EVOLUTION OF THE SIDE-NECKED TURTLES: THE FAMILIES BOTHREMYDIDAE, EURAXEMYDIDAE, AND ARARIPEMYDIDAE

Although pleurodires have been considered significantly less diverse than their sister group, the cryptodires, current discoveries show that pleurodires had a more complex and extensive evolutionary history than had been realized. Previously unknown radiations, particularly in the near-shore marine realm, are revealed by taxa with diverse cranial morphology, indicating many different feeding and sensory strategies. The pleurodire group that is changed the most by the new discoveries is its largest group, the hyperfamily Pelomedusoides. The hyperfamily Pelomedusoides now consists of the families Pelomedusidae, Podocnemididae, Bothremydidae, Araripemydidae, and Euraxemydidae, new family. The families Bothremydidae, Araripemydidae, and Euraxemydidae, new family, are documented with descriptions of skulls, lower jaws, and shells. The relationships of the family Podocnemididae to its sister taxa Hamadachelys and Brasilemys are recognized by placing them in the epifamily Podocnemidinura. The epifamily Podocnemidinura is the sister group to the family Bothremydidae, and together they form the superfamily Podocnemidoidea. The family Araripemydidae consists of one taxon, Araripemys barretoi, from the Aptian-Albian of Brazil. Description of new cranial material suggests that it is the sister group to all other Pelomedusoides or the sister group to the Pelomedusidae, but these relationships are only weakly supported. There is strong support for a multichotomy of Araripemys, Pelomedusidae, and remaining Pelomedusoides. Araripemys is characterized by very thin triturating surfaces and by a shell that lacks mesoplastra and has the first costals reaching the shell margin. The new family Euraxemydidae consists of two new genera: Euraxemys essweini, n. gen. et sp., from the Albian Santana Formation of Brazil, and Dirqadim schaefferi, n. gen. et sp., from the Cenomanian Kem Kem beds of Morocco. Members of the Euraxemydidae are united by the unique possession of a medial process of the quadrate partially covering the prootic and narrowly contacting a ventral process of the exoccipital, in contrast to all other pleurodires, which have either complete exposure or complete covering of the prootic ventrally. Furthermore, members have a ventral process of the exoccipital that is exposed at the lateral margin of the basioccipital in an elongate foot. The Euraxemydidae is hypothesized as the sister group to the superfamily Podocnemidoidea. The family Bothremydidae and the epifamily