Redescription ofCalyptosuchus(Stagonolepis)wellesi(Archosauria: Pseudosuchia: Aetosauria) from the Late Triassic of the Southwestern United States with a discussion of genera in vertebrate paleontology

Abstract

Calyptosuchus wellesiis a medium-sized desmatosuchian aetosaur common in Adamanian (early to middle Norian) age rocks from the Chinle Formation and Dockum Group of the Western United States. Known chiefly from osteoderms, this taxon has never been fully described and non-osteoderm material assigned toCalyptosuchushas been done so based on questionable criteria. Mapping of aetosaurian elements from thePlaceriasQuarry allows for the recognition of associated material providing support for referrals of non-osteoderm material. Furthermore, another previously undescribed specimen from the Chinle Formation of Arizona provides more details about this taxon. PresentlyCalyptosuchuslacks discrete autapomorphies, but can be distinguished from other aetosaurs based on a unique combination of characters supported by a phylogenetic analysis.Calyptosuchusis one of the most common aetosaurians in the Western United States and an index taxon of the early Adamanian biozone. The nameCalyptosuchusis retained and encouraged as the applicable genus name for the specieswellesirather than the often usedStagonolepisbecause assignments of taxa to multi-species genus names are problematic and in this case provides a proposed taxonomic relationship that cannot be unambiguously supported, even by phylogenetic analyses. Because of the inherent limitations of the fossil record, referral of specimens and species to species and genera respectively is an epistemological problem in vertebrate paleontology.