First record of Seymouria (Vertebrata: Seymouriamorpha) from Early Permian fissure fills at Richards Spur, Oklahoma

Abstract

Isolated skeletal elements of the amphibian genus Seymouria were recently discovered at the Richards Spur locality near Fort Sill, Oklahoma, a prolific source of Early Permian tetrapod remains. Five of the seven described bones are of juvenile size and include three neural arches, a humerus, and a femur, whereas the other two are partial vertebrae, apparently adult. All seven are morphologically similar to equivalent skeletal elements in Seymouria specimens previously collected in Europe and North America, apart from features reflecting the early developmental stage of the juvenile bones. The femur and humerus are clearly distinct from those of other seymouriamorphs such as Ariekanerpeton and Kotlassia. The rarity of Seymouria at the Richards Spur locality implies that it was not a regular component of the fauna, and it is also associated with the less markedly terrestrial assemblage that consistently occurs at localities in the southwestern United States. However, its skeletal morphology and occurrence at terrestrial localities such as Richards Spur imply a primarily terrestrial, rather than an amphibious, mode of life. Conflicting biostratigraphic correlations imply that the exact age of the Richards Spur deposits is uncertain, and equivalence to the Arroyo Formation of Texas may be erroneous.