Tuesday, May 19, 2009

Cenozoic Caribbean Crocodylians

Following up* on some neat articles about endemic island crocs over at  Tetrapod Zoology (go here and here). I now bring you what is known so far about the Cenozoic crocodylians of the Caribbean Region.
*or at least trying to!
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).
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 colombianusIkanogavialis gameroiPiscogavialis 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.
The Miocene crocodylians of the Caribbean region are still a mystery. Early Miocene crocodylian remains have been collected in Cuba, Dominican Republic and Puerto Rico (MacPhee & Wyss, 1990; MacPhee et al., 2003; Brochu et al., 2007). The Cuban and Dominican material is still undescribed, hence their affinities are unknown. The fossils from Puerto Rico, consisting of several associated cranial elements (shown below) were collected from the Early Miocene age Cibao Fm (MacPhee & Wyss, 1990; Brochu et al., 2007).  The Cibao fossils consisting of a partial dentary, frontal and partial left squamosal, show a combination of features that excludes it from being a gavialoid, alligatorid, Crocodylus or any other extant taxon (Brochu et al., 2007). This implies that at least during the Early Miocene (and probably even earlier) Puerto Rico, and possibly other islands in the Caribbean as well, where home to an endemic group of crocodylians.
Crocodylian remains from the Early Miocene Cibao Formation of northern Puerto Rico. From Brochu et al., 2007.
Other radiations of island-endemic crocodylians include the extinct Cenozoic Australasian Mekosuchinae and the extant Osteolaeminae, which includes two extinct island endemics: Voay robustus, from Madagascar (Brochu, 2007a; Bickelmann & Klein, 2009) and possibly Aldabrachampsus dilophus, from Aldabra (Brochu, 2006), both from Quaternary deposits.
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.
Berg, D. E. 1969. Charactosuchus kugleri, eine neue Krokodilart aus dem Eozän von Jamaica. Eclogae Geologicae Helvetiae 62:731-735.
Bickelmann, C. & N. Klein. 2009. The late Pleistocene horned crocodile Voay robustus (Grandidier & Vaillant, 1872) from Madagascar in the Museum für Naturkunde Berlin. Fossil Record 12(1):13-21.
Brochu, C. A. 2006. A new miniature horned crocodile from the Quaternary of Aldabra Atoll, Western Indian Ocean. Copeia 2006(2):149-158.
Brochu, C. A. 2007a. Morphology, relationships, and biogeographical significance of an extinct horned crocodile (Crocodylia, Crocodylidae) from the Quaternary of Madagascar. Zoological Journal of the Linnean Society 150:835-863.
Brochu, C. A. 2007b. Systematics and taxonomy of Eocene tomistomine crocodylians from Britain and northern Europe. Palaeontology 50(4):917-928.
Brochu, C. A. & A. D. Rincon. 2004. A gavialoid crocodylian from the Lower Miocene of Venezuela. Special Papers in Palaeontology 71:61-78.
Brochu, C. A., A. M. Nieves-Rivera, J. Vélez-Juarbe, J. D. Daza-Vaca & H. Santos. 2007. Tertiary crocodylians from Puerto Rico: evidence for late Tertiary endemic crocodylians in the West Indies? Geobios 40:51-59.
Domning, D. P. & J. M. Clark. 1993. Jamaican Tertiary marine Vertebrata; pp. 413-415 in R. M. Wright & E. Robinson (eds.), Biostratography of Jamaica. Boulder Colorado, Geological Society of America Memoir 182.
Franz, E. F., G. S. Morgan, N. Albury & S. D. Buckner. 1995. Fossil skeleton of a Cuban crocodile (Crocodylus rhombifer) from a blue hole on Abaco, Bahamas. Caribbean Journal of Science 31:149-152.
Gasparini, Z. 1968. Nuevos restos de Rhamphostomopsis neogaeus (Burm.) Rusconi 1933, (Reptilia, Crocodilia) del “Mesopotamiense” (Plioceno Medio-Superior) de Argentina. Ameghiniana 5:299-311.
Jouve, S., M. Iarochene, B. Bouya and M. Amaghzaz. 2006. New material of Argochampsa krebsi (Crocodylia: Gavialoidea) from the Lower Paleocene of the Uolad Abdoun Basin (Morocco): phylogenetic implications. Geobios 39:817-832.
Jouve, S., N. Bardet, N.-E. Jalil, X. Pereda Suberbiola, B. Bouya & M. Amaghzaz. 2008. The oldest African crocodylian: phylogeny, paleobiogeography, and differential survivorship of marine reptiles through the Cretaceous-Tertiary boundary. Journal of Vertebrate Paleontology 28(2):409-421.
Kraus, R. 1998. The cranium of Piscogavialis jugaliperforatus n. gen., n. sp. (Gavialidae, Crocodylia) from the Miocene of Peru. Paläontologische Zeitchrift 72:389-406.
Langston, W. 1965. Fossil crocodilians from Colombia and the Cenozoic history of the Crocodilia in South America. University of California Publications in Geological Sciences 52:1-152.
Langston, W. & Z. Gasparini. 1997. Crocodilians, Gryposuchus, and the South American gavials; pp.113-154 in R. F. Kay, R. H. Madden, R. L. Cifelli & J. J. Flynn (eds.), Vertebrate Paleontology in the Neotropics: the Miocene fauna of La Venta, Colombia. Smithsonian Institution, Washington, DC.
MacPhee, R. D. E. & A. R. Wyss. 1990. Oligo-Miocene vertebrates from Puerto Rico, with a catalog of localities. American Museum Novitates 2965:1-45.
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.