Back to the western Caribbean, Pt. 3

This will be, for now, the final part of this series. This is going to be a bit of a tease, as I'll go over some of the cetacean find we've made in the last several months won't go into many details as to what each of the fossils are. That will be the subject of future posts, once the fossils are properly described and published. There are a good amount of pictures to make up for it, so enjoy!

Trash road cetacean
As you may have read previously (here, here and here) collecting fossil vertebrates in the Chagres Formation is not an easy task and takes some planning before collecting each specimen. Back in the summer I found what seemed to be the remains of a fossil cetacean partially exposed on on the wave cut platform (see pictures below). To get to this locality we had to walk through a 10 meter stretch of road that is always full of trash, hence the locality name. As for the fossils, not a lot of it was exposed, and the day when we found it, we were on another mission. So we ended going back to the site to collect the fossils two days before Thanksgiving Day, and like most other digs here, we only had about four hours before the high tide took over.

Left: The exposed fossil; right: Chris (Summer 2013 intern) looking at it somewhat in disbelief. 

Finally, in November we collected the fossil. James and I started digging the trench around the fossil, soon after the other interns joined the digging party.

Zach, Sarah, Elena and James (Fall 2013 interns) are happily posing with the jacketed fossil, it only took us about 2 and a half hours. 

And liftoff!! We take the jacket to the truck and off to STRI where it will be properly prepared.

Chagres Norte dolphin
Back in early September, I had the chance to go prospecting in the Chagres Formation with two of my colleagues from invertebrate paleontology at the Florida Museum of Natural History, Roger Portell and Austin Hendy. They've previously done some more work in the marine units here in Panama, so it was good to go out with them and see new localities. One of these, was located further north of the village of Piña than I'm used to. Getting there involved a really muddy road, fortunately, we had all terrain vehicles, and it was actually fun driving through it.

The site, which I dubbed Chagres Norte, was one of the northern-most localities near the village of Piña.

At this site as with others along this whole coast, the Chagres Formation is exposed along the wave-cut platforms and sea cliffs. One of the fossils we knew was there (Roger and Austin had found it some days earlier) was part of the vertebral column of a small cetacean.

Elena (Fall 2014 intern), Roger and Austin collect the cetacean vertebrae. This is one of the reasons I like these guys, even of they specialize in invertebrates, they know not to ignore vertebrate fossils and will collect them.

This was Elena's second day in the field. She got hooked on the Chagres and even "claimed" the fossil saying that she was going to do the prep work, which she did.

The partial vertebral column we collected back in September. This is after Elena's careful and fantastic prep job.

Chagres Sur odontocete
Later that day, we went to another locality, this one south of Piña, so I gave it the obvious name of Chagres Sur. At this site I spotted some cetacean fossils sticking out of the sea cliff (see picture below).

One of the localities south of Piña, where I spotted some cetacean bones (you can see the bones towards the center right). For reasons I can't remember, Elena is staring in the wrong direction.

At that point, I didn't know what this fossil was, and we were also running out of daylight, so we left it there, and hoped to come back another day to collect it. It wasn't until a couple of weeks ago (1st week of December), that I decided to re-visit the locality with the interns. It was then, upon seeing this fossil again, that I had one of those, aha! moments and I realized what it was. So we had to collect it!

Here I am with the Chagres Sur odontocete, just before we removed it.

I won't go into details of what the fossil is at this moment (I warned you this was a post to spark your curiosity). But, if you plan on attending the 10th North American Paleontological Convention in Florida next February, you'll definitely find out more about it!

So stay tuned, you'll hear more about these discoveries in 2014!

Back to the western Caribbean, Pt. 2

The previous post was to give you a brief introduction into the geology of the Chagres Formation, which is where we are focusing part of our collecting efforts. This next post is to give you an idea of what happens when we find fossils of large marine vertebrates in the Chagres.

Often, when we find fossils in the Chagres these are on the rock exposed in the wave-cut platform along the beach (although there are exceptions). The benefit of this is the relatively easy access, the downside, is that we usually have only about 4 hours (spanning between the period before, during and after, the low tide) to collect the fossil. Back in April, during one of our trips to the Caribbean coast, we saw a partial marlin mandible exposed on one of the wave-cut platforms (picture below). That day we were prospecting, that is, looking for new localities and new fossils that were exposed so that we could plan to collect them in the near future. This was one of those finds.

A partial marlin mandible exposed on the wave-cut platform (anterior to the left).

The near future ended up being July. And so it was that together with Carlos De Gracia (a STRI intern whose main interest are fossil fishes), and my summer 2013 interns, Chris, Christina, and Silvia (previously featured here) we set out to the Caribbean to collect that fossil marlin.

Collecting the fossil took us three days. The first day was cut short and we couldn't do much work as the weather turned bad, and we had to leave after about an hour of work. Day two was purely devoted to digging a trench around the fossil so that we could wrap it in a protective plaster jacket for proper removal and transportation back to STRI (see picture below). This is a near obligatory task and method of proper collection of fossil vertebrates and has been used at least  since the late 1800's. While digging around it, we realized that we had more than we thought, the fossil consisted of mandible and skull, which meant we had to dig deeper, and wider around the fossil to be able to remove it completely.

Day 2 of the excavation. From left to right: Carlos De Gracia (STRI intern) and my summer 2013 interns, Christina, Chris and Silvia, make the trench around the marlin skull and mandible.

After we dug a deep enough trench around the fossil, we were ready to put a plaster jacket around it. Except that by then it was late, and the tide was coming back in, meaning we had to jacket the specimen another day. Finally, on our third day at this particular site, were were able to put a jacket around the fossil (see pictures below).

Day 3 of the excavation. Christina and Silvia are finish the jacket protecting the marlin skull and mandible.

This is the locality, if you click on the image you can see Silvia (near the center) and Christina (to the right); behind her is the jacket (the white blob on the ground).

After the plaster dried we undercut the block and flipped it so that we could remove excess rock and make it a bit lighter to carry back to the truck and then drive back to STRI (see pictures below). This specimen, as well as several other marlins that have been collected from the Chagres (including the one mentioned here), will be prepared and studied by Carlos.

After we popped and overturned the jacket,  me, Chris, and Carlos removed some of the excess rock in order to make it lighter.

Liftoff!! Even after trimming some of the rock off, this was still a pretty heavy block.

Other fishes known from the Chagres include a variety of bony fishes (mainly know from otoliths, which I mentioned in Part 1) as well as a several species of sharks (of which cookie-cutter sharks are one of the most common). Marlins are also relatively common and easy to recognize in the field; in fact, this year alone, we have collected several other skulls, mandibles and vertebrae.

Because they are common, the fossil marlins of the Chagres have not gone unnoticed, unlike the marine mammals. In 1978, Harry L. Fierstine described the first fossil marlin known from Panama. The fossil, consisting of a nearly complete skull, represented a new species, which he named Makaira panamensis. Modern relatives of Makaira panamensis include the black and the blue marlins. A second fossil marlin from Panama was described in 1999 (Fierstine, 1999). This one was found in the late Miocene Gatun Formation, which underlies the Chagres Fm. The fossil consisted of a partial rostrum, and was identified as Makaira cf. M. nigricans, the same species as the blue marlin (Fierstine, 1999). This implies that this particular species has been around for several million years, or more likely, that some extant members of this group are morphologically conservative and show very little differences from its fossil relatives.  

I'm sure we'll learn more about the fossil fishes of the Chagres and Gatun formations in the not so distant future. For now, stay tuned as this series is not yet over!

Literature Cited

Fierstine, H. L. 1978. A new marlin, Makaira panamensis, from the Late Miocene of Panama. Copeia 1978:1-11.

Fierstine, H. L. 1999. Makaira sp., cf. M. nigricans Lacépede, 1802 (Teleostei: Perciformes: Istiophoridae) from the Late Miocene, Panama, and its probable use of the Panama Seaway. Journal of Vertebrate Paleontology 19:430-437.

New Title Banner!!

After a few years, I thought it was fair to change the look of the blog a little bit. If you look up I've changed the banner, to one thats better (I think) and less crowded than the previous one. The pictures on the new title banner are all from different localities I've been doing fieldwork over the last couple of years and expect to continue to do so.

As for the old one, here's what was in it.

1) Pleistocene beach deposits in Isabela, Puerto Rico

2) Illustration of the skull of a new dugongid taxon (more on this in 2014)

3) Portunid crab from the San Sebastian Formation

4) Cross-bedded sandstones of the San Sebastian Formation

5) Tooth of Physogaleus contortus from the Lares Limestone

6) Tooth of Hemipristis serra from the Juana Diaz Formation

7) Outcrop of the Lares Limestone along road 111 in San Sebastian, Puerto Rico

8) Illustration of the skull of Dugong dug on showing the muscle attachment sites, modified from Domning (1977)

9) Mandible of Nesophontes edithae, one of several extinct Pleistocene mammals from PR 

Of course, feel free to guess where the pictures in the new banner were taken and leave your comments below. Good luck!!

Back to the western Caribbean, Pt. 1

Its been quite a while since the last post here at Caribbean Paleobiology. Lots of traveling and working hard on publishing parts of my dissertation as well as my current research projects here in Panama (stay tuned for more on this next year) have kept me extremely busy.

As I have mentioned previously, my work during this postdoc requires that I lead a group of interns (you can learn more about the internship here) as we search for terrestrial vertebrates in early Miocene deposits exposed on the Pacific side of the Panama Canal (see previous post). However, every now and then, as you may have seen in previous posts (here and here), we get to go to the Caribbean side of Panama in search of late Miocene marine vertebrates in the Chagres Formation. This is the first part of a series about our recent efforts to collect fossil marine vertebrates and to better understand the geology of the Chagres Fm.

Map of the northern part of the Panama Canal Basin. Here you can see the extension of the Chagres Formation and its members (map from Collins et al., 1996). (Click on the image to see a larger version.)

The Chagres Formation
This formation, exposed on the northern part of the Panama Canal Basin (see map above), generally consist of three distinct members or facies: Toro Member, silty sandstone facies, and Rio Indio facies (Collins et al., 1996). Age estimates for the deposition of the Chagres have been made using Foraminifera (which are extremely good index fossils). As a result, we known that the formation was deposited between 8.6-5.6 million years ago (Collins et al., 1996), during the final part of a geologic period known as the Miocene.

Toro Point, located southwest of the Caribbean exit of the Panama Canal, located within Ft. Sherman, which is a former US military base.

The Toro Member is the basal unit of the formation, and consist of cross-bedded coquinas and medium to coarse sands (see picture below). Coquina, is a term used to describe a sedimentary deposit that consists mostly, if not entirely, of shell fragments. In the case of the Toro Member, it is made up almost entirely of echinoid (sea urchin) and barnacle fragments, together with other less common bivalves and gastropods. Both, the types of invertebrates that make up the coquina, as well as the cross-bedding is indicative of high-energy, shallow marine habitats (Hendy, 2013)

Cross beds of the Toro Member, as exposed in Toro Point.

Disregarding what the geology and macroinvertebrates suggest, the Toro Member has been interpreted as being deposited at much deeper depths (several hundreds of meters), by a high-energy stream flowing from the Pacific Ocean towards the Caribbean sea, and thus representing the final connection between these two oceans (Collins et al., 1996). This interpretation, is based on the occurrence of deep-water fossils of Pacific affinities within the silty sandstone facies.

The silty sandstone facies of the Chagres Formation, as exposed in Playa Tortuguilla, located northeast of Fuerte San Lorenzo, and the mouth of the Chagres River. From left to right: James, Sarah, Elena and Zach (Fall 2013 interns) are studying the trace fossils of the Chagres. 

About 4-5 kilometers southwest of Toro Point, is where the main part of the Chagres Formation, the silty sandstone facies, is exposed. This is the most extensive of the members, going from southwest of Toro Point to about ~6 kilometers southwest of the village of Piña. Foraminifera (or forams for short) are not only used for estimating when marine units were deposited, but can also serve as index fossils for depositional depth, and environment. Forams collected from the silty sandstone facies of the Chagres were used for estimating the depth of this part of the formation, resulting in an estimate of somewhere between 200-500 meters (Collins et al., 1996).

Outcrop of the silty sandstone facies of the Chagres Formation near the village of Piña.

Forams are not the only fossils known from these units. Fierstine (1978) described a fossil marlin which he dubbed Makaira panamensis, an extinct species only known from this place and time. Other fossils found in these facies are fish otoliths. Otoliths are fish ear bones; they can be identified fairly accurately, and, similar to forams, they can be used as index fossils. A preliminary study of the otolith fauna of the silty sandstone facies collected near the village of Piña, suggests that these facies were deposited somewhere between 100-700 meters (De Gracia et al., 2012). This is a broader estimate, than that obtained using the forams, but still consistent with the idea that the silty sandstone facies represent relatively deep marine environments. These units, have so far, proven to be the most productive in terms of vertebrate fossils, thus most of our efforts have been in this area. In fact, back in 2011, I was near Piña, collecting a fossil dolphin* as part of the Pyenson Lab, and, more recently, with the Spring 2013 interns we collected a fossil sperm whale and parts of a marlin skull. (More about even more recent discoveries in the following iterations of this series).
*You can see more of the fossil dolphin collected during the Pyenson Lab 2011 expedition here!

Outcrop of the Río Indio facies of the Chagres Formation, somewhere south of La Boca del Indio. 

Towards the southwest, along the opposite site of the basin, between Palmas Bellas and Rio Gobea, is where we find the Rio Indio facies. These facies are characterized by siltstones and sandstones (Collins et al., 1996). Estimates of the depositional environment of these facies are variable, but generally much shallower than those of the silty sandstone facies (see below). Based on forams, it ranged from 50-80 meters, whereas estimates based on fish otoliths (= fish ear bones) it ranges from 0-100 meters (Collins, 1996; Collins et al., 1996; Aguilera and Aguilera, 1999). Just today was our first time visiting some of the Río Indio localities, and although we didn't find any vertebrates, we did find mollusks which are consistent with the shallower depth interpretations of previous workers.

So, stay tuned for the upcoming installments of this series!


Literature Cited

Aguilera, O., and D. R. de Aguilera. 1999. Bathymetric distribution of Miocene to Pleistocene Caribbean teleostean fishes from the coast of Panama and Costa Rica. Bulletins of American Paleontology 357:251-270.

Collins, L. S. 1996. Environmental changes in Caribbean shallow waters relative to the closing Tropical American Seaway; pp. 130-167, in J. B. Jackson, A. Budd, and A. Coates (eds.), Evolution and Environment in Tropical America. University of Chicago Press, Chicago, Illinois.

Collins, L. S., A. G. Coates, W. A. Berggren, M.-P. Aubry, and J. Zhang. 1996. The late Miocene Panama isthmian strait. Geology 24:687-690.

De Gracia, C., J. Carrillo-Briceño, W. Schwarzhans, and C. Jaramillo. 2012. An exceptional marine fossil fish assemblage reveals a highly productive deep-water environment in the Central American Seaway during the late Miocene. Geological Society of America Abstracts with Programs 44:164.

Fierstine, H. L. 1978. A new marlin, Makaira panamensis, from the late Miocene of Panama. Copeia 1978:1-11.

Hendy, A. J. W. 2013. Spatial and stratigraphic variation of marine paleoenvironments in the middle-upper Miocene Gatun Formation, Isthmus of Panama. Palaios 28:210-227.

Updates from Panama

Soon after the last post, I headed out to the US, for a short collection trip. During this trip, I visited both the Florida Museum of Natural History (FLMNH), and the National Museum of Natural History (NMNH) as I needed to compare my notes on some fossil cetaceans from the late Miocene of Panama with material housed in those institutions. It was also an opportunity to see my wife as well as spend some quality time with some good friends.

Gainesville, FL
At the Florida Museum of Natural History, I focused on comparing the Panamanian material with several fossil toothed whales in the collections, mainly from the late Miocene and early Pliocene of Florida. There are some interesting specimens at the FLMNH and I was able to make some useful comparisons. I also took some time to look at the exhibits in the museum, which I had not fully done yet.

Me, pointing out to the Florida dugongid triad, of which I wrote early last year (Vélez-Juarbe, et al., 2012). These are part of one of the exhibits at the Florida Museum of Natural History. Not everyday you get to see fossils you've worked on as part of an exhibit. One of those is a new species, so stay tuned!!

Washington, DC
At the Smithsonian in Washington, DC, I had the opportunity to look at both extant and fossil whales. For this, I went to the Smithsonian's Museum Support Center (MSC) which is where the extant whales are housed. If you study whales and dolphins of any kind, this is the place to go! The collection at the MSC allows us to look at more than one individual of a certain species, which gives us a better understanding of differences in the morphology due to age (juveniles vs adults) or sex (males vs females), or just variation within a species. We need to know this, specially when it comes to describing fossil species.

The "whale warehouse", one of the several storage facilities at the Smithsonian's Museum Support Center. If you need to look at skeletons of extant whales, this is the place to go!

The skull of Bohaskaia monodontoides a fossil beluga which Nick Pyenson and myself described last year (Vélez-Juarbe & Pyenson, 2012). Now part of a temporary exhibit called "Whales: From Bone to Book". Make sure you see it if you're in the DC area, its awesome!!

I also looked at several fossil whales, mostly physeteroids, which is the group that include sperm whales and pygmy sperm whales.

Some of the fossil whale I studied at the NMNH. Left: cast of the skull of Aulophyseter morricei, a small sperm whale from the middle Miocene of California (Kellogg, 1927). Right: the skull of Aprixokogia kelloggi, a fossil pygmy sperm whale from the early Pliocene of North Carolina (Whitmore & Kaltenbach, 2008).

Panama
After the US tour, I returned to Panama. Fieldwork so far, has been pretty standard along the canal. One of the recent highlights, was the visit of Bruce MacFadden, who brought a fantastic group of school teachers from California and Florida. We all did some fieldwork along the canal and also went to some localities of the Gatun Formation. At one of the Gatun localities the teachers had prepared an in situ paleontological workshop for a group of local schoolchildren, which was a wonderful experience for all of us involved!

The students were measuring diversity within a meter square grid.

It was not all fieldwork. We also had the chance to go birdwatching along the Pipeline trail in Gamboa, where we did get to see several birds, as well as a lot of other fauna along the trail.

On our hike along the Pipeline trail, led by George Angehr of the BioMuseo, and also author  of Birds of Panama (an excellent reference).

Some of the fauna we saw along the Pipeline trail. Clockwise from top left: leaf beetle (Platyphora haroldi); brown-throated three-toed sloth (Bradypus variegatus); black-tailed trogon (Trogon melanurus); striped rocket frog (Silverstonneia flotator).

So I guess that's it for now. But stay tuned as more discoveries are made in the canal and elsewhere here in Panama!


References
Kellogg, R. 1927. Study of the skull of a fossil sperm-whale from the Temblor Miocene of southern California. Carnegie Institution of Washington Publication 346:1-23.

Vélez-Juarbe, J., and N. D. Pyenson. 2012. Bohaskaia monodontoides, a new monodontid (Cetacea: Odontoceti: Delphinoidea) from the Pliocene of the Western North Atlantic Ocean. Journal of Vertebrate Paleontology 32:476-484.

Vélez-Juarbe, J., D. P. Domning, and N. D. Pyenson. 2012. Iterative evolution of sympatric seacow (Dugongidae, Sirenia) assemblages in the past ~26 million years. PLoS ONE 7(2):e31294.

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.

Whale Rescue in the Canal

A little more than a month ago I got an email regarding a fossil find near the construction site of the new canal locks on the Atlantic side of Panama. The photo that came with the email was a bit blurry and with no scale, so it could as well be a small fossil, or even an invertebrate. However, I took the chance as it was, after all, an opportunity to look at outcrops on that part of the canal (most of our work is towards the Pacific side). And so it was, that the spring interns (previously featured here and here) and myself ended up driving towards Colón with the hopes that the fossil was some sort of interesting vertebrate.

One thing I must mention, is that security is very tight in the canal, much more so near the construction sites. So that day, we only had about 20 minutes to look at the fossil and eventually come up with a plan to collect it at some later time, if it was worth it.

And it was! Upon seeing the fossil, I immediately recognized it as a baleen whale jaw. Most of what we could see was a cross section of it (see below), which meant that however long the jaw was, it was going straight into the wall.

Part of a baleen whale jaw, in cross section.

It is not the first time that fossil whales have been found in Panama. A 2010 paper by Mark Uhen of George Mason U. and colleagues (including yours truly) described all that was known of the fossil marine mammals of Panama. Admittedly, it wasn't much, but we were able to confirm the presence of dugongid sirenians, toothed whales (odontocetes) and baleen whales (mysticetes) (Uhen et al., 2010).   Since then, more and better material has been found, including a couple of odontocete skulls that I have helped collect from the late Miocene Chagres Formation (see here and here), as well as other things you'll hear about later this year at SVP.

The new whale mandible was found in the Gatun Formation of late Miocene (12-8 Ma) age (Collins et al., 1996). The Gatun is better known for the abundance of invertebrates (e.g. Woodring, 1957; Hendy, 2013) and for having deposits that represent nursery sites for Carcharocles megalodon (Pimiento et al., 2010). Previous reports of whales from the Gatun include odontocete ribs (Uhen et al., 2010), so finding a baleen whale is a first!

Like I mentioned above, that day we only had a very limited amount of time, and the fossil was worth rescuing. And so it was that over the next month or so I began coordinating with the Panama Canal Authority to go back and collect the fossil. Just last week we were able to go back. This time I had a new group of interns, and over the course of two days we were able to collect the fossil.

The summer interns at the dig site. Chris (at far left) prospects, while Christina and Silvia dig around the whale jaw.  You can see the construction of the new locks in the background.

Unfortunately, due to the nature of the outcrop we only had a limited space and depth to dig. So we had to make the best out of it. Sadly, that meant that if the jaw was longer than our depth limit, we had break it.

The whale jaw, prior to being jacketed.

Me posing with the now jacketed whale jaw fragment. 

The exact affinities of the whale jaw remain a mystery, for now. Hopefully once it is prepared I'll be able to determine what it is. So stay tuned!


References

Collins, L. S., A. G. Coates, W. A. Berggren, M.-P. Aubry, and J. Zhang. 1996. The late Miocene Panama isthmian strait. Geology 24:687-690.

Hendy, A. J. W. 2013. Spatial and stratigraphic variation of marine paleoenvironments in the middle-upper Miocene Gatun Formation, Isthmus of Panama. Palaios 28:210-227.

Pimiento, C., D. J. Ehret, B. J. MacFadden, and G. Hubbell. 2010. Ancient nursery area for the extinct giant shark Megalodon from the Miocene of Panama. PLoS ONE 5(5):e10552.

Uhen, M. D., A. G. Coates, C. A. Jaramillo, C. Montes, C. Pimiento, A. Rincón, N. Strong, and J. Velez-Juarbe. 2010. Marine mammals from the Miocene of Panama. Journal of South American Earth Sciences 30:167-175.

Woodring, W. P. 1957. Geology and paleontology of Canal Zone and adjoining parts of Panama. Geology and description of Tertiary mollusks (gastropods: Trochidae to Turritellidae). U.S. Geological Survey Professional Paper 306-A:1-146.

The Southernmost Atlantic Seacows

Its been a while since I posted news on fossil sirenians. I've been very busy with fieldwork, manuscripts, among other things. The Spring interns have now gone back home. So, while I wait for the arrival of the next round of interns, here's the latest on fossil sirenians.


Where are sirenians found

With the exception of the now extinct Steller's seacow (Hydrodamalis gigas), all extant sirenians have tropical to subtropical distribution, with some species having a notably broad latitudinal and longitudinal distribution (Marsh et al., 2011). But, when we look at the fossil record of sirenians, we see a slightly different pattern of distribution, mostly tied to tectonic and/or climatic events. For example, during parts of the Cenozoic global temperatures were higher than today (Zachos et al., 2001), so you find fossils of sirenians far off their modern range (e.g. Belgium). These climatic variations amongst other physical drivers have played a prominent role in the distribution of seagrasses and seacows (expect more on this in the nearby future).

Nowadays, in the Western Atlantic and Caribbean (WAC) region, the most common and widespread sirenian is the West Indian Manatee (Trichechus manatus) whose range extends from as far north as the Carolina's (with some individuals reaching New England) to northeastern Brazil; another species found in the region is the Amazonian manatee (Trichechus inunguis) which lives in the Amazon basin (see map below). But, it hasn't always been like this. Throughout most of the Cenozoic, dugongids, a group of sirenians are now restricted to the Indo-Pacific region, were the predominant seacow group in the WAC, including multispecies communities in the region (Domning, 2001; Velez-Juarbe et al., 2012a; see previous post on this subject). Fossil of dugongids in the WAC are found in deposits as far north as Maryland, and as far south as Argentina. However, these southernmost dugongids, are poorly known, and have had a somewhat rocky taxonomic history.


From Metaxytherium to Dioplotherium a case of mistaken identity

The most common, and temporally and geographically widespread seacow genus known is the Halitheriine dugongid Metaxytherium. Species of this genus are known from late Oligocene through Pliocene deposits, and are found from the Eastern Pacific, Caribbean, Western and Northern Atlantic, and Western Tethys regions (e.g. Domning, 1988; Sorbi et al., 2012). Therefore it shouldn't have been much of a surprise when Roy H. Reinhart (1976) described a molar from the late Miocene Paraná Formation of Entre Ríos, Argentina as that of Metaxytherium. The importance of this find, lies in that prior to its discovery, the youngest species of Metaxytherium known from the WAC was the middle Miocene M. floridanum, which is not known outside of Florida (Domning, 1988). The Paraná molar was then, the youngest and southernmost record of the genus from the Western Atlantic.

However, species of Metaxytherium display a generally conservative morphology, and because of this, it has had a long, somewhat convoluted, taxonomic history. This is, fortunately, slowly being resolved as most species of Metaxytherium have been re-described (e.g. Domning, 1988; Domning & Pervesler, 2001; Sorbi et al., 2012) and studied in detail within the last 25 years, giving us, paleosirenologist a better idea of the valid species within the genus and variation within each species. Since Reinhart's description, several workers (Cozzuol, 1996; Cione et al., 2000; Domning, 2001) have disagreed with his interpretation regarding the affinities of the Argentinian molar. All of them referring the Paraná molar to Dioplotherium, still a dugongid, but one that belongs to the Dugonginae, a group very different from that to which Metaxytherium belongs. And indeed, the overall morphology of the tooth conforms well with what we know about Dioplotherium, it is in fact, very similar to those of Dioplotherium cf. D. allisoni from the early Miocene of Brazil (Toledo & Domning, 1991). This meant that Metaxytherium may have gone extinct in the WAC at the end of the middle Miocene (Domning, 1988), and that the genus only reached as far south as northeastern Brazil (Toledo & Domning, 1991), or did it?

Left: Map showing the distribution of Miocene seacows throughout the Americas. (ER = Entre Ríos).
Right: Map showing the distribution of extant sirenian in the Americas.
(Click on the map to view larger version.)

New fossils from the Paraná Formation

A couple of years ago I received an email from an Argentinian colleague, Jorge Noriega from CONICET in Diamante, informing me of a new discovery from the Paraná Formation in Entre Ríos. The new fossils consisted of left and right partial maxillae and most of the molars of a single individual (see figure below). At this point I was close to finishing my PhD, which meant that I had look at a lot of specimens and was well acquainted with the morphology of most, if not all Oligocene through Pliocene sirenians. Once I looked at the pictures of the new material, I quickly recognize these as most likely representing a species of Metaxytherium.

Molars of Metaxytherium from the late Miocene Paraná Formation. 1-2) left maxilla and M1-3 in occlusal view. 3-4) right maxilla and M3 (modified from Velez-Juarbe et al., 2012b)

Now, I must admit that dugongid teeth are not the most diagnostic, so figuring out if these actually belonged to Metaxytherium was not an easy and quick task. After a considerable amount of reading, and detailed observations of material from various species of Metaxytherium as well as other dugongids I was confident they belonged to that genus. And so, working together with Jorge and Brenda Ferrero (also from CONICET in Diamante) we took on the task of formally re-designating the fossil described by Reinhart (1976) as well as describing the new material which actually represented a species of Metaxytherium (Velez-Juarbe et al., 2012b). The new Parana molars are quite similar to those of the middle Miocene Metaxytherium floridanum, but, their dimensions are below the range exhibited by M. floridanum and may represents a different species. One of the positive outcomes resulting from this work, was realizing that teeth of dugongids can sometimes be of taxonomic usefulness. We noticed, that the molars of some of the more derived species of Metaxytherium often have additional cusp and/or cuspules, a derived character which is not observed in Dioplotherium or any of its kin (i.e. Dugongines). The contemporaneous presence of both, Dioplotherium and Metaxytherium is not something unheard of. This same duet, occurs in the late Oligocene of Florida, early Miocene of Brazil and possibly in the middle Miocene of California and Baja California (Domning, 2001; Velez-Juarbe et al., 2012a). This again shows that multispecies communities and niche partitioning seems to have been the norm, not the exception, throughout sirenian history.


References

Cione, A. L., M. M. Azpelicueta, M. Bond, A. Carlini, J. Casciotta, M. A. Cozzuol, M. de la Fuente, Z. Gasparini, F. Goin, J. Noriega, G. Scilato-Yané, L. Soibelzon, E. Tonni, D. Verzi, and M. G. Vucetich. 2000. Miocene vertebrates from Entre Ríos Province, Argentina. INSUGEO, Serie Correlación Geológica 14:191-238.

Cozzuol, M. A. 1996. The record of the aquatic mammals in southern South America. Münchner Geowissenschaftliche Abhandlungen A30:321-342.

Domning, D. P. 1988. Fossil Sirenia of the West Atlantic and Caribbean region. I. Metaxytherium floridanum Hay, 1922. Journal of Vertebrate Paleontology 8:295-426.

Domning, D. P. 2001. Sirenians, seagrasses, and Cenozoic ecological change in the Caribbean. Palaeogeography, Palaeoclimatology, Palaeoecology 1:27-50.

Domning, D. P., and P. Pervesler. 2001. The osteology and relationships of Metaxytherium krahuletzi Depéret, 1895 (Mammalia: Sirenia). Abhandlungen der Senckenbergischen Naturforschenden Gessellschaft 553:1-89.

Marsh, H. D., T. J. O'Shea, and J. E. REynolds, III. 2011. Ecology and conservation of the Sirenia: dugongs and manatees. Cambridge University Press, 521p.

Reinhart, R. H. 1976. Fossil sirenians and desmostylids from Florida and elsewhere. Bulletin of the Florida State Museum, Biological Sciences 20:187-300.

Sorbi, S., D. P. Domning, S. C. Vaiani, and G. Bianucci. 2012. Metaxytherium subapenninun (Bruno, 1839) (Mammalia, Dugongidae), the latest sirenian of the Mediterranean Basin. Journal of Vertebrate Paleontology 32:686-707.

Toledo, P. M., and D. P. Domning. 1991. Fossil Sirenia (Mammalia: Dugongidae) from the Pirabas Formation (Early Miocene), northern Brazil. Boletim do Museu Paraense Emílio Goeldi, Série Ciencias da Terra 1:119-146.

Velez-Juarbe, J., D. P. Domning, and N. D. Pyenson. 2012a. Iterative evolution of sympatric seacow (Dugongidae, Sirenia) assemblages during the past ~26 million years. PLoS ONE 7(2):e31294.

Velez-Juarbe, J., J. I. Noriega, and B. S. Ferrero. 2012b. Fossil Dugongidae (Mammalia, Sirenia) from the Paraná Formation (late Miocene) of Entre Ríos Province, Argentina. Ameghiniana 49:585-593.

Zachos, J., M. Pagani, L. Sloan, E. Thomas, and K. Billups. 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292:686-693.

Return to the Caribbean side of Panama, pt. 2

A couple of Friday's ago, we were set to return to the locality where we had been excavating a relatively large whale skull. Last time we were there we manage to make the jacket around the skull, but the plaster did not dry quickly enough, and we had to leave it, as it was late in the day and the tide was coming in. Unfortunately, due to the change in time of the low tide (happening later and later in the day) as well as other technical problems, we could not go back as soon as we wanted. So we ended up waiting a whole week to return and hopefully finish the job.

A local girl, Pedro, Nicole and Samantha pose next to the jacket.

To our surprise, the jacket held up during the eight days that passed since we made it. Those were good news as it meant that our work and effort from the previous week was not lost and that we didn't had to make a new jacket. Plaster bandages are hard if not impossible to get here in Panama, so I was extremely happy we didn't had to use more than we already had.

Pedro, a local kid, Erik, Nicole and Samantha happily pose next to the large jacket as we get ready to move it to the truck.

We were able to remove the jacket and get it into our truck without further incidents, this wouldn't have been possible without the interns who are doing a great job! To top it off, we even found another tooth associated with the skull. Its not the first one, Aaron had already collected two, which were somewhat incomplete, but hinted at the affinities of the skull. The new tooth we collected is complete, and I can now confidently say that it belongs to a physeterid (a sperm whale)!! Sperm whales are found nowadays in the Caribbean, but their fossil record in the region is relatively poor, with only a handful of reports from a few sites. So this is a fantastic find!

One of the teeth associated with the skull in the jacket. Notice the large root and small enameled crown (to the left of the photo).

Stay tuned, as I'm sure we'll keep finding many other interesting fossils here in Panama.

Return to the Caribbean side of Panama

As part of the PCP-PIRE we not only get to look for fossils and study the geology of Panama along the canal. We also get to prospect and collect at other localities. Yesterday, we made the two hour drive to the Caribbean side of the country, where late Miocene marine units are exposed along the beach. If this sounds familiar, is because I had been there a couple of years ago, where, as part of the Pyenson Lab we went to collect a really nice fossil dolphin skull.

On our way to the locality we had to go through the Gatún Lock, and wait for several ships to go through before we could cross.

Going to this locality means we have to really plan ahead, as the late Miocene deposits will be best exposed at low tides. That also means that we only have about a four hour window to prospect and collect.

As the water recedes, the rock is exposed and its time to prospect!!

Ideally, we can find and collect specimens on a single day (within that 4 hour window), others may take longer, and require to return to the site one or more additional days.

Here Samantha and Pedro work on a project they stated with Aaron several months ago, excavating a large whale skull.

We worked two sites simultaneously this day. Pedro, Samantha and Erik continued an excavation they started several months ago with Aaron. They are digging around what seems to be a large whale skull. Nicole and I were about 15-20 meters southwest of where they were. We were busy digging what seems to be part of yet another whale skull. The skull seems to be broken or at least there's a skull and postcranial elements associated with it, so we collected these in two jackets (see picture below).

Here we take a break and have some snacks and talk with the local kids while the two small plaster jackets (center of the pictures) dry out so we can remove them and take them back to the lab.

We'll go back today to finish off the large whale skull, and who knows what else we'll find. So stay tuned!

Fossil Mammals of Panama

In recent years the efforts to know the fossil terrestrial vertebrates of Panama have been revitalized, in part thanks to the expansion of the canal and the efforts of Panama Canal Project-PIRE in collaboration with the Panama Canal Authority. Vegetation grows fast in the tropics, so good fossiliferous deposits are covered and basically lost within years, even months, of being exposed. The new cuts being made for the expansion of the canal offer a unique opportunity to further understand the geology and paleontology of the area.
Interest in the fossil vertebrates of Panama started when Robert H. Stewart, a geologist with the Panama Canal Company, alongside his assistant, started finding and collecting fossil vertebrate remains in the early 1960's. The fossils were being collected from sediments of the Cucaracha Formation exposed along the Gaillard Cut, one of the artificial valleys that was crucial to the making of the canal. Frank C. Whitmore Jr. (who sadly passes away a little more than a year ago) was then a paleontologist with the US Geological Survey (and expert on fossil mammals) and eventually got involved with the collecting and studying of the Panamanian fossil. He and Stewart published the results of their study in 1965 (Whitmore & Stewart, 1965). Prior to these discoveries, very little was known of the fossil vertebrate fauna of the Central American region, and these were actually the first Miocene fossils found between Honduras and Colombia (Whitmore & Stewart, 1965). Up to that point it was not known wether Central America had been separated from North or South America (some even said both) during the Cenozoic, and if so, for how long? So the discovery of Miocene terrestrial mammals in Panama was a big deal!

The Gaillard Cut and Centenario Bridge in the early morning.

One of the main results of Whitmore & Stewart's study was that the Miocene Panamanian fauna was of holarctic* affinities. That meant that at least through the early Miocene, Panama was connected to North America, even though its geographically much closer to northwestern South America**. The fauna studied by them consisted of turtles, crocodylians, horses, rhinos, oreodonts and protoceratids (which I mentioned in a previous post). The mammal assemblage of this fauna is very similar to coeval faunas in North America.
*a term used for the biogeographic region comprising the northern continents.
**we now know that they remained separated by a marine passageway known as the Central American Seaway until about 3 million years ago (Duque-Caro, 1990; Coates et al., 1992).

Another closer look at the Gaillard Cut. Here you can see sediments of the Cucaracha Formation with Centenario Bridge in the Background.

The fauna described by Whitmore & Stewart was eventually called the Gaillard Cut Local Fauna (Ferrusquía-Villafranca, 1978; Rich & Rich, 1983; MacFadden, 2006). However, the fossils that make up this fauna had not been described in detail. It wasn't until until Bruce MacFadden of the Florida Museum of Natural History took on the task of describing them, 40 years after they had been collected (MacFadden, 2006). As a result, the composition of the Gaillard Cut Local Fauna has changed due to new discoveries, and will most likely continue to do so in the upcoming years. So, stay tuned as I'll cover this subject on the next post.

*Access to this and all other paleontological localities along the canal brought to you thanks to the courtesy of the Panama Canal Authority (ACP).

References

Coates, A. G., J. B. C. Jackson, L. S. Collins, T. M. Cronin, H. J. Dowsett, L. M. Bybell, P. Jung, and J. A. Obando. 1992. Closure of the Isthmus of Panama: the near-shore marine record of Costa Rica and western Panama. GSA Bulletin 104:814-828.

Duque-Caro, H. 1990. Neogene stratigraphy, paleoceanography and paleobiogeography in northwestern South America and the evolution of the Panama Seaway. Plaeogeography, Palaeoclimatology, Palaeoecology 77:203-234.

Ferrusquía-Villafranca, I. 1978. Distribution of Cenozoic vertebrate faunas in middle America and the problems of migrations between North and South America. Instituto de Geología, Universidad Nacional Autónoma de México 101:193-329.

MacFadden, B. J. 2006. North American Miocene land mammals from Panama. Journal of Vertebrate Paleontology 26:720-734.

Rich, P. V., and T. H. Rich. 1983. The Central American dispersal route: biotic history and paleogeography; pp. 12-34 in D. H. Janzen (ed.), Costa Rican Natural History. University of Chicago Press, Chicago, Illinois.

Whitmore, Jr., F. C., and R. H. Stewart. 1965. Miocene mammals and Central American Seaways. Science 148:180-185.

GSA Southeastern Section Meeting 2013

Just a week and a half ago (March 20-21, 2013) was the 62nd Annual Meeting of the Geological Society Southeastern Section, held in San Juan, Puerto Rico. This two day meeting was a great venue, not only to see some interesting presentations, but was also an opportunity to meet colleagues I had not seen in a while. One of the sessions during the first day was chaired by my friend Alvin Bonilla-Rodríguez of the University of Kansas, and myself. The aim of the session, titled: Multidisciplinary Approaches to Caribbean Stratigraphy and Paleontology, was to find out what our colleagues are up to these days. It was both our first time chairing a session, so we were both a little nervous, but I think it went pretty well. We had a great set of talks as well as poster presentations. Overall it was a fantastic meeting, hat-tip to the organizers for doing such a great job!

The title slide of my GSA talk. 

Of course, going to Puerto Rico for a meeting also meant I would stick around for a few days more.
And so I did. It was time to see my family, but also go to the field and revisit some localities.

Friday after the meeting I returned once again to my favorite early Oligocene locality (see previous posts here, here and here). It hasn't rain a lot in Puerto Rico lately, so the exposure was even better as this locality is exposed along the banks of a river. This gave me the opportunity to spend the morning measuring and describing in detail the main fossiliferous section.

The lowermost marine units was remarkable for the presence of the clam Lucina collazoensis (you can see several of them near the center of the picture). 

Overall, the sequence consists of alternating terrestrial and shallow marine horizons. It is in one of those marine horizons where I have collected several fossil vertebrates, including side-neck turtles, sirenians and rodents among others.

The main part of the section, you can see the terrestrial (brownish-redish units) and the marine (grayish units).

Of course, this wasn't the only day I went to the field. The next day I set out to Ponce, in the southern coast of Puerto Rico, where I will meet with colleagues from the Florida Museum of Natural History, as well as others interested in seeing Oligocene and Miocene marine deposits in that area. It was sort of an unofficial post-meeting field trip.

Our first stop in Ponce, where early Oligocene marine deposits are exposed.

Some of the fossils found at this locality. Left, some crinoid stem fragments. Crinoids were once inhabitants of shallow seas, but since the end of the Paleozoic, they are more typical of deeper settings. Right, a shark tooth, probably a carcharhinid. 

After spending a couple of hours at this locality we were ready to move on to the next outcrop. Unfortunately, my field vehicle would not start, and had to get towed back home.

My field vehicle, acting up...

The others, went on (we were on three vehicles), hopefully they found interesting fossils.

I'm back in Panama (it was a very short trip to PR). So stay tuned for upcoming entries on the geology and paleontology of this beautiful country.