Abstract

Sokatra antitra, n. gen. et sp., is a new side-necked turtle from the Maastrichtian (Upper Cretaceous) Maevarano Formation, Mahajanga Basin, northwestern Madagascar. Sokatra antitra is based on a series of incomplete skulls: a partial skull that lacks the premaxillae and some of the basicranium, a partial skull that has a complete ear region and partial basicranium, and other isolated specimens, including dentaries. Although this species exhibits some features of the North African and Brazilian Euraxemydidae, it does not belong to this family, but instead it is the sister taxon of the magnafamily Podocnemidera of Gaffney et al. (2006, 2011). Characters of Sokatra uniting it with the magnafamily Podocnemidera are: quadratebasisphenoid contact, ventral covering of processus interfenestralis of opisthotic, and at least half of prootic covered ventrally. The laterally open foramen jugulare posterius and the distinct accessory ridge on the maxilla are characteristic, but not unique, features shared with members of the Euraxemydidae. The presence of a small wall posterior to the columellae auris and medial to the incisura columellae auris and the formation of the foramen posterius canalis carotici interni by both the prootic and quadrate are unique to Sokatra. In a PAUP analysis using the character matrix from Gaffney et al. (2006), Sokatra resolves as: (Pelomedusidae, Araripemys (Sokatra (Euraxemydidae (Bothremydidae, Podocnemididae)))). The deep phylogenetic roots of Sokatra indicates the presence of its lineage on Madagascar prior to the beginning of the late Cretaceous.