HISTOLOGICAL COMPARISON OF TEMNOSPONDYL TEETH TO TAXONOMICALLY PLACE NOVEL TEMNOSPONDYL TEETH FROM THE LATE TRIASSIC CHINLE FORMATION AT PETRIFIED FOREST NATIONAL PARK, ARIZONA

Temnospondyls are a clade of anamniote tetrapods that span the Pennsylvanian through the Cretaceous, with stereospondyls being their predominant clade spanning the Mesozoic. Stereospondyls reached their peak in species richness directly after the end-Permian mass extinction. However, this increased species richness was short-lived, and by the Late Triassic, only one clade of large-bodied stereospondyls was present in North America, the metoposaurids. All known metoposaurids are presumed to have occupied the same ecological niche with the exception of one potential diminutive species that may have been slightly more terrestrial. This similarity in niche occupation is likely linked to the congruencies seen in metoposaurid anatomy, especially within the dentitions. Metoposaurid teeth are conical with apico-basally oriented crenulations representing the complex labyrinthine infolding of the dentine (plicidentine). These crenulations extend the entire height of the tooth crown. Moreover, there are two weakly developed carinae on the mesial and distal sides of the tooth, which are restricted to the apical half of the crown. Until recently, this tooth morphology has been the only recognized form of large-bodied temnospondyl tooth from the Late Triassic of southwestern North America.

Here we discuss a novel tooth morphology from the Late Triassic Chinle Formation at Petrified Forest National Park, Arizona. Although the tooth morphology is generally similar to other temnospondyls in possessing plicidentine and carinae, it differs from known Chinle metoposaurids by having deep crenulations restricted to the basal half of the tooth, and strongly pronounced carinae. Although similar teeth have been tentatively assigned to the metoposaurid Koskinonodon, such teeth are isolated from any diagnostic tooth-bearing elements, and their taxonomic affinity has not been verified through more informative methods such as histology. We present histological comparisons of the complexity of the plicidentine infolding of this novel morphology, to known metoposaurid specimens and to the literature representing other families of temnospondyls, to provide a coarse placement of this taxon into a specific temnospondyl clade. These specimens add to the growing diversity of Late Triassic temnospondyls from North America.