Abstract

The Early Permian dvinosaur temnospondyl Acroplous vorax Hotton, 1959 is redescribed based on new specimens from the Eskridge Formation of Nebraska, and an unpublished specimen collected from the Speiser Shale of Kansas in 1960, along with reanalysis of previously described Acroplous specimens. The Nebraska Acroplous specimens are part of the oldest Permian (Asselian) nonmarine vertebrate faunal assemblage in the Paleozoic midcontinental sequence of the United States based upon invertebrate biostratigraphy. This study reveals previously unknown anatomi- cal features for Acroplous, requiring a reassessment of the genus and the Eobrachyopidae. Among the new findings for Acroplous are: an anterior dorsal fenestra; prefrontals excluded from the external naris; lacrimal contacting the orbit; denticulated palatine, ectopterygoid and pterygoid; a lack of a postglenoid transverse trough; an unusual interlocking mandibular symphysis, and an elongate rod-like ilium. A cladistic analysis of 87 characters and 12 temnospondyl taxa indicates that the Eobrachyopidae (Acroplous and Isodectes) may be a paraphyletic group, with Isodectes filling a more basal position within the Dvinosauroidea.