Similarities and differences in the ilia of Late Cretaceous anurans and urodeles

Abstract

AbstractScreen-washing of matrix from 37 Upper Cretaceous microvertebrate localities in southern Utah, USA, yielded a rich sample of anuran disarticulated bones, including nearly 200 ilia. Because the bones are relatively small and delicate and were subject to pre-mortem transport and unavoidable damage when the fossiliferous matrix was collected and processed, none of the recovered ilia retained intact shafts. This means that features such as the form of the anterior end of the shaft and the presence and form of a dorsal crest cannot be used to identify the fossils. Urodele bones also are known from many of the same localities. When anuran and urodele ilia are isolated and missing much of their shafts, they are superficially similar, so it was important to reliably differentiate ilia of the two groups. Here we provide a list and brief descriptions of some of the features that we found useful for distinguishing between anuran and urodele ilia. These features relate to differences between the two groups in muscle attachments, contacts between pelvic bones, and structure of the acetabula. Because all of the features exhibit some variation, we recommend that they be used in combination when trying to distinguish between anuran and urodele ilia.