Plemmyradytes shintoni, gen. et sp. nov., an Early Permian amphibamid (Temnospondyli: Dissorophoidea) from the Eskridge Formation, Nebraska

ABSTRACT

The fossil vertebrate localities near Humboldt, Richardson County, Nebraska, have produced a diverse assemblage of amphibians from near the Permo-Carboniferous (C-P) boundary, including at least one species of dissorophoid (described here), a trimerorhachid, juvenile and adult specimens of the dvinosaur Acroplous vorax, gymnarthrid microsaur material, numerous skeletons, skulls, and isolated vertebrae assignable to two species of the lysorophian Brachydectes, and diadectid teeth. A new genus and species of amphibamid dissorophoid, Plemmyradytes shintoni, is described from the lower half of the Permian-aged Eskridge Formation (early Asselian) near Humboldt. P. shintoni is only the second amphibamid species described from the Permo-Carboniferous midcontinent sequence in the Kansas- Nebraska region. Among amphibamids, it is set apart by the following suite of characters: (1) reduction of the lateral exposure of the palatine, (2) a long, narrow supratemporal (at least twice as long as broad) roofing the otic notch, (3) a posteriorly elongated squamosal, (4) long anterior maxillary teeth, decreasing in size posteriorly, (5) a shallow dentary with a long lateral dentary trough, and (6) dentary teeth that are slightly smaller than the maxillary teeth (approximately one-half to two-thirds as long). A cladistic analysis of 67 dissorophoid characters from 17 taxa supports a clade uniting P. shintoni with ‘Tersomius’ sp. and Micropholis stowi within a monophyletic Amphibamidae. The demonstration of evolutionary trends within the family based on the new data allows a comparison of competing phylogenetic hypotheses.