At present, what we know largely derives from fossils collected from two sedimentary deposits, the Juana Diaz Formation and the San Sebastian Formation, found in southern and northern Puerto Rico, respectively. Both deposits represent a range of shallow marine, coastal and riverine deposits which makes them ideal for the preservation of a variety of species ranging across different environments. Since the beginning of last century various works have documented the marine fauna of these formations, from bivalves and gastropods (Hubbard, 1920; Maury, 1920), echinoderms (Jackson, 1922; Gordon, 1963; Velez-Juarbe and Santos, 2008; Donovan et al., 2019), crustaceans (Gordon, 1966; Schweitzer et al., 2006, 2008) and others. Marine vertebrates are present, although scarce, but there are at least three species of dugongids known from these early Oligocene deposits in Puerto Rico, namely "Halitherium" antillense Matthew, 1916, Caribosiren turneri, Reinhart, 1959, and Priscosiren atlantica Velez-Juarbe y Domning, 2014. There is also an interesting fish and elasmobranch fauna that is still largely undescribed. It is within these formations, that we find some of the best evidence for terrestrial plants, semiaquatic (i.e. turtles and crocodylians) and terrestrial vertebrates to whom we dedicate this brief review.
|Representative stratigraphic section of the San Sebastian Formation, showing the location of isotopically-dated units (numbers in bold), and the distribution and occurrence of some of the fossils discussed here. (Modified from Marivaux et al., 2020).|
Some of the earliest Oligocene fossils described from Puerto Rico consisted of a collection of plant remains from the San Sebastian Formation, including leaves, seeds and wood, described by Arthur Hollick (1928) and representing a total of 88 species. This work was followed many years later by the description of the palynoflora by Graham and Jarzen (1969) who reported 40 species, and more recently the description of a fossil seed by Herrera et al. (2014) also from the San Sebastian Fm. Seven species are both represented by leaves/seeds and pollen, so in total these works document a total of 122 plants that were present in Puerto Rico by the early Oligocene (Graham, 1996). Amongst the plants present there are some which are still known to occur naturally in Puerto Rico like Zamia, but others, like Sacoglottis tertiaria, represent a genus that is absent from the Antilles, although it is present in other parts of the Neotropics. This ancient flora also documents the presence of Eugenia which nowadays includes various species of trees and shrubs found in Puerto Rico, including some endemics like Eugenia borinquensis (guayabota de sierra) which is known from the highest elevations in the island. In sum, this collection of fossil plants represents an interesting combination, as it includes taxa that range across a variety of zones (temperate, to warm temperate to mangrove communities) giving us a profile of the flora present in the island from the mountains down to the coast (Graham and Jarzen, 1969; Graham, 1996).
|Examples of fossil plants from the San Sebastian Formation. Top, part of a tree trunk; bottom, a pair of fossil leaves.|
At present there is only one record of amphibians from the Oligocene of Puerto Rico, discovered in the San Sebastian Fm. This was published recently (Blackburn et al., 2020) and not only represents the oldest fossil amphibian from the Antilles, but is also the oldest record in the world of a frog of the genus Eleutherodactylus or coquí as they are commonly called in Puerto Rico and elsewhere. You can read more about this discovery here and here.
|Life reconstruction of the fossil coquí from San Sebastian (aka coquí abuelo).|
TurtlesOne of the group of terrestrial/semiaquatic vertebrates that is found quite frequently in these deposits are turtles. However, so far there is only one publication describing material from the San Sebastian Fm. which belongs to a pelomedusoid or side-necked turtle, a group whose extant species are restricted to freshwater habitats (I wrote about it here; Wood, 1972). Fossils of side-necked turtles are also known from many other Oligocene through Miocene formation in Puerto Rico, including the Juana Diaz Formation. Usually these consist of shell fragments or limb bones, most which have yet to be described in detail. The one exception is a skull from the Cibao Formation (~16-12 million years; Ortega-Ariza et al., 2015) which was dubbed Bairdemys hartsteini Gaffney and Wood, 2002. The skull is well preserved, and represents a genus of turtles that has been since documented to occur in other parts of the Caribbean (Gaffney and Wood, 2002; Gaffney et al., 2008; Ferreira et al., 2015, 2018). So far it seems that pelomedusoids were the dominant group of turtles in the Paleogene and Neogene of the Antilles as no other groups seem to be present. Interestingly, Bairdemys seems to represent an adaptation of pelomedusoids to life in the ocean, differing from their extant relatives, and may have been ecological equivalents to some of the marine turtles that nowadays live in the region (Ferreira et al., 2015).
|Fragmentary remains of a side-necked turtle from the San Sebastian Formation, prior to preparation for further study.|
Crocodiles have been around the Greater Antilles at least since the Eocene (here's an early post on that subject). From the Oligocene the only described species is the gharial Aktiogavialis puertoricensis Velez-Juarbe et al., 2007, from the San Sebastian Fm. The specimen we described consist only of the back end of the skull, but since its discovery, my colleagues and I have collected additional material, including bits of two other skulls and an associated partial skeleton. Part of this material is still getting prepared for subsequent description and publication. A second species of Aktiogavialis was described recently from late Miocene deposits in Venezuela (Salas-Gismondi et al., 2019). This suggest that Aktiogavialis represents a dispersal event from the Greater Antilles into South America.
Additional crocodylian remains are known from the Juana Diaz Formation which seem to seem to represent a different species and not a gharial, but we still need to find more material to be sure. In addition to these Oligocene fossils, in early-middle Miocene deposits in Cuba and Puerto Rico there are remains that seem to represent a group of endemic crocodylians (Brochu et al., 2007; Brochu y Jiménez-Vázquez, 2014). The material is fragmentary, but nevertheless very interesting as endemic groups of crocodylians have been described for other groups of islands around the world, and these from Cuba and Puerto Rico may represent the first example from the Americas.
|Top left, dorsal view of the skull of Aktiogavialis puertoricensis next to a line drawing of the skull of an Indian gharial for comparison.|
Finding fossils of pre-Pleistocene terrestrial mammals is a major challenge in the Greater Antilles as most of the fossiliferous deposits are marine. As such, we must concentrate our efforts in deposits such as those represented in the Juana Diaz and San Sebastian formations. It is still challenging, but we have better chances in those than in the limestone deposits.
The first evidence of Oligocene terrestrial mammals to be documented from the Greater Antilles consisted of the proximal end of a sloth femur (leg bone) discovered in the Juana Diaz Formation and described by Ross MacPhee and Manuel Iturralde-Vinent (1995). This discovery was, in part, what inspired these researchers to look deeply into the geology and paleogeography of the region and its role into the origins of the Greater Antillean land mammal fauna. The discovery of this Juana Diaz sloth suggested that the endemic sloths that inhabited the Greater Antilles until relatively recent times represent an old lineage that colonized the region around 33 million years ago. This eventually led to the proposal of the GAARlandia hypothesis as a potential pathway for colonization of the Greater Antilles by organisms from South America, a subject previously discussed here.
Even though some experts suggest that the affinities of the Juana Diaz sloth need to be carefully revised (Pujos et al., 2017), it has been shown through molecular analyses that Caribbean sloths did indeed arrive to the region a long time ago, and that they represent an endemic group known as Megalocnoidea (Delsuc et al., 2019; Presslee et al., 2019).
|Phylogenetic relationships amongst sloths showing the basal position and divergence time of Caribbean sloths (Megalocnoidea). (From Delsuc et al., 2019:fig. 3.)|
At least two species of caviomorph rodents were present in Puerto Rico during the early Oligocene (Velez-Juarbe et al., 2014; Marivaux et al., 2020). Both species are part of the family Dinomyidae and include Borikenomys praecursor Marivaux et al., 2020, and a second, larger, yet to be named species. As with the sloths and coquí frogs, the discovery of these rodents imply that this particular group colonized the region during the late Eocene-early Oligocene (~33 million years ago) as these are related to species that lived up until about the early occupation of the island by humans. You can read more about their discovery here and here.
|Los dientes de Borikenomys praecursor (izquierda) y del otro roedor fósil (derecha) de la Formación San Sebastian.|
Blackburn, D. C., R. M. Keeffe, M. C. Vallejo-Pareja, and J. Velez-Juarbe. 2020. The earliest record of Caribbean frogs: a fossil coquí from Puerto Rico. Biology Letters 16:20190947.
Brochu, C. A., and O. Jiménez-Vázquez. 2014. Enigmatic crocodyliforms from the early Miocene of Cuba. Journal of Vertebrate Paleontology 34:1094–1101.
Brochu, C. A., A. Nieves-Rivera, J. Vélez-Juarbe, J. D. Daza-Vaca, and H. Santos. 2007. Tertiary crocodylians from Puerto Rico: evidence for late Tertiary endemic crocodylians in the West Indies? Geobios 40:51–59.
Delsuc, F., M. Kuch, G. C. Gibb, E. Karpinski, D. Hackenberger, P. Szpak, J. G. Martínez, J. I. Mead, H. G. McDonald, R. D. E. MacPhee, G. Billet, L. Hautier, and H. N. Poinar. 2019. Ancient mitogenomes reveal the evolutionary history and biogeography of sloths. Current Biology 29:2031–2042.
Donovan, S. K., S. N. Nielsen, J. Velez-Juarbe, and R. W. Portell. 2019. The isicronine crinoid Isselicrinus Rovereto from the Paleogene of the Americas. Swiss Journal of Palaeontology 138:317–324.
Ferreira, G. S., M. Bronzati, M. C. Langer, and J. Sterli. 2018. Phylogeny, biogeography and diversification patterns of side-necked turtles (Testudines: Pleurodira). Royal Society Open Science 5:171773.
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., 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 82:209–229.
Gordon, W. A. 1963. Middle Tertiary echinoids of Puerto Rico. Journal of Paleontology 37(3):628–642.
Gordon, W. A. 1966. Two crab species from the middle Tertiary of Puerto Rico. Transactions of the Third Caribbean Geological Conference, Kingston, Jamaica, 2nd-11th April, 1962:184–186.
Graham, A. 1996. Paleobotany of Puerto Rico - from Arthur Hollick's (1928) scientific survey paper to the present. Annals of the New York Academy of Sciences 776:103–114.
Graham, A., and D. M. Jarzen. 1969. Studies in neotropical botany. I. The Oligocene communities of Puerto Rico. Annals of the Missouri Botanical Garden 56:308–357.
Herrera, F., S. R. Manchester, J. Velez-Juarbe, and C. Jaramillo. 2014. Phytogeographic history of the Humiriaceae (Part 2). International Journal of Plant Sciences 175:828–840.
Hollick, A. 1928. Paleobotany of Porto Rico. New York Academy of Sciences, Scientific Survey of Porto Rico and the Virgin Islands 7(3):177–393.
Hubbard, B. 1920. Tertiary Mollusca from the Lares district, Porto Rico. New York Academy of Sciences, Scientific Survey of Porto Rico and the Virgin Islands 3(2):79–164.
Jackson, R. T. 1922. Fossil echini of the West Indies. Carnegie Institution of Washington Publication 306:1–103.
MacPhee, R. D. E., and M. A. Iturralde-Vinent. 1995. Origin of the Greater Antillean land mammal fauna, 1: new Tertiary fossils from Cuba and Puerto Rico. American Museum Novitates 3141:1–30.
Marivaux, L., J. Velez-Juarbe, G. Merzeraud, F. Pujos, L. W. Viñola Lopez, M. Boivin, H. Santos-Mercado, E. J. Cruz, A. Grajales, J. Padilla, K. I. Velez-Rosado, M. Philippon, J.-L. Léticée, P. Münch, and P.-O. Antoine. 2020. Early Oligocene chinchilloid caviomorphs from Puerto Rico and the initial colonization of the West Indies. Proceedings of the Royal Society B 287:2019806.
Matthew, W. D. 1916. New sirenian from the Tertiary of Porto Rico. Annals of the New York Academy of Sciences 27:23–29.
Maury, C. J. 1920. Tertiary Mollusca from Porto Rico and their zonal relations. New York Academy of Sciences, Scientific Survey of Porto Rico and the Virgin Islands 3(1):1–77.
Ortega-Ariza, D., E. K. Franseen, H. Santos-Mercado, W. R. Ramírez-Martínez, E. E. Core-Suárez. 2015. Strontium isotope stratigraphy for Oligocene-Miocene carbonate systems in Puerto Rico and the Dominican Republic: Implications for Caribbean processes affecting depositional history. Journal of Geology 123:539–560.
Presslee, S., G. J. Slater, F. Pujos, A. M. Forasiepi, R. Fischer, K. Molloy, M. Mackie, J. L. Lanata, J. Southon, R. Feranec, J. Bloch, A. Hajduk, F. M. Martin, R. Salas Gismondi, M. Reguero, C. de Muizon, A. Greenwood, B. T. Chait, K. Penkman, M. Collins, and R. D. E. MacPhee. 2019. Paleoproteomics resolve sloth relationships. Nature Ecology and Evolution 3:1121–1130.
Pujos, F., G. De Iuliis, and C. Cartelle. 2017. A paleogeographic overview of tropical fossil sloths: towards an understanding of the origin of extant suspensory sloths? Journal of Mammalian Evolution 24:19–38.
Reinhart, R. H. 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36:1–146.
Salas-Gismondi, R., J. W. Moreno-Bernal, T. M Scheyer, M. R. Sánchez-Villagra, and C. Jaramillo. 2019. New Miocene Caribbean gavialoids and patterns of longirostry in crocodylians. Journal of Systematic Palaeontology 17:1049–1075.
Schweitzer, C. E., M. A. Iturralde-Vinent, J. L. Hetler, and J. Velez-Juarbe. 2006. Oligocene and Miocene decapods (Thalassinidiea and Brachyura) from the Caribbean. Annals of the Carnegie Museum of Natural History 75(2):111–136.
Schweitzer, C. E., J. Velez-Juarbe, M. Martinez, A. Collmar Hull, R. M. Fledmann, and H. Santos. 2008. New Cretaceous and Cenozoic Decapoda (Crustacea: Thalassinidea, Brachyura) from Puerto Rico, United States Territory. Bulletin of the Mizunami Fossil Museum 34:1–15.
Velez-Juarbe, J., and D. P. Domning. 2014. Fossil Sirenia of the West Atlantic and Caribbean region: X. Priscosiren atlantica, gen. et sp. nov. Journal of Vertebrate Paleontology 34:951–964.
Velez-Juarbe, J., and H. Santos. 2008. Fossil Echinodermata from Puerto Rico; pp. 369–395 in W. I. Ausich and G. D. Webster (eds.), Echinoderm Paleobiology. Indiana University Press, Bloomington, Indiana.
Velez-Juarbe, J., C. A. Brochu, and H. Santos. 2007. A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile. Proceedings of the Royal Society B 274:1245–1254.
Velez-Juarbe, J., T. Martin, R. D. E. MacPhee, and D. Ortega-Ariza. 2014. The earliest Caribbean rodents: Oligocene caviomorphs from Puerto Rico. Journal of Vertebrate Paleontology 34:157–163.
Wood, R. C. 1972. A fossil pelomedusid turtle from Puerto Rico. Breviora 392:1–13.