The influence of pregnancy on maternal osteology in marine amniotes

Placentotrophy (delivery of nutrients to the fetus throughout pregnancy) is a highly derived reproductive strategy present in most mammals and some other vertebrates, including a handful of reptiles. Even though many different viviparous (life-birthing) reptiles are known in the fossil record, the presence of placentotrophy in these groups has never been documented. This project aims to explore the potential presence of placentotrophy in extinct the viviparous marine reptiles: ichthyosaurs and sauropterygians. Previous work on other animal groups indicates that a change in bone organization, induced by calcium scavening, is likely to be visible if placentotrophy is present. In this study whales are used specifically as comparison for extinct marine reptiles due to their similarity in ecology and bone histology. I will therefore first investigate the effects of pregnancy on bone organization in whales to test whether the patterns seen in terrestrial animals are visible in a fully marine adapted clade. Then, I evaluate if a similar signal is present in extinct marine reptiles. Bone organization will be assessed via bone micro-anatomy, specifically cortical thickness and trabecular bone volume, which have shown to be different in pregnant individuals. Data will be collected using CT scans and drill core samples. This study presents the first attempt to assess the presence of placentrophy in a fossil animal and is a crucial step in understanding the evolution of amniote reproductive strategies. Since many of the necessary clades for understanding this evolutionary puzzle are lost to extinction, utilizing fossil material is essential.