The Pleistocene serpent Wonambi and the early evolution of snakes

The Madtsoiidae were medium sized to gigantic snakes with a fossil record e xtending from the mid-Cretaceous to the Pleistocene, and spanning Europe, A frica, Madagascar, South America and Australia(1-3), This widely distribute d group survived for about 90 million years (70% of known ophidian history) , and potentially provides important insights into the origin and early evo lution of snakes. However, madtsoiids are known mostly from their vertebrae , and their skull morphology and phylogenetic affinities have been enigmati c. Here we report new Australian material of Wonambi, one of the last-survi ving madtsoiids(4-6), that allows the first detailed assessment of madtsoii d cranial anatomy and relationships, Despite its recent age, which could ha ve overlapped with human history in Australia, Wonambi is one of the most p rimitive snakes known-as basal as the Cretaceous forms Pachyrhachis(7) and Dinilysia(8). None of these three primitive snake lineages shows features a ssociated with burrowing, nor do any of the nearest lizard relatives of sna kes (varanoids), These phylogenetic conclusions contradict the widely held 'subterranean' theory of snake origins(9-12), and instead imply that burrow ing snakes (scolecophidians and anilioids) acquired their fossorial adaptat ions after the evolution of the snake body form and jaw apparatus in a larg e aquatic or (surface-active) terrestrial ancestor.