Morphological and histological description of small metoposaurids from Petrified Forest National Park, AZ, USA and the taxonomy of Apachesaurus

Authors

Bryan M. Gee, University of Toronto Mississauga & Petrified Forest National ParkFollow
William G. Parker, Petrified Forest National Park

ORCID IDs

http://orcid.org/0000-0003-4517-3290

http://orcid.org/0000-0002-6005-7098

Date of this Version

5-22-2018

Citation

HISTORICAL BIOLOGY 2020, VOL. 32, NO. 2, 203–233 https://doi.org/10.1080/08912963.2018.1480616

Comments

U.S. Government Works are not subject to copyright.

Abstract

Metoposaurids are Late Triassic temnospondyls that are abundant components of freshwater deposi- tional settings. Although metoposaurids are represented by hundreds of specimens in collections around the world, the vast majority pertain to large-bodied, relatively mature individuals, and as a result, the early stages of ontogeny are still poorly characterised. Small-bodied metoposaurids from North America have traditionally been assigned to Apachesaurus gregorii, interpreted as a diminutive taxon, but this interpretation has not been rigorously tested. Here we provide a morphological description of two new small-bodied metoposaurid specimens from Petrified Forest National Park, AZ, USA. Both provide various anatomical details that improve our understanding of small-bodied metoposaurids and their taxonomic placement within Metoposauridae. Furthermore, we perform a histological analysis on associated intercentra of these specimens, which indicates that these are relatively immature individuals. These findings support the growing consensus that Apachesaurus is a juvenile metoposaurid, thereby providing additional data regarding the early stages of metoposaurid ontogeny and evidence of the persistence of large-bodied forms into the late Norian. Accordingly, these findings merit a reevaluation of the taxonomic validity and diagnosis of the taxon and of the previous interpretations of its paleobiology.