A new trematopid amphibian, Acheloma dunni, is reported based on excellently preserved cranial and postcranial elements recovered from the Lower Permian fissure fill deposits of the Dolese Brothers Co. limestone quarry near Richards Spur, Oklahoma. The new taxon is characterized by distinct lateral exposures of the palatine (l.e.p.) and ectopterygoid (l.e.e.) completely enclosed within the suborbital elements. This large, terrestrial adapted carnivore may represent the top predator of the Richards Spur assemblage. A phylogenetic analysis including 11 ingroup taxa and 54 cranial characters yielded a single most parsimonious tree, placing A. dunni within the monophyletic Trematopidae as the sister taxon to Acheloma cumminsi. Furthermore, the analysis supports including the enigmatic Ecolsonia and Actiobates within Trematopidae, forming a clade with the Upper Pennsylvanian Anconastes and the Lower Permian Tambachia. The study is the first to comprehensively analyze all valid and aberrant forms of Trematopidae within the context of broader dissorophoid phylogeny.

A new trematopid amphibian, Acheloma dunni, is reported based on excellently preserved cranial and postcranial elements recovered from the Lower Permian fissure fill deposits of the Dolese Brothers Co. limestone quarry near Richards Spur, Oklahoma. The new taxon is characterized by distinct lateral exposures of the palatine (l.e.p.) and ectopterygoid (l.e.e.) completely enclosed within the suborbital elements. This large, terrestrial adapted carnivore may represent the top predator of the Richards Spur assemblage. A phylogenetic analysis including 11 ingroup taxa and 54 cranial characters yielded a single most parsimonious tree, placing A. dunni within the monophyletic Trematopidae as the sister taxon to Acheloma cumminsi. Furthermore, the analysis supports including the enigmatic Ecolsonia and Actiobates within Trematopidae, forming a clade with the Upper Pennsylvanian Anconastes and the Lower Permian Tambachia. The study is the first to comprehensively analyze all valid and aberrant forms of Trematopidae within the context of broader dissorophoid phylogeny.