A small podocnemidoid (Pleurodira, Pelomedusoides) from the Late Cretaceous of Brazil, and the innervation and carotid circulation of side-necked turtles

Pleurodires are less specious than cryptodires, together forming the two major lineages of crown-turtles. Their fossil record, however, is rich. A particularly large number of fossil pleurodires, many belonging to Podocnemidoidae, has been recovered from the Late Cretaceous Bauru Group outcrops in south-central Brazil. Here we describe an additional pleurodire from this region, Amabilis uchoensis gen. et sp. nov., based on a partially preserved skull. A. uchoensis is recognized as a Podocnemidoidae by its small entrance to the antrum postoticum and completely developed cavum pterygoidei, being unique among other non-podocnemidid podocnemidoids for its medially open fenestra postotica and absent basioccipital-opisthotic contact. Our cladistic analysis places A. uchoensis as sister-taxon to Hamadachelys + other podocnemidoids. We further explore the neuroanatomy of side-necked turtles with the aid of microcomputed tomography (µCT) of specimens of the main pleurodiran lineages. Our data shed light on the different carotid circulation patterns among pleurodires, and we propose new phylogenetic characters which describe neuroanatomical variation of the group. The optimization of these characters shows two independent acquisitions of a foramen for the palatal branch of the carotid in chelids and podocnemidoids, and a unique loss of the vidian nerve canal in chelids among turtles in general.