Abstract

The fissure fills of Richards Spur, Oklahoma, together constitute the most productive Paleozoic continental fossil locality in the world, having produced a wealth of terrestrial vertebrates, including occasional articulated skeletons. A new dissorophoid amphibian is represented by two skulls: an exquisitely preserved, complete small skull and the posterior part of a second skull, almost twice the size of the holotype. The specimens provide detailed information about the skull roof, palate, braincase, and mandible, showing that this new taxon is characterized by a relatively elongate skull with large tabulars and postparietals, and monocuspid, recurved teeth that show no sign of pedicelly. The large, laterally expanded interpterygoid vacuities are covered by a mosaic of small dermal plates, each carrying more than a dozen strongly recurved teeth. A phylogenetic analysis of 17 ingroup taxa and 62 cranial and postcranial characters yielded a single most-parsimonious tree with the new taxon in a monophyletic Amphibamidae as the sister taxon to the Lower Triassic Micropholis from South Africa. In addition, the new analysis supports a basal split of Amphibamidae into two distinct clades, one containing the new taxon, Micropholis, along with Tersomius, and the other comprising Amphibamus, Gerobatrachus, Doleserpeton, Platyrhinops, Plemmyradytes, Eoscopus, and Georgenthalia. The data retrieved from this new taxon provides insights into the evolution and diversity of the Amphibamidae.