The seymouriamorph tetrapod Utegenia shpinari from the ?Upper Carboniferous–Lower Permian of Kazakhstan. Part II: Postcranial anatomy and relationships

Abstract

The postcranial skeleton of the seymouriamorph Utegenia shpinari (?Upper Carboniferous–Lower Permian, Kurgalin Formation, Kazakhstan) is redescribed. Features that distinguish it from other Lower Permian seymouriamorphs (Discosauriscus, Ariekanerpeton, Seymouria) are: broad anterior portion of the interclavicle stem, merging indistinctly into the interclavicle plate; absence of a bulge in the anterior half of such a stem; presence of at least 28 presacral vertebrae; gastralia. The poorly ossified limbs of the largest Utegenia specimens are similar in degree of development to those of larval Discosauriscus, but the almost cylindrical, anterior trunk pleurocentra recall the condition of early juvenile Discosauriscus. A phylogeny of the best known seymouriamorphs, using a small but diverse exemplar from other early tetrapod groups, places Utegenia within seymouriamorphs as sister taxon to discosauriscids (Ariekanerpeton plus Discosauriscus). This conclusion affects origin and dispersal scenarios for seymouriamorphs, and supports the hypothesis of a widespread geographical record of Lower Permian taxa spanning across western Euramerica and eastern Asia.