Paleogene Squamates from the Northern neotropics: Ecological Implications and Biogeographic Histories. (original) (raw)

72nd Annual Meeting of the Society of vertebrate Paleontology. Program and Abstracts, 2012:108. The modern northern Neotropics possesses some of the highest diversity among extant squamates, but the sparse fossil record from this region has previously limited the ability to reconstruct their evolutionary histories. New discoveries from the early Paleogene of northern South America reveal biogeographic patterns and paleoecology of modern clades. Squamates have been recovered as components of vertebrate faunas from the late Paleocene Cerrejón Formation and late Paleocene- early Eocene Bogotá Formation of Colombia. The Cerrejón Formation represents large-scale fluvial deposits with associated rainforest flora and herpetofauna. The squamate record consists of snakes, including multiple individuals of the giant aquatic boid Titanoboa cerrejonensis and a single, poorly preserved precloacal vertebra assigned to Anilioidea on the basis of extreme reduction of the neural spine, broadly concave dorsal margin of the neural arch and comparatively narrow zygosphene. The presence of a fossorial to leaf-litter specialist provides the first the first terrestrial component to the reptile record and indicates geographic proximity of the aquatic record to rainforest habitats within the Cerrejón Formation. The Muchelo Creek locality in the Bogotá Formation is dated to just before the Early Eocene Climatic Optimum (EECO). It represents smaller scale fluvial deposition, and preserves a diverse squamate fauna consisting of iguanians, including the fossil record of hoplocercines, and boine, caenophidian, and ungaliophiine snakes. Modern members of these clades include arboreal taxa, and the Bogotá squamate record represents a forest herpetofauna. Extant tropical forest squamates undergo thermal stress at high ambient temperatures, and inferred thermal tolerances of the Bogotá squamate record may constrain temperature estimates at the beginning of the equatorial EECO. The Colombian squamate record indicates that the continental-scale biogeographic zonation of the modern northern Neotropics was established no later than the middle Eocene. Both the Bogotá and Cerrejón formations include representatives of extant clades that are either endemic or predominately South America (“anilioids”) or whose Central American distributions are limited or represent more recent immigration from South America (hoplocercines, boines). These records additionally indicate that the biogeographic events that initially assembled Neotropical squamate faunas, including New World immigration of iguanians and first occurrence of South American boines, were likely late Mesozoic in age.