A non-aristonectine plesiosaur from Antarctica reveals new data on the mandibular symphysis of elasmosaurids

Abstract

Elasmosaurids are one of the most abundant fossil marine reptile groups identified from the Upper Cretaceous strata of Antarctica. However, the documented record of intact elasmosaurid skull remains is scarce. In this study, we describe the first non-aristonectine elasmosaurid skeleton from Antarctica that preserves an associated lower jaw. This specimen displays a unique character state combination including three symphyseal alveoli, the angle between the mandibular rami exceeding 90 , and the absence of a ventral symphyseal sulcus or keel. This mandibular configuration has not been observed previously among elasmosaurids, prompting comparisons with other described examples and suggesting that mandibular morphology reached a variability peak during the Maastrichtian, which might be reflective of increased trophic diversity.