The seymouriamorph tetrapod Utegenia shpinari from the ?Upper Carboniferous–Lower Permian of Kazakhstan. Part I: Cranial anatomy and ontogeny

Abstract

The skull roof, palate and lower jaw of the seymouriamorph Utegenia shpinari (?Upper Carboniferous–Lower Permian; Kurgalin Formation, Kazakhstan) are described in detail, and a new cranial reconstruction is presented. Important features include: skull slightly longer than broad; elongate nasals; deep, elongate posterior cheek region; long, dorsoventrally deep posterior jugal ramus; flat, recurved, blade-like tabular process; denticle-covered anterior ventral part of pterygoid quadrate ramus; transverse pterygoid flange; low radiating ridges with denticle rows on pterygoid and parasphenoid cultriform process; incipient anterior wedge-like process on posterior end of parasphenoid cultriform process; distinct, robust posterolateral processes of posterior plate of parasphenoid. Degree of skull ossification, ornamentation, and absence of ossified quadrate, articular and endocranium suggest that large Utegenia specimens correspond to larval Discosauriscus. In such specimens, dentine infolding extends for almost half of the crown in premaxillary and largest maxillary teeth, as in late larval/metamorphic Discosauriscus. Preliminary results of a regression analysis through some simple skull measurements indicates that, although the preorbital and interorbital regions elongate isometrically relative to the posterior skull table, they do not show a particularly strong linear correlation with the widening of the skull during ontogeny.