CONICET | Buscador de Institutos y Recursos Humanos

Thefamily Uropeltidae constitutes a small clade of extant snakes endemic to themoist forests of peninsular India and Sri Lanka. All species of this clade of basalalethinophidian are highly specialized fossorial forms, with extensiveanatomical traits for this mode of life and a singular mode of locomotion. Particularly,the braincase is characterized by fusion of bony elements (except the genus Melanophidium), sizableotic capsules, and a rounded occipital condyle. Up to now, uropeltid snakes have no fossilrecord. Here, we present the first fossil specimen assigned to this clade basedon a small incomplete braincase recently discovered in Late Eocene levels of GesteFormation in the Puna of Catamarca province, Argentina. Contrary with thewidespread condition present in snakes, in the fossil specimen the braincase bonesare fused. As in miniaturized fossorial squamates, the otic capsules areenormous, with a large collumelar footplate closing the fenestra ovalis. Theoccipital condyle is rounded (i.e. fovea dentis absent), a condition onlypresent in uropeltids among squamate reptiles. CT reconstructions allow therecognition of a fenestra pseudorotunda that communicates the vestibular cavitywith the juxtastapedial recess independently to the recessus scalae tympani. Remarkably,this arrangement is only present in uropeltids and the rest of basalalethinophidians commonly labelled as ?anilioids? (Anilius, Cylindrophis, Anomochilus). As in most uropeltids, theforamen for the facial nerve converges with the posterior opening of the Vidiancanal. Taken together, these traits strongly support this systematicallocation. This unforeseen fossil discovery in South America represents abiogeographic challenge due to the restricted Asiatic extant distribution of uropeltidsnakes and the unique paleogeographic history of Indian subcontinent. This newfossil record and the present distribution in a formerly Gondwanan terrainsuggest that the origin of uropeltids occurred in this ancient supercontinent, thusbecoming extant uropeltid species into Gondwanan relicts. Available calibratedtimetrees and relaxed molecular clocks estimate the split between uropeltids andthe rest of alethinophidian snakes 100-80 MA. Given that Gondwanan break-uphappened mostly before this time interval, the presence of an uropeltid in theEocene of South America and the extant distribution of this clade in India musthave explained via transoceanic and/or island-hopping dispersion between WestGondwana (South America and Africa) and East Gondwana (Antarctica, India,Madagascar and Australia). There is a growing body of information that suggestsa bidirectional faunistic and floristic interchange between Africa and SouthAmerica during the Campanian-Eocene time span (80-40 MA) through an island archestablished in the Atlantic Ocean (Rio Grande Rise and Walvis Ridge).Furthermore, a dispersal of several vertebrate taxa with Gondwanan affinitiesto the Indian subcontinent from Africa along the southern margins of theNeotethys around 54 MA ago was proposed recently. In this context, the dispersionbetween India and South America through Africa during a long period between theLate Cretaceous and Paleogene seem to be a plausible biogeographic scenario toexplain the geographic distribution of shield-tailed snakes..