The Vascularization of a Fetal Plesiosaur with Comparisons to Extant Reptiles for Insight

Plesiosaurs, an extinct group of Mesozoic marine reptiles, have long been the subject of multiple studies to understand their unique biology.  While studies using isotopes, comparative anatomy, and histology have brought new understanding about this group, much is still unknown including their movement abilities and ontogeny.  Clarification about plesiosaur movement and ontogeny is obtainable through the study of histology, though it entails destructive sampling of a specimen unless the specimen is scanned and viewed as a 3D image for analysis.  In this study, we present new virtual histological data obtained on a fetal plesiosaur long bone from the upper Maastrichtian Phosphates from Morocco using the synchrotron at the Advanced Light Sources at Lawrence Livermore Labs at Berkeley, California.  The studied material, which represents the second known fetal plesiosaur specimen and the first to be scanned using synchrotron tomography, provides an opportune look to understand the early stages of growth in a plesiosaur long bone.   Four virtual sections were realized along the shaft to calculate bone and vascular area per slice using Avizo and MicroView, providing unique constraints on blood supply in fetal plesiosaurs.  Comparisons with histological thin sections of a polycotilid  neonatal plesiosaur (UNSM 55810) long bone and literature on plesiosaur and extant reptile histology allows for an ontogenetic sequence of a plesiosaur long bone to be constructed.   The ontogenetic sequence constructed in this work provides a groundwork for later biomechanical analyses on the plesiosaur flipper to further understand their movement.