How Elongated? The Pattern of Elongation of Cervical Centra of Elasmosaurus platyurus with Comments on Cervical Elongation Patterns among Plesiosauromorphs

Abstract

Elasmosaurids comprise some of the most extreme morphotypes of plesiosaurs. Thus, the study of their neck and vertebrae elongation patterns plays a crucial role in understanding the anatomy of elasmosaurids. In this study, the taphonomic distortion of the holotype of Elasmosaurus platyurus and its effects on the vertebral length index (VLI) values are evaluated, and a new index to describe the neck is proposed (MAVLI = mean value of the vertebral elongation index of the anterior two-thirds of neck vertebrae). The results provide a strong foundation for a new scheme of neck elongation patterns that divide the diversity of the neck elongation of plesiosauriomorphs into three categories: not-elongate (MAVLI < 95 and Max VLI < 100), elongate (125 > MAVLI > 95 and 100 < Max VLI < 135), and extremely elongated (MAVLI > 125 and Max VLI > 135).