The fossil record of snakes: The first 100 million years.

CALDWELL, MICHAEL W.; RANDALL NYDAM; APESTEGUÍA, SEBASTIÁN; GARBEROGLIO, FERNANDO F.; ALESSANDRO PALCI; SIMÕES, TIAGO R.

beijing

Congreso; 8th World Congress of Herpetology. Symposium ?How Lizards Turn into Snakes: Combining Fossils, Phylogeny, Function, Genetics, Development, Morphology & Ecology; 2016

World Society of Herpetology

Fossils of the oldest known snake/stem snake, Eophis underwoodi (Bathonian, Middle Jurassic) cannot represent the point in time of the evolutionary divergence event of the clade Ophidia/Serpentes, as by logic, a fossil of an individual must post-date the origin of the clade of which it is a member. Thus the fossil record of snakes, begins with the first occurrence of E. underwoodi ~167 million years ago, followed by the Upper Jurassic snakes Portugalophis and Diablophis, and the Lower Cretaceous Parviraptor. ?A recent report of a Valanginian-aged snake braincase from South Africa, is tentatively added to this data set.? The earliest snake/stem snake fossil materials suggest that snake morphological disparity and species diversity underwent explosive radiation around a series of unique cranial anatomies. Though the early fossil record is sparse, it illuminates the origins of later Mesozoic snake morphologies from the Cenomanian to the Maastrichtian, that are traditionally considered as characterizing ?snakeness?.From the Cenomanian upward, two broad categories of cranial anatomy characterize these ancient snakes: 1) the ?Macrostomatan? organization; 2) ?Dinilysia-like? organization. The Cenomanian to Maastrichtian distribution of these two classes of cranial organization are also unique: 1) the ?Macrostomatan? assemblages occur in spatially disparate marine environments of the Tethys and globally distributed SupraTethys Seaway; 2) the ?Dinilysia-like? snakes are dispersed, from the Valanginian to the Maastrichtian, on widely separated localities that were once part of the Gondwanan southern continent massif. The transition from a limbed ancestral lizard to a derived stem snake lizard is illuminated by fossils from the first 70 million years, with recent insights highlighting cranial anatomies as a key component of ?snakeness?. New data includes the ?Parviraptor-like? snakes/stem snakes from Upper Jurassic and Lowermost Cretaceous localities in Laurasia, and the newly recognized braincase from the Lowermost Cretaceous of South Africa that shows a ?Dinilysia-like? morphology.