Wunyelfia maulensis gen. et sp. nov., a new basal aristonectine (Plesiosauria, Elasmosauridae) from the Upper Cretaceous of central Chile

We describe a near adult, partial postcranial skeleton of an elasmosaurid plesiosaur recovered from upper Maastrichtian beds of central Chile. The specimen includes the atlas-axis, five successive anterior-most cervical vertebrae, several middle cervical centra, cervical neural spines, most of the trunk centra, rib and gastralia fragments, anterior caudal centra and part of the pectoral girdle. Cervical centra have vertebral length indices consistent with adult aristonectines; also, their cervical neural spines are rostrally recurved and constricted in its base, which are features considered diagnostic of the clade Aristonectinae. Available Weddellian aristonectines preserving the atlas-axis were compared with the atlas-axis of the studied specimen. The new morphotype differs in size and sutural arrangements of the atlas-axis with respect to Aristonectes parvidens (upper Maastrichtian of Chubut, Argentina), Aristonectes quiriquinensis (upper Maastrichtian of central Chile) and Alexandronectes zealandiensis (lower Maastrichtian of New Zealand; at least based in its basioccipital condyle versus the atlantal cup of the studied specimen). The studied specimen also possesses anterior cervical vertebrae much different from those of Kaiwhekea katiki (lower Maastrichtian of New Zealand) and Morturneria seymourensis (upper Maastrichtian of Antarctica). Based on these observations, we refer it to a new aristonectine, Wunyelfia maulensis gen. et sp. nov., being the second representative of this clade known to date in the southeastern Pacific during the late Maastrichtian. Phylogenetic analysis recovers this new taxon as a basal aristonectine, consistent with its unique morphology, possessing an atlas-axis with features intermediate between non-aristonectine Weddellian elasmosaurids, and aristonectines.