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Date of this Version



HISTORICAL BIOLOGY 2020, VOL. 32, NO. 2, 203–233


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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.