of Jamaica. Quarterly Journal of the Geological Society of London 11:541-543.

Rybczynski, N., M. R. Dawson & R. H. Tedford. 2009. A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia. Nature 458:1021-102.

Seiffert, E. R. 2007. A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic, morphological, and fossil evidence. BMC Ecolutionary Biology 7:224 Open access

Thewissen, J. G. M., E. M. Williams, L. J. Roe & S. T. Hussain. 2001. Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature 413:277-281.

Thewissen, J. G. M., L. N. Cooper, M. T. Clementz, S. Bajpai & B. N. Tiwari. 2007. Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature 450:1190-1195.

Uhen, M. D. 2007. Evolution of marine mammals: back to the sea after 300 million years. Anatomical Record 290:514-522.

Domningia and other Indian sirenians

2009-04-03T10:44:00.005-04:00

Over the last 12 years a number of fossil sirenians have been described from Eocene through Miocene deposits from India. This has not stopped as, new taxa are been discovered and described; much of the effort is spearheaded by Sunil Bajpai of the Dept. of Earth Sciences, Indian Institute of Technology and J. G. M. Thewissen of the Dept. of Anatomy and Neurobiology, NEOUCOM (Thewissen Lab). So far all the fossil sirenians from India have been collected from outcrops in the Kachchh District near the western coast of the country; this area is better known for primitive cetaceans such as remingtonocetids (Kumar & Sahni, 1986).

Eocene

The oldest Indian sirenians come from the Middle Eocene Harudi Formation; a total of three species representing two families: Protosiren sp. (Protosirenidae), Eotheroides babiae, Eosiren sp. (Dugongidae, Halitheriinae) (Bajpai et al. 2006). Other species belonging to those genera are found in Eocene deposits in northern Africa (Domning, 1996) indicating a southern Tethyan influence, better referred to as the Indo-African Region of the Tethys Realm (Harzhauser et al. 2002). There should be more on Eocene sirenians from India, sometime this year.

Oligocene

So far only one Oligocene sirenian is known from this region, Bharatisiren indica (Dugongidae, Dugonginae) from the Maniyara Fort Formation of Late Oligocene age (Bajpai et al. 2006). This is the oldest dugongine found in this region, and it is as old as the dugongines, Crenatosiren olseni and Dioplotherium manigualti from the Western Atlantic (Domning, 1989; Domning, 1997) and a new taxon from Puerto Rico. Dugongines are a group that is thought to have evolved in the Western Atlantic and Caribbean Region (Domning, 2001), the occurrence of B. indica seems to point to a latest Eocene or Early Oligocene origin for the group with subsequent trans-Atlantic dispersal to the Indo-African Region. An alternative scenario, is the origin of dugongines in the Mediterranean region of the Tethys Realm with subsequent east and west dispersal, unfortunately no Early or Late Oligocene dugongines are known from this region (the names of the paleobiogeographic areas based on Harzhauser et al. 2002).

Lateral view of the skull of B. indica from Bajpai et al. (2006).

Miocene

During the Early Miocene there seems to have been a radiation of dugongines in this region. With at least two taxa known Bharatisiren kachchhense, Domningia sodhae* from Khari Nadi Formation (Bajpai & Domning, 1997; Thewissen & Bajpai, 2009), and another currently under study, it is an good example of multispecies communities like the ones present in the Western Atlantic and Caribbean Region (Domning, 2001). As you can see in the composite picture below, a notable difference between B. kachchhense and Domningia sodhae is the rostral deflection, which probably reflects different degrees of specializations for bottom feeding (Domning, 2001). They seem to have had similar shape of their tusks, large and more-or-less oval in cross-section, this morphology most likely aided in obtaining large seagrass rhizomes (Domning, 2001; Domning & Beatty, 2007), although probably at different levels due to the differences in rostral deflection. Interestingly, it seems that there were no post-Eocene halitheriines.

*Domningia sodhae was aptly named after Dr. Daryl P. Domning of Howard University, world renowned paleosirenologist, a well deserved recognition.

Lateral view of B. kachchhense (top; from Bajpai & Domning, 1997) and Domningia sodhae (bottom; image reversed, from Thewissen & Bajpai, 2009).

Where are the halitheriines?

So far no post-Eocene halitheriines are known from the Oligocene and Miocene of India, at least two possible explanations come to mind: (1) they were present but no fossils have been found yet, or; (2) they were totally absent. An explanation for the second alternative could be provided by the invertebrate fauna. Based on gastropod fauna it seems that, during the Oligocene, changes in the geological settings in the Tethys Realm led to changes in the ocean currents and what was previously known as the Indo-African Region was subsequently divided into the Mediterranean-Iranian and Western Indian-Eastern African provinces of the Western Tethyan Region (Harzhauser et al. 2002). Subsequently, during the Early Miocene, further fragmentation of the Western Indian-Eastern African Province led to an increase of South-East Asian influence and the formation of the Proto-Western Indian Ocean Province; this separation was further augmented by the closure of the Eastern Mediterranean seaway during the latest Early Miocene (Harzhauser et al. 2002). The progressive isolation of what would become the Proto-Western Indian Ocean Province from a Tethyan influence might have prevented halitheriines from entering the region, especially after the Late Oligocene, leading to specialization and radiation of dugongines in this part of the world.

References

Bajpai, S. & D. P. Domning. 1997. A new dugongine sirenian from the Early Miocene of India. Journal of Vertebrate Paleontology 17(1):219-228.

Bajpai, S., J. G. M. Thewissen, V. V. Kapur, B. N. Tiwari & A. Sahni. 2006. Eocene and Oligocene sirenians (Mammalia) from Kachchh, India. Journal of Vertebrate Paleontology 26(2):400-410.

Domning, D. P. 1989. Fossil Sirenia of the West Atlantic and Caribbean Region. II. Dioplotherium manigaulti Cope, 1883. Journal of Vertebrate Paleontology 9:415-428.

Domning, D. P. 1996. Bibliography and index of the Sirenia and Desmostylia. Smithsonian Contributions to Paleobiology 80:1-611.

Domning, D. P. 1997. Fossil Sirenia of the West Atlantic and Caribbean Region. VI. Crenatosiren olseni (Reinhart, 1976). Journal of Vertebrate Paleontology 17:397-412.

Domning, D. P. 2001. Sirenians, seagrasses, and Cenozoic ecological change in the Caribbean. Palaeogeography, Palaeoclimatology, Palaeoecology 166:27-50.

Domning, D. P. & B. L. Beatty. 2007. Use of tusks in feeding by dugongid sirenians: observations and tests of hypotheses. The Anatomical Record 290:523-538.

Harzhauser, M., W. E. Piller & F. F. Steininger. 2002. Circum-Mediterranean Oligo-Miocene biogeographic evolution – the gastropods’ point of view. Palaeogeography, Palaeoclimatology, Palaeoecology 183:103-133.

Kumar, K. & A. Sahni. 1986. Remingtonocetus harudiensis, new combination, a Middle Eocene Archeocete (Mammalia, Cetacea) from western Kutch, India. Journal of Vertebrate Paleontology 6(4):326-349.

Thewissen, J. G. M. & S. Bajpai. 2009. A new Miocene sirenian from Kutch, India. Acta Palaeontologica Polonica 54(1):7-13.

Solenodon paradoxus grooved incisors

2009-03-19T11:22:00.004-04:00

Keeping up with the previous post, here’s a picture of the mandible of a Hispaniolan Solenodon. Notice that I have made an enlargement of the anterior part, outline in the top picture, to show the groove present on its second incisor. The red lines outline the borders of the groove. The specimen was collected in the Dominican Republic and is in the collection of the Department of Paleobiology at the National Museum of Natural History.

Answers to the mystery critter post

2009-03-09T12:04:00.007-04:00

Congratulations to Ville Sinkkonen for guessing correctly the identity of the Marabou stork (Leptoptilos crumeniferus) and the genus of the mystery critter 2, which actually is the Hispaniolan solenodon (Solenodon paradoxus) (full pictures below). I must apologize for taking sooo long in posting the answers, but I’m also adding some interesting facts about this critters, enjoy!!

Marabou storks are scavengers, but will also consume frogs, fish and mice; when stalking prey they rely mainly on their vision, but if needed also by tactolocation (Kahl, 1966). One observation made by Kahl (1966), is that along with other birds, marabou storks will wait near brushfires for escaping or injured prey. The skulls of an interesting group of pterosaurs, the azhdarchids, has been likened to marabou storks and other terrestrial stalkers, which together with other morphological evidence has implication for their paleoecology (Witton & Naish, 2008). More on those interesting pterosaurs here.

In addition to Leptoptilos crumeniferus from sub-Saharan Africa, there are two other species known, Leptoptilos javanicus from South East Asia and L. dubius from South Asia. An extinct larger form, Leptoptilus falconeri, from the Pliocene of Africa and South Asia, stood up to about 2 meters and might have been more terrestrial (had proportionately slightly smaller wings) (Louchart et al. 2005). Other fossil species include L. titan from the Pleistocene of Java and L. richae from the Late Miocene of Tunisia, additional species that have been recognize in the past from Asia or Africa have been synonimized mainly with L. falconeri (Louchart et al. 2005). More recently, Noriega & Cladera (2008) described Leptoptilos patagonicus from the Late Miocene of Argentina. This South American record expands not only the range of the genus, but also of the tribe Leptoptilini (op. cit.). It wouldn’t be surprising if these turn out in similar or younger age deposits around western and/or northern South America.

Now on to Solenodon. There are only two extant species of solenodons, Solenodon paradoxus and S. cubanus from Hispaniola and Cuba respectively. According to studies on gene sequences of these living species, they seem to have diverged about 76 million years ago from their common ancestor with other eulipotyphlan insectivores, whereas divergence between the two species seem to have occurred about 25 million years ago (Roca et al. 2004). An interesting aspect of the dentition of Solenodon paradoxus is that one of the lower incisors (I₂) has a groove on the lingual side (here), which in the living animal serves for injecting venom (McDowell, 1958). This makes S. paradoxus the only known living mammal with modified dentition for venom delivery. Although this could be used to infer similar adaptation in extinct mammals, caution should be taken when finding extinct mammals with grooved dentition, as the sole presence of a grooved canine or incisor should not be regarded as a definite indication of capabilities of injecting venom into victims (Folinsbee et al. 2007, Orr et al., 2007). If you’re interested in the cranial osteology Solenodon paradoxus there’s a recent publication, Wible (2008), which is very detailed and has very good illustrations.

The fossil record of Solenodon shows that there were at least two other species during the Pleistocene, S. marcanoi and S. arredondoi from Hispaniola and Cuba respectively (Patterson, 1962; Morgan & Ottenwalder, 1993). Older remains, consisting of part of an axial skeleton, were found embedded in amber from the Early to Middle Miocene La Toca Formation of the Dominican Republic; these were described as belonging to a small solenodontid insectivore by MacPhee & Grimaldi (1996).

Solenodon, was not the only insectivore living in the Caribbean region, there was also a closely related form that was found in Cuba, Hispaniola and Puerto Rico, these were the Nesophontes (McDowell, 1958), which will be the subject of a future post.

REFERENCES

Folinsbee, K. E., J. Müller & R. R. Reisz. 2007. Canine grooves: morphology, function, and relevance to venom. Journal of Vertebrate Paleontology 27(2):547-551.

Kahl, M. P. 1966. Comparative ethology of the Coconiidae. Part 1. The marabou stork, Leptoptilos crumeniferus (Lesson). Behaviour 27(1-2):76-106.

Louchart, A., P. Vignaud, A. Likius, M. Brunet & T. D. White. 2005. A large extinct marabou stork in African Pliocene hominid sites, and a review of the fossil species of Leptoptilos. Acta Palaeontologica Polonica 50(3):549-563.

MacPhee, R. D. E. & D. A. Grimaldi. 1996. Mammal bones in Dominican Amber. Nature 380:489-490.

McDowell, S. B., Jr. 1958. The Greater Antillean Insectivores. Bulletin of the American Museum of Natural History 115:113-214.

Morgan, G. S. & J. A. Ottenwalder. 1993. A new extinct species of Solenodon (Mammalia: Insectivora: Solenodontidae) from the Late Quaternary of Cuba. Annals of the Carnegie Museum 62(2):151-164.

Noriega, J. I. & G. Cladera. 2008. First record of an extinct marabou stork in the Neogene of South America. Acta Palaeontologica Polonica 53(4):593-600.

Orr, C. M., L. K. Delezene, J. E. Scott, M. W. Tocheri & G. T. Schwartz. 2007. The comparative method and the inference of venom-delivery systems in fossil mammals. Journal of Vertebrate Paleontology 27(2):541-546.

Patterson, B. 1962. An extinct solenodontid insectivore from Hispaniola. Breviora 165:1-11.

Roca, A. L., G. K. Bar-Gal, E. Eizirik, K. M. Helgen, R. Maria, M. S. Springer, S. J. O’Brien & W. J. Murphy. 2004. Mesozoic origin for West Indian insectivores. Nature 429: 649-651.

Wible, J. R. 2008. On the cranial osteology of the Hispaniolan Solenodon, Solenodon paradoxus Brandt, 1833 (Mammalia, Lipotyphla, Solenodontidae). Annals of the Carnegie Museum 77(3):321-402.

Witton, M. P. & D. Naish. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleoecology. PLoS ONE 3(5):1-16.

Identify the mystery critters/Identifica los animales misteriosos

2009-02-12T21:00:00.004-05:00

It’s been a while since I posted something, mostly because of a class that takes away most of my daytime productive hours. So, here’s a brief post on which you will have to figure out what are the critters in the pictures. I’ll be traveling during the weekend but will hopefully have some time to finish a longer post I have been working on, sporadically, for the last month or so. Feel free to post your identification.

Enjoy the pictures and, by the way, Happy Darwin Day!!!

Hace tiempo que no “posteo” nada, mayormente debido a una clase que tengo durante mis horas productivas del día. Asi que aquí tienen una entrada breve donde ustedes tratarán de identificar los animales en las fotos. Estaré viajando durante el fin de semana, pero espero sacar tiempo para terminar una entrada un poco más extensa en la cual he estado trabajando esporádicamente durante el último mes. Siéntanse libre de comentar sobre la identificación.

Disfruten las fotos y felíz día de Darwin!!!

Mystery critter 1/animal misterioso 1

Mystery critter 2/animal misterioso 2

A river runs through an Oligocene sea

2009-01-15T11:40:00.013-05:00

The subject of this post is about my second and final day of fieldwork in Puerto Rico. Yes, I only managed to get two days of fieldwork because these were actually some very short vacations and on top of that it was very rainy. Anyways, I already wrote about my first day of fieldwork during which I searched for tetrapods in the Late Oligocene Lares Limestone. Now on my second day I went out to one of my favorite localities, herein referred to as Río G. This locality consists of exposures of the Early Oligocene age San Sebastián Formation along the banks of a river (See the picture below with me as scale and outcrops on each side of the river). The exposures along this river are considered as typical of the basal part of this formation (Monroe, 1980). The lithology of this formation is varied, with some layers representing ancient soils, river channels, deltaic deposits as well as marine units. Of course this is all in a sequence that makes sense with the tectonic history and paleogeography of the region, an interesting subject, which I will not touch at this moment, but might be discussed sometime in the future.

Now, some interesting tetrapods have been recovered from this formation, such as the sirenian Caribosiren turneri, described by Reinhart in 1959. Also from this formation are known pelomedusid turtles, which were previously discussed here. From the Río G locality, one of the more recent discoveries is the skull of the gryposuchine gavialid Aktiogavialis puertoricensis (Velez-Juarbe, et al. 2007). Other tetrapods found here, include sirenians, part of a croc axial skeleton and the oldest-but-crappiest rodent fossil from the Caribbean region. Some of these, like the sirenians are part of my thesis project, whereas the others are still awaiting description or for better material to turn up.

Unfortunately, same as with the prospecting in the Lares Limestone, no new or even useful vertebrate fossils were found in Río G. The most interesting fossil I found was a plant fossil that might be a seed or some sort of fruit (see picture below of the seed/fruit together with a schematic drawing – the fossil measures about 27 mm across). If it actually turns out to be a seed/fruit it would not be the first time that plant “megafossils” are found in the San Sebastián Formation; about 88 taxa of plant macrofossils from this formation were described by Sir Arthur Hollick in the 1920’s (Graham, 1996). I have yet to see Hollick’s (1926, 1928) papers; therefore I still don’t know if my fossil is similar to any of the material he described.

Well, at least since Río G is along a body of water, it turned out a nice place to do some bird watching. I have on previous occasions observed some of the birds along this river, with the difference that now I had a camera with a good zoom allowing me to take some nice pictures. The composite picture below include, clockwise beginning with the upper left: male Molothrus bonariensis (shiny cowbird); Butorides striatus (green-backed heron); Egretta caerulea (little blue heron); Actitis macularia (spotted sandpiper, this one has the winter plumage hence the lack of spots).

An interesting fact about the shiny cowbird is that it is an invasive species from South America, first reported from the Caribbean region during the latter half of the 1800’s (Post & Wiley, 1977a). It is also a brood parasite; in Puerto Rico it parasitizes about 16 different species of birds with a preference for the yellow-shouldered blackbird (Agelaius xanthomus) (Post & Wiley, 1977b; Pérez-Rivera, 1986). These are actually bad news as the yellow-shouldered blackbird is an endemic to the Puerto Rico bank.

On the earlier half of the day, while stalking a green-backed heron (Butorides striatus), I was unwillingly reminded to always keep an eye of where I put my feet. The reason was that while trying to stealthily sneak up to see where the bird was standing, I almost ended up stepping on a couple of fairly large green iguanas (Iguana iguana) (see composite picture below)!

This was actually the first time I have seen green iguanas in the wild in this part of the island. Iguanas are an introduced pest in Puerto Rico therefore their occurrence in this locality took me totally by surprise, although I am aware that they are getting more common around the island, specially in the east and north where it is more humid (I believe they are still not present in the drier southern coast or that they are much less common there). Green iguanas are doing really well in Puerto Rico; the reason might be that once they reach an adult size, nothing, except maybe humans, will eat them. Perhaps another reason for their success is that until several thousand years ago there were Anegada rock iguanas (Cyclura pinguis) in Puerto Rico (Pregill, 1981); are then green iguanas just filling in an empty niche left over by the extinction of the Anegada rock iguana from Puerto Rico? This is unlikely; rock iguanas (Cyclura spp.) are adapted to xeric environments, which, unlike today, were present in northern PR during the Pleistocene (Pregill & Olson 1981). This means that the habitat that was occupied by C. pinguis in northern Puerto Rico, no longer exist there (rock iguanas are not the only xeric-adapted tetrapod to go extinct in northern PR [op. cit.]). All I know is that from now on I will have to keep an eye out for green iguanas while doing fieldwork, at least in northern Puerto Rico.

References

Graham, A. 1996. Paleobotany of Puerto Rico-from Arthur Hollick’s (1928) scientific survey paper to the present. Annals of the New York Academy of Sciences 776: 103-114.

Hollick, A. 1926. Fossil walnuts and lignite from Porto Rico. Journal of the New York Botanical Garden 27:223-227.

Hollick, A. 1928. Paleobotany of Porto Rico. Scientific Survey of Porto Rico and the Virgin Islands 7(3):177-393.

Monroe, W. H. 1980. Geology of the middle Tertiary formations of Puerto Rico. US Geological Survey Professional Paper 953:1-93.

Pérez-Rivera, R. A. 1986. Parasitism by the shiny cowbird in the interior parts of Puerto Rico. Journal of Field Ornithology 57(2):99-104.

Post, W. & J. Wiley. 1977a. The shiny cowbird in the West Indies. Condor 79:119-121.

Post, W. & J. Wiley. 1977b. Reproductive interactions of the shiny cowbird and the yellow-shouldered blackbird. Condor 79:176-184.

Pregill, G. K. 1981. Late Pleistocene herpetofaunas from Puerto Rico. University of Kansas Museum of Natural History, Miscellaneous Publications 71:1-72.

Pregill, G. K. & S. L. Olson. 1981. Zoogeography of the West Indian vertebrates in relation to Pleistocene climatic cycles. Annual Review of Ecology and Systematics 12:75-98.

Reinhart, R. H. 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36(1):1-146.

Velez-Juarbe, J., C. A. Brochu & H. Santos. 2007. A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a nonmarine reptile. Proceedings of the Royal Society B 274:1245-1254.

Publicaciones de fósiles de Puerto Rico / Publications on fossils from Puerto Rico

2009-01-05T08:08:00.006-05:00

Para esta nota he recopilado un listado de publicaciones que tratan sobre fósiles de Puerto Rico. Por supuesto que el listado está viciado a favor de publicaciones sobre vertebrados fósiles los cuales son mis favoritos o invertebrados con los cuales he trabajado en el pasado. Si conoces referencias adicionales me puedes avisar (a través de correo electrónico o comentarios abajo) para asi añadirlos a la lista. Algunas de las referencias incluso están enlazados su pdf gratis.

For this post I have compiled a list of publications that deals with fossils from Puerto Rico. Of course it is somewhat biased toward vertebrates, which are my favorites or invertebrates on which I have worked on previous occasions. If you know additional references that are not here just let me know (either through emails or comments below) and they will be added. Some of these are linked to their free pdf.

Anthony, H. E. 1916. Preliminary diagnosis of an apparently new family of insectivores. Bulletin of the American Museum of Natural History 35(41):725-728.

Anthony, H. E. 1917a. New fossil rodents from Porto Rico, with additional notes on Elasmodontomys obliquus Anthony and Heteropsomys insulans Anthony. Bulletin of the American Museum of Natural History 37(4):183-190.

Anthony, H. E. 1917b. Two new fossil bats from Porto Rico. Bulletin of the American Museum of Natural History 37(19):565-568.

Anthony, H. E. 1918. The indigenous land mammals of Porto Rico, living and extinct. American Museum of Natural History, Memoirs 1(2):329-435.

Auffenberg, W. 1967. Notes on West Indian tortoises. Herpetologica 23(1):34-44.

Bold, W. A., Van Den. 1965. Middle Tertiary Ostracoda from Northwestern Puerto Rico. Micropaleontology 11(4):381-414.

Brochu, C. A., A. M. Nieves-Rivera, J. Velez-Juarbe, J. D. Daza-Vaca and H. Santos. 2007. Tertiary crocodylians from Puerto Rico: evidence for late Tertiary endemic crocodylians in the West Indies? Geobios 40:51-59.

Choate, J. R. and E. C. Birney. 1968. Sub-recent Insectivora and Chiroptera from Puerto Rico, with the description of an new bat of the genus Stenoderma. Journal of Mammalogy 49(3):400-412.

Cutress, B. M. 1980. Cretaceous and Tertiary Cidaroida (Echinodermata, Echinoidea) of the Caribbean area. Bulletin of American Paleontology 77:1-221.
Domning, D. P. and O. A. Aguilera. 2008. Fossil Sirenia of the West Atlantic and Caribbean region. VIII. Nanosiren garciae, gen. et sp. nov. and Nanosiren sanchezi, sp. nov. Journal of Vertebrate Paleontology 28(2):479-500.

Flemming, C. and R. D. E. MacPhee. 1999. Redetermination of holotype of Isolobodon portoricensis (Rodentia, Capromyidae), with notes on recent mammalian extinctions in Puerto Rico. American Museum Novitates 3278:1-11.

Frank, E. F. and R. Benson. 1998. Vertebrate paleontology of Mona Island, Puerto Rico. Journal of Cave and Karst Studies 60:103-106.

Gaffney, E. S., and R. C. Wood. 2002. Bairdemys, a new side-necked turtle (Pelomedusoides: Podocnemididae) from the Miocene of the Caribbean. American Museum Novitates 3359:1-28.

Gordon, W. A. 1963. Middle Tertiary echinoids of Puerto Rico. Journal of Paleontology 37(3):628-642.

Graham, A. 1996. Paleobotany of Puerto Rico-from Arthur Hollick’s (1928) scientific survey paper to the present. Annals of the New York Academy of Sciences 776: 103-114.

Graham, A. and D. M. Jarzen. 1969. Studies in neotropical botany. I. The Oligocene communities of Puerto Rico. Annals of the Missouri Botanical Garden 56:308-357.

Hollick, A. 1926. Fossil walnuts and lignite from Porto Rico. Journal of the New York Botanical Garden 27:223-227.

Hollick, A. 1928. Paleobotany of Porto Rico. Scientific Survey of Porto Rico and the Virgin Islands 7(3):177-393.

Howell, B. F. 1966. New Upper Cretaceous sponge from Puerto Rico. Journal of Paleontology 40(1):207-209.

Iturralde-Vinent, M. A. and E. Harstein. 1998. Miocene amber and lignitic deposits in Puerto Rico. Caribbean Journal of Science 34:308-312.

MacPhee, R.D.E. and M.A. Iturralde-Vinent. 1995. Origin of the Greater Antillean land mammal fauna, 1: new Tertiary fossils from Cuba and Puerto Rico. American Museum Novitates 3141:1-31.

MacPhee, R. D. E. and A. R. Wyss. 1990. Oligo-Miocene vertebrates from Puerto Rico, with a catalog of localities. American Museum Novitates 2965:1-12.

Matthew, W. D. 1916. New sirenian from the Tertiary of Porto Rico. Annals of the New York Academy of Sciences 27:23-29.

McFarlane, D. A. 1999. Late Quaternary fossil mammals and last occurrence dates from caves at Barahona, Puerto Rico. Caribbean Journal of Science 35(3-4):238-248.

Mitchell, S. F., M. Martínez-Colón, R. Ramsook and H. Santos. 2012. A primitive tube-bearing antillocaprinid rudist bivalve, Parasarcolites sohli, sp. nov., from Jamaica and Puerto Rico, West Indies. Cretaceous Research 34:149-153.

Moussa, M. T. 1974. Tertiary brachiopods from Puerto Rico and their paleontologic and paleoecologic significance. Journal of Paleontology 48(6):1202-1206.

Nieves-Rivera, A.M., M. Ruiz-Yantín and M.D Gottfried. 2003. New record of the Lamnid shark Carcharodon megalodon from the Middle Miocene of Puerto Rico. Caribbean Journal of Science 39:223-227.

Olson, S. L. 1976. Fossil woodcocks: an extinct species from Puerto Rico and an invalid species from Malta (Aves:Scolopacidae: Scolopax). Biological Society of Washington, Proceedings 89(20):265-274.

Olson, S. L. 1982. A new species of palm swift (Tachornis: Apodidae) from the Pleistocene of Puerto Rico. The Auk 99:230-235.

Olson, S. L. and E. J. Maíz López. 2008. New evidence of Ara autochthones from an archeological site in Puerto Rico: a valid species of West Indian macaw of unknown geographic origin (Aves: Psittacidae). Caribbean Journal of Science 44(2):215-222.

Olson, S. L. and M. C. McKitrick. 1981. A new genus and species of emberizine finch from Pleistocene cave deposits in Puerto Rico (Aves: Passeriformes). Journal of Vertebrate Paleontology 1(3/4):279-283.

Olson, S. L. and Á. M. Nieves-Rivera. 2010. Fossil evidence and probable extinction of the greater fishing bat Noctilio leporinus (Chiroptera: Noctilionidae) on Isla de Mona, Puerto Rico. Mastozoología Neotropical 17(1):167-170.
Pearson, P. N. and B. S. Wade. 2009. Taxonomy and stable isotope paleoecology of well-preserved planktonic foraminifera from the uppermost Oligocene of Trinidad. Journal of Foraminiferal Research 39(3):191-217.

Pessagno, E. A., Jr. 1963. Planktonic Foraminifera from the Juana Diaz Formation, Puerto Rico. Micropaleontology 9(1):53-60.

Pessagno, E. A., Jr. 1963. Upper Cretaceous Radiolaria from Puerto Rico. Micropaleontology 9(2):197-214.

Pisera, A., M. Martínez and H. Santos. 2006. Late Cretaceous siliceous sponges from El Rayo Formation, Puerto Rico. Journal of Paleontology 80(3):594-600.

Pregill, G. K. 1981. Late Pleistocene herpetofaunas from Puerto Rico. University of Kansas Museum of Natural History, Miscellaneous Publications 71:1-72.

Rabell-Cabrero, N. 1914. Notas paleontológicas. Revista de las Antillas 2(1):66-69.

Rabell-Cabrero, N. 1924. Notas sobre algunos escuálidos fósiles de Puerto Rico. Revista Agricultura de Puerto Rico 12:377-384.

Reinhart, R. H. 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36(1):1-146.

Schweitzer, C. E., M. A. Iturralde-Vinent, J. L. Hetler and J. Velez-Juarbe. 2006. Oligocene and Miocene Decapods (Thalassinidea and Brachyura) from the Caribbean: Annals of the Carnegie Museum of Natural History 75(2):111-136.

Schweitzer, C. E., J. Velez-Juarbe, M. Martinez, A. Collmar Hull, R. M. Feldmann and H. Santos. 2008. New Cretaceous and Cenozoic decapoda (Crustacea: Thalassinidea, Brachyura) from Puerto Rico, United States Territory. Bulletin of the Mizunami Fossil Museum 34:1-15.

Sohl, N. F. 1992. Upper Cretaceous gastropods (Fissurellidae, Haliotidae, Scissurellidae) from Puerto Rico and Jamaica. Journal of Paleontology 66(3):414-434.

Sohl, N. F. 1998. Upper Cretaceous trochacean gastropods from Puerto Rico and Jamaica. Palaeontographica Americana 60:1-109.

Turvey, S. T. 2010. Evolution of non-homologous venom delivery systems in West Indian insectivores? Journal of Vertebrate Paleontology 30(4):1294-1299.

Turvey, S. T., F. V. Grady and P. Rye. 2006. A new genus and species of ‘giant hutia’ (Tainotherium valei) from the Quaternary of Puerto Rico: an extinct arboreal quadruped? Journal of Zoology 270:585-594.

Turvey, S. T., J. R. Oliver, Y. M. Narganes Storde and P. Rye. 2007. Late Holocene extinction of Puerto Rican native land mammals. Biology Letters 3:193-196.

Velez-Juarbe, J. and D. P. Domning. 2011. A new dugongine (Sirenia; Dugongidae) from the late Oligocene of Puerto Rico and its position within the Dugonginae. Abstracts Sixth Triennial Conference on Secondary Adaptation of Tetrapods to Life in Water, p. 77.

Velez-Juarbe, J. and T. E. Miller. 2007. First report of a Quaternary Crocodylian from a cave deposit in Northern Puerto Rico. Caribbean Journal of Science 43(2):273-277.

Velez-Juarbe, J. and H. Santos. 2008. Fossil Echinodermata from Puerto Rico; pp. 369-395 in W. I. Ausich and G. D. Webster (eds.), Echinoderm Paleobiology. Indiana University Press, Bloomington, Indiana.

Velez-Juarbe, J., C. A. Brochu and H. Santos. 2007. A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a nonmarine reptile. Proceedings of the Royal Society B, 274:1245-1254.

Wetmore, A. 1920. Five new species of birds from cave deposits in Porto Rico. Biological Society of Washington, Proceedings 33:76-81.

Wetmore, A. 1922. Bird remains from the caves of Porto Rico. Bulletin of the American Museum of Natural History 46:297-333.

Williams, E. E. 1952. A new fossil tortoise from Mona Island, West Indies and a tentative arrangement of the tortoises of the world. Bulletin of the American Museum of Natural History 99(9):541-560.

Williams, E. E. and K. F. Koopman. 1951. New fossil rodent from Puerto Rico. American Museum Novitates 1515:1-9.

Wood, R. C. 1972. A fossil pelomedusid turtle from Puerto Rico. Breviora 392:1-13.

Woods, C. A. 1996. The land mammals of Puerto Rico and the Virgin Islands. Annals of the New York Academy of Sciences 776:131-149.

Among old corals & living spiders…

2008-12-28T09:09:00.006-05:00

The winter holidays means that other than getting a break from the university I also get to go home where it is warmer than DC, get some good coffee and also get to do some fieldwork. But so far this has been a very unproductive field season. The weather has been very unstable with rain almost everyday, which is very unusual for this period of the year as it is supposed to be drier.

On the only good day of fieldwork so far, I went to a couple of road cuts in the northwest where the Lares Limestone of Late Oligocene age is exposed. These outcrops are very good and have produced so far, fishes (both bony and cartilaginous), sirenians (which are part of my thesis), unidentified crocodylians (described in Brochu et al. 2007), and pelomedusid turtles, which I mentioned in an older post. Invertebrates are also found, among them the crustaceans, which have been recently described (Schweitzer et al. 2006) and corals, which are well known and well preserved (Frost et al., 1983; Edinger & Risk, 1994). Picture below shows a close-up of a Montastrea sp. (left) and a large overturned coral (right).

Now that you have a general idea of what can be found in the Lares Ls, lets get back to my fieldwork; this time around the prospecting in these limestones was not the best. The only non-fish remains were an incomplete neural plate, most likely from a pelomedusid turtle and a large croc tooth. As I mentioned above crocs have been reported from the Lares Ls, nonetheless in contrast to the ones previously reported, this recent find (see picture below) differs from the ones described previously which are smaller, slender and similar to the ones found in longirostrine crocs (Brochu et al. 2007). This larger tooth is the third tooth of this type found in this formation, the other two already in the paleo collection a the Department of Geology at UPR-Mayagüez. Finding such teeth is actually a big tease, as they seem to indicate that during Lares time there were other crocs in addition to an unknown longirostrine form. That there might have been a longirostrine form during Lares time should not be a surprise, one species is already known from the underlying San Sebastián Formation of Early Oligocene age. The species, called Aktiogavialis puertoricensis, is related to South American gharials and together they form a monophyletic group called Gryposuchinae (Velez-Juarbe et al. 2007 [free pdf here]). As you see it should come as no surprise that there might have been a longirostrine croc during Lares time, but who was the owner of the other large teeth? A crocodyloid? An alligatoroid? There must have been something other than a longirostrine croc, but only by finding better specimens will this question be answer.

Croc teeth from the Lares Ls: the one on the left is similar to those reported in Brochu et al. (2007), the tooth on the right is the recent find notice the size & shape differences (scale bar = 1 cm).

I almost forgot about the spiders, well, since the fossil collecting was so crappy, the trip was at least good for taking photos of spiders that are found in this outcrop (see composite picture below). Notably among those are the southern black widows (Latrodectus mactans), one of the three species of black widows known to occur in Puerto Rico (Pérez-Rivera, 1980). This is one of the few outcrops where I really have to keep an eye out for these spiders, as they are very common here. The others are the silver argiope (Argiope argentata) and an orb weaver (Leucauge regnyi). So, enjoy the pictures and have a happy holiday!

References

Brochu, C. A., Á. Nieves-Rivera, J. Vélez-Juarbe, J. D. Daza-Vaca & H. Santos. 2007. Tertiary crocodylians from Puerto Rico: evidence for late Tertiary endemic crocodylians on the West Indies? Geobios 40:51-59.

Edinger, E. N. & M. J. Risk. 1994. Oligocene-Miocene extinctions and geographic restriction of Caribbean Corals: roles of turbidity, temperature, and nutrients. Palaios 9(6):576-598.

Frost, S. H., J. L. Harbour, D. K. Beach, M. J. Realini & P. M. Harris. 1983. Oligocene reef tract development, southwestern Puerto Rico. Sedimenta 9:1-144.

Pérez-Rivera, R. A. 1980. Distribución geográfica, potencial reproductivo y enemigos naturales de la viuda negra en Puerto Rico. Caribbean Journal of Science 15(3-4):79-82.

Schweitzer, C. E., M. Iturralde-Vinent, J. L. Hetler & J. Velez-Juarbe. 2006. Oligocene and Miocene decapods (Thalassinidea and Brachyura) from the Caribbean. Annals of the Carnegie Museum 75(2):111-136.

What’s wrong with the hands of Steller's sea cow

2008-12-12T00:00:00.012-05:00

When talking about species driven to extinction in historic times we automatically think of the Dodo, Carolina Parakeet, Tasmanian tiger, Caribbean monk seal among others. We might as well think of the Steller’s sea cow, Hydrodamalis gigas (picture below of one of the specimens at the NMNH).

H. gigas was a sirenian (sea cows: manatees & dugongs) that lived in the northern Pacific until about 240 years ago. This was one of the largest sea cows that have lived, only surpassed by Hydrodamalis cuestae from the Late Pliocene of California, which is estimated to have reaches up to 9.03 meters (~30 feet!) whereas one of the H. gigas measured by Steller (the first person to describe live specimens) was about 7.51 meters (~25 feet) (Domning, 1978).

The picture below is of a mounted skeleton of H. gigas at the Museum National d’Histoire Naturelle in Paris. It is most likely specimen A.14516, which is the only mounted skeleton at the MNHNP (Mattioli & Domning, 2006). It is a nice mount, but there is something wrong with it……

Look at the hand/flipper, its huge, and very dugong or manatee like (see the more detailed picture below). You see, G. W. Steller was one of the few persons to give an account of H. gigas from observing live (or recently killed) specimens (and hence the name Steller’s sea cow). His description of the hand is significant because the morphology is unlike that of any other known sirenian (Steller, 1899). According to Steller’s description, the forelimb of H. gigas had no fingers, in fact he describes the ends of the limb as having a posteriorly oriented hook-like structure made up of, most likely, stratified squamous keratinized epithelium (thickened hardened skin). The habitat of H. gigas were shallow waters where feeding would have exposed them to higher wave action, therefore the loss of fingers as well as having a hardened pad or surface would have provided more traction when using the forelimbs as propulsion or stabilization in these shallower waters. Domning (1978) concluded from the osteology and inferred myology that additional forelimb adaptations are also present in H. gigas. These adaptations such as reduction of some muscles and modifications to the elbow joint, made the limb better suited for movement in a more parasagittal direction (Domning, 1978).

To sum it all up, Hydrodamalis gigas had no fingers, it also had other forelimb adaptations that permitted it to “walk” in shallow marine substrates when feeding. The Paris mount is nice, but wrong, in that it has huge flippers instead of fingerless stumps.

Domning, D. P. 1978. Sirenian evolution in the North Pacific Ocean. University of California Publications in Geological Sciences 118:1-176.

Mattioli, S. & D. P. Domning. 2006. An annotated list of extant skeletal material of Steller’s sea cow Hydrodamalis gigas (Sirenia: Dugongidae) from the Commander Islands. Aquatic Mammals 32:273-288.

Steller, G. W. 1899. The beasts of the sea. (Translated by W. and J. E. Miller); pp. 179-218 in D. S. Jordan (ed.), The fur seals and fur-seal islands of the North Pacific Ocean. Part 3, Article 8. Government Printing Office, Washington, DC.

Fossil side-necked turtles from Puerto Rico

2008-11-29T21:51:00.000-05:00

As I have learned through my many fieldtrips around Puerto Rico one of the most common fossils in the Tertiary rocks are fragments of turtle shells. In fact one of the first vertebrate fossils I collected (back in 2001) was a turtle shell from the Juana Díaz Formation (Early Oligocene age), which is now in the paleo exhibit at the Geology Museum at the Department of Geology, University of Puerto Rico, Mayagüez Campus. As I latter found out this fossil represented a shell of a pelomedusoid turtle, more commonly known as side-necked turtles (image below of Podocnemis expansa taken at the Museo de Historia Natural Javier Prado in Lima, Perú). Nonetheless it wasn’t the first time that fossil side-necks or other kinds of turtles were found as fossils in Puerto Rico.

One of the first accounts about fossil turtles from Puerto Rico is found in Rabell-Cabrero (1914) where he briefly mentions the occurrence of turtle costal and neural plates among other vertebrate remains that he had collected. This material was collected in Salto Collazo in the town of San Sebastián (northwestern PR), which means that the fossils came from Oligocene age rocks (Rabell-Cabrero, 1914; MacPhee & Wyss, 1990). Most of the vertebrate material collected by Rabell-Cabrero was later donated to the American Museum of Natural History (MacPhee & Wyss, 1990).

Some of the Rabell-Cabrero material was subsequently described by Wood (1972). In this paper Wood describes a shell, plastron and pelvis collected from the San Sebastián Formation (Early Oligocene age) but due to the incompleteness of the material no binomial was given, although similarities with living and extinct South American pelomedusids were noted (Wood, 1972).

In the late 1980’s an expedition from the AMNH recovered side-necked fossils from Early Miocene deposits in northern PR including a shell, proximal humerus and pubis (MacPhee & Wyss, 1990). Although, as they mention, the material is well preserved, a proper description is still pending. This might be in part because the conservative shell morphology of most pelomedusoids makes identification below family level difficult (Gaffney & Zangerl, 1968; Wood & Diaz de Gamero, 1971; MacPhee et al. 2003).

More recently a pelomedusoid skull from Puerto Rico was described by Gaffney & Wood (2002). This skull is now the type species of Bairdemys harsteini, a new genus that also includes three species from Venezuela, B. venezuelensis (formerly known as Podocnemis venezuelensis Wood & Diaz de Gamero, 1971), B. sanchezi and B. winklerae (Gaffney & Wood, 2002; Gaffney et al. 2008). Bairdemys harsteini was collected from Early Miocene deposits of the Cibao Formation in northern Puerto Rico, in addition to the skull, some shell fragments collected by MacPhee & Wyss (1990) from a nearby locality have been referred to this taxon (MacPhee et al. 2003). One interesting aspect of the Venezuelan species B. venezuelensis is that the shells do not have neural bones in the carapace, which might be an autapomorphy of that taxon (the carapace of the other Venezuelan species is still unknown) as neurals seem to be present in the shell material assigned to B. harsteini (Wood & Diaz de Gamero, 1971; Gaffney & Wood, 2002; Gaffney et al., 2008).

Now going back to the Juana Díaz pelomedusoid I mentioned at the beginning, this shell, although missing approximately the anterior half, does have preserved the last three neurals, and seems to have been approximately the same size as the material described by Wood (1972). No additional material from the Juana Díaz or San Sebastián formations has been collected recently (at least not by me or anyone else that I know of). Most of the turtle material I have collected lately actually comes from the Lares Limestone (Late Oligocene age-northern PR). So far the best material from the Lares Ls seems to be from side-necks as well and fairly similar in size and morphology to the Juana Diaz and San Sebastián forms (see drawing comparing these with a Cuban shell mentioned below). Additional preparation (one plastron is still in a plaster jacket and a shell is in a carbonate concretion) might give more information as to whether they represent the same unknown taxon.

More fossil side-necks are known from the Caribbean region, such as Caribemys oxfordiensis from the Jurassic of Cuba, an unknown pelomedusoid from the Early Miocene of Cuba, as well as the many species from Colombia and Venezuela including the largest freshwater turtle Stupendemys geographicus.

Gaffney, E. S. & R. C. Wood. 2002. Bairdemys, a new side-necked turtle (Pelomedusoides: Podocnemididae) from the Miocene of the Caribbean. American Museum Novitates 3359:1-28.

Gaffney, E. S. & R. Zangerl. 1968. A revision of the chelonian genus Bothremys (Pleurodira: Pelomedusidae). Fieldiana Geology 16:193-239.

Gaffney, E. S. T. M. Scheyer, K. G. Johnson, J. Bocquentin & O. A. Aguilera. 2008. Two new species of the side necked turtle genus, Bairdemys (Pleurodira, Podocnemididae), from the Miocene of Venezuela. Paläontologische Zeitschrift 82(2):209-229.

MacPhee, R. D. E. and A. R. Wyss. 1990. Oligo-Miocene vertebrates from Puerto Rico, with a catalog of localities. American Museum Novitates 2965:1-45.

Rabell-Cabrero, N. 1914. Notas paleontológicas. Revista de las Antillas 2(1):66-69.

Wood, R. C. 1972. A fossil pelomedusid turtle from Puerto Rico. Breviora 392:1-13.

Wood, R. C. & M. L. Diaz de Gamero. 1971. Podocnemis venezuelensis, a new fossil pelomedusid (Testudines, Pleurodira) from the Pliocene of Venezuela and a review of the history of Podocnemis in South America. Breviora 376:1-23.

2008-11-29T21:35:00.000-05:00

Welcome to my blog, here I will post about fossils (mostly vertebrates) from the Caribbean region as well as other extinct critters that I find interesting. I’ll post mostly in English, but sometimes also en Español. Sometimes I might just blog about random subjects. So, once again welcome and enjoy.