EAPSI: Tracing the Evolution of Sauropterygia toward the Double-Flipper Body Plan of Plesiosauria

Deblois Mark, Davis CA

Investigators

Abstract

Sauropterygia is an extinct group of marine reptiles that evolved a unique body plan characterized by two pairs of wing-shaped flippers for underwater flight. This body plan is fully realized in Plesiosauria, the most successful subgroup within Sauropterygia. Since thrust is produced via oscillations of the limbs in underwater flight, two pairs of flippers would provide more thrust than one. Yet, all other lineages that converged on underwater flight (e.g. penguins, sea turtles, and sea lions) possess only a single pair. Their remaining limbs are distinctly different and serve ancillary functions such as steering in sea turtles. Indeed, the additional set of propulsors may have enabled plesiosaurs to attain much larger body sizes than other underwater flyers. The aim of this project is to ascertain how this body plan arose in Sauropterygia alone. This project will investigate the sequence of transformations in the shape and function of the limbs and body of early sauropterygians leading to plesiosaurs. Since the fossil remains of early sauropterygians most closely related to plesiosaurs are found in China, this project will be conducted in conjunction with Dr. Da-Yong Jiang, an expert in extinct Chinese marine reptiles, at Peking University Geology and Geological Museum. This collaboration will enable access to critical specimens and produce insight into the possible ecological context that underlie sauropterygian evolution. The morphological and concomitant functional transformations toward the plesiosaurian body plan will be investigated via soft tissue reconstruction and direct measurements of the limbs, girdles, and axial skeleton. Comparisons will be made among early sauropterygians (pachypleurosaur-grade taxa and nothosauroids), plesiosaurs, and those that bridge the morphological and phylogenetic gap between them (Wangosaurus and Yunguisaurus). This project is possible because these two newly discovered species from China are superbly preserved and nearly complete. This project will provide insight into sauropterygian paleobiology and convergent evolution across the land-sea transition. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and China?s Ministry of Science and Technology.