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.|
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.|
|Skull of Bairdemys hartsteini, photos from Gaffney and Wood, 2002.|
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.
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.
Updated: May 23, 2019
This is really interesting, Jorge, thanks for sharing it. I wonder, are cryptodires also known from these rocks?
Hi Brian, thanks!! No cryptodires known so far from these rocks. However, there are some Pleistocene records of Geochelone, such as Geochelone monensis from nearby Mona Island (Williams, 1952) as well as Trachemys cf. decussata from northern PR (Pregill, 1981). According to Hedges (2006) the origin of Trachemys extends back to the Late Oligocene. But, this is based on molecular data and Oligocene or Miocene fossils belonging to this genus have not been found yet anywhere in the Antilles to support this estimate. So maybe they were there and the fossils are still out there waiting to be found, or these arrived more recently to the region.
Hedges, S. B. 2006. Paleogeography of the Antilles and origin of West Indian terrestrial vertebrates. Annals of the Missouri Botanical Garden 93:231-244.
Pregill, G. K. 1981. Late Pleistocene herpetofaunas from Puerto Rico. Miscellaneous Publications University of Kansas Museum of Natural History 71:1-72.
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 99:541-560.
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