New material of the mosasaur Plioplatecarpus nichollsae Cuthbertson et al., 2007, clarifies problematic features of the holotype specimen

ABSTRACT

New material of Plioplatecarpus nichollsae Cuthbertson et al, 2007 (Squamata: Mosasauridae) clarifies many problematic features of the holotype. New observations demonstrate its unique cranial features among plioplate-carpines (=Ectenosaurus, Platecarpus and Plioplatecarpus), such as a parallel-sided frontal shield, a large, oval pineal foramen, and a highly inflated basal tubera of the basioccipital. Although the quadrate morphology is virtually identical to that of Platecarpus ictericus, Plio. nichollsae exhibits more synapomorphies with stratigraphically younger members of the genus than Platecarpus does, including newly recognized characters such as a pair of well-developed parolfactory-bulb recesses and anteriorly diverging ventro-lateral processes found on the frontal. Re-characterization of the species indicates its closest anatomical resemblance to descriptions given for the contemporary Platecarpus somenensis specimens (lower middle Campanian) from North America, which indicates that the current generic assignment for the latter taxon needs to be re-evaluated.