Anatomical study of two previously undescribed specimens of Clevosaurus hudsoni (Lepidosauria: Rhynchocephalia) from Cromhall Quarry, UK, aided by computed tomography, yields additional information on the skeleton and hitherto undescribed bones

We investigate two well-preserved and previously undescribed specimens of Clevosaurus hudsoni from a Late Triassic fissure deposit at Cromhall Quarry, SW Britain. For the first time computed tomography (CT) scans of British Triassic fissure specimens have been successfully digitally segmented. Visualisation software was used to isolate bone from matrix and to separate individual bones from each other, revealing hidden cranial and postcranial elements. The CT data, together with stereoscopic microscope analysis, have enabled a full evaluation of the specimens including previously poorly known or undescribed elements of the type species of the clevosaur clade. We present detailed descriptions of the cervical vertebrae including the atlas-axis complex. Little studied bones such as the gastralia and epipodials are detailed here and a gap in the lower temporal bar is confirmed. Sclerotic ossicles are presented for the first time for C. hudsoni. A fully fused scapulocoracoid and unfused astragalus and calcaneum provide new insights into clevosaur ontogeny. The CT scans provide key information on post mortem movement and taphonomy of the specimen, revealing fragmentation of part of the skull by the right arm, which has been thrust into the right side of the skull displacing both cranial and jaw bones.