Chevron weirdness in a sirenian

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!

Prep work: update II and a note on sirenian periotics

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.

A day in the field, Tertiary

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.

Field err… lab work

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

There are only a few naturally-ocurring modern species of crocodylians in the Greater Antilles, namely the endemic Cuban crocodile (Crocodylus rhombifer) and the American crocodile (Crocodylus acutus) which is widely distributed throughout the region. Here I briefly summarize what is known so far about the Cenozoic crocodylians of the Caribbean region. 

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-middle Miocene crocodylian remains have been collected in Cuba, Dominican Republic and Puerto Rico (MacPhee & Wyss, 1990; MacPhee et al., 2003; Brochu et al., 2007; Brochu & Jiménez-Vázquez, 2014). The 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 middle Miocene age Cibao Fm (MacPhee & Wyss, 1990; Brochu et al., 2007).  The Cibao fossils include a partial dentary, frontal and partial left squamosal, and show a combination of features that excludes it from being a gavialoid, alligatorid, Crocodylus or any other extant taxon (Brochu et al., 2007). Similarly, there are some unusual crocodylian remains from the early Miocene Lagunitas Formation in Cuba (Brochu & Jiménez-Vázquez, 2014). This implies that at least starting in the early Miocene (and probably even earlier) Puerto Rico, and other islands in the Caribbean , where probably 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. & O. Jiménez-Vázquez. 2014. Enigmatic crocodyliforms from the early Miocene of Cuba. Journal of Vertebrate Paleontology 34:1094-1101.

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.

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.

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. 

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.

Actualizado: 8 de febrero de 2021

Among old corals & living spiders…

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.

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.

Fossil side-necked turtles from Puerto Rico

As I have learned through my many fieldtrips around Puerto Rico one of the most common fossils in the Cenozoic 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, ~31 million years ago), which was for a while on exhibit in the now defunct 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. Nonetheless it wasn’t the first time that fossil side-necks or other kinds of turtles were found as fossils in Puerto Rico.

Representatives of side-necked turtles; two Podocnemis, possibly, P. unifilis, photo taken in Guayaquil, Ecuador in 2018.

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 around Salto Collazo in the town of San Sebastián (northwestern PR), which means that the fossils came from Oligocene age rocks (Rabell-Cabrero, 1914; MacPhee and Wyss, 1990). Most of the vertebrate material collected by Rabell-Cabrero was later donated to the American Museum of Natural History (MacPhee and Wyss, 1990), while a small portion remained in the Museo de Zoología at UPR-RP (or at least there was when I visited in 2007).

Eventually, some of the specimens collected by Rabell-Cabrero was studied and described by Roger C. Wood and published in 1972. In his paper, Wood describes a shell, plastron and pelvis collected from the San Sebastian Formation (early-late Oligocene age) but due to the incompleteness of the material no species name was given, although similarities with living and extinct South American pelomedusids were noted (Wood, 1972).

Photos from one of my research sites in Puerto Rico, the red circles mark parts of a pelomedusoid turtle shell, the green circle, a sirenian rib. I wrote about this locality here.

Additional fossils of side-necked turtles were discovered in Puerto Rico during the late 1980’s American Museum of Natural History expeditions. These came from early to middle Miocene deposits in northern PR and included a shell, proximal humerus and pubis (MacPhee and 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 and Zangerl, 1968; Wood and Diaz de Gamero, 1971; MacPhee et al. 2003).

Skull of Bairdemys hartsteini, photos from Gaffney and Wood, 2002. 

In the early 2000's a pelomedusoid skull from Puerto Rico was described by Gaffney and Wood (2002). This skull (see photos above) is the type species of Bairdemys harsteini, a new genus that also includes several species from around the Americas, including B. venezuelensis (formerly known as Podocnemis venezuelensis; Wood and Diaz de Gamero, 1971), B. sanchezi, B. winklerae, B. healeyorum, and B. thalassica (Gaffney and Wood, 2002; Gaffney et al. 2008; Weems and Knight, 2013; Ferreira et al., 2015). Bairdemys harsteini was collected from the early-middle Miocene deposits of the Cibao Formation in northern Puerto Rico, in addition to the skull, some shell fragments collected by MacPhee and Wyss (1990) from a nearby locality has 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 species is still unknown), as neurals seem to be present in the shell material assigned to B. harsteini (Wood and Diaz de Gamero, 1971; Gaffney and Wood, 2002; Gaffney et al., 2008). 

Now going back to the Juana Díaz pelomedusoid I mentioned at the beginning. This shell, although missing about the anterior half, does have at least three neural plates, and seems to have been approximately the same size as the material described by Wood (1972), which also has neural plates. Unfortunately, no additional material from the Juana Díaz Formation has been collected recently, so the precise identity of that turtle is still unknown. Other turtle material I have been collecting over the last 15 years primarily comes from the San Sebastian Formation and Lares Limestone (early-late Oligocene age-northern PR). So far all that material seems to be from side-necks and is fairly similar in size and morphology to the Juana Diaz carapace and the San Sebastian form of Wood (1972) (see drawing comparing these with a Cuban shell mentioned below).

A few other fossil side-necks are known from the Greater Antilles, such as Caribemys oxfordiensis from the Jurassic of Cuba, and an unknown pelomedusoid from the early Miocene of Cuba (de la Fuente and Iturralde-Vinent, 2001; MacPhee et al., 2003). Nevertheless, there is still a lot of work, particularly with the fossils from Puerto Rico as I'm pretty sure there is more than one new species waiting to be discovered/described. This particular groups of turtles is nowadays absent in Puerto Rico, at least naturally, so these fossils, like many others, allow us to get a glimpse into the ancient fauna of the island and understand how it has change throughout its geologic history.

References

de la Fuente, M. S., and M. A. Iturralde-Vinent. 2001. A new pleurodiran turtle from the Jagua Formation (Oxfordian) of western Cuba. Journal of Paleontology 75:860-869.

Ferreira, G. S., A. D. Rincón, A. Solórzano, and M. C. Langer. 2015. The last marine pelomedusoids (Testudines: Pleurodira): a new species of Bairdemys and the paleoecology of Stereogenyina. PeerJ 3:e1063.

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.

Gaffney, E. S., and 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, and 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.

MacPhee, R. D. E., M. A. Iturralde-Vinent, and  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.

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

Weems, R. W., and J. L. Knight. 2013. A new species of Bairdemys (Pelomedusoides: Podocnemididae) from the Oligocene (early Chattian) Chandler Bridge Formation of South Carolina, USA, and its paleobiogeofraphic implications for the genus. In: Brinkman, D., P. Holroyd, J. Gardner (eds), Morphology and evolution of turtles, Vertebrate Paleoanthropology series. Netherlands: Dordrecht, 289-303.

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

Wood, R. C., and 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.

Updated: May 23, 2019