Untangling the early evolution of lepidosauria (lizards, snakes, tuatara) using the transitional fossil Megachirella

Lepidosaurs are a diverse group that includes lizards, snakes and the tuatara, making up almost a third of all land vertebrate species today. Their fossil record extends back 245 million years, but the origins and early evolution of lepidosaurs remain obscure. Early fossils are rare, with disputed interpretations, in part due to a lack of good anatomical data for these tiny specimens embedded in rock matrix. We propose to use propagation phase-contrast synchrotron X-ray micro-computed tomography on beamline BM18 to visualise the type and only specimen of the important early species Megachirella wachtleri. Previous lab-based X-ray micro-CT yielded very incomplete and unclear visualization of its anatomy. Synchrotron tomography will provide complete knowledge of the specimen's anatomy, with potential to resolve disagreements about the affinities of Megachirella, and to clarify key uncertainties about the deep evolutionary divergences and anatomical transformations of early lepidosaurs.