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INVESTIGADORES

SCANFERLA Carlos Agustin

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Título:

The first fossil sunbeam snake and the antiquity of modern snake clades

Autor/es:

BHART-ANJAN BHULLAR; GREGORY PAULY; AGUSTÍN SCANFERLA; GABE BEVER

Lugar:

Bristol

Reunión:

Congreso; 69th Annual Meeting Society of Vertebrate Paleontology; 2009

Resumen:

Alethinophidian snakes represent the majority of snakediversity. They include the familiar boas, pythons, and colubrids; and ascattering of lesser-known ?primitive alethinophidians,?among them the pipesnakes and the so-called sunbeam snakes, named for their striking iridescentscalation. Because of the extreme paucity of the snake fossil record, the?primitive alethinophidian? grade has not been uncontroversially recognizedamong extinct snakes, leaving an exceptionally long series of ghost lineagesstretching back at least to the late Mesozoic. These lineages are especiallyimportant because most of the controversy about alethinophidian relationshipsinvolves lack of resolution in early divergences of the clade. We begin to fillthis major gap in the snake fossil record with a new fossil snake from the Eoceneof Texas. Much of the body is preserved, as well as a partial maxilla, theskull roof, and the entire braincase except for the flooring elements.Preservation is exquisite, as evidenced by a complete in situ stapes. CTscanning was used to digitally disarticulate the skull. Several features,including the elongate parietal, the u-shaped frontoparietal suture, themediolaterally expanded braincase, and the very large stapedial footplate,demonstrate the ?primitive alethinophidian? grade of the fossil. Further, adistinctive parietal morphology and aspects of the braincase unambiguouslysupport a close relationship to the New World sunbeam snake, Loxocemus bicolor.The result holds whether a morphological or molecular scaffold approach isused. Thus, the fossil is one of the few fossil crown snakes to be securelyplaceable within snake phylogeny. Moreover, characters of the fossil and Loxocemussupport a suggested affinity of these taxa to the python clade. The presence ofa fossil sister taxon to Loxocemus just north of the distribution of the livingsnake bespeaks the antiquity of the neotropical squamate fauna. It also showsthat the split between pythons and their sister group was ancient and, in conjunctionwith genetic data and information from other fossils, allows an initialestimate of divergence times for the major snake clades.

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