A New Rhynchosaur Taxon from the Popo Agie Formation, WY: Implications for a Northern Pangean Early-Late Triassic (Carnian) Fauna

New discoveries in the lower Popo Agie Formation (lower carbonate unit) of central Wyoming necessitated a reevaluation of USNM 494329 from the same unit, the only known hyperodapedontine rhynchosaur in western North America. Well known from Gondwanan deposits, hyperodapedontines appear to be restricted to the Carnian age (Late Triassic), with the exception of Teyumbaita in the earliest Norian age (Late Triassic) of Brazil. Initially assigned to c.f. 'Hyperodapedon' sanjuanensis, our phylogenetic analyses reject this hypothesis, in support of a sister relationship between USNM 494329 (Beesiiwo cooowuse, gen. et. sp. nov.) and Oryctorhynchus bairdi forming an early-diverging clade that is only distantly related to 'H.' sanjuanensis. Five additional specimens recovered from the lower Popo Agie are described. Three are referred to B. cooowuse, and another two are placed closer to Hyperodapedon and the remainder of Hyperodapedontinae. Our analysis demonstrates potential temporal distinction between a grade of earliest-diverging hyperodapedontines (including all Wyoming taxa) and a exclusively Late Carnian, Southern Pangaean hyperodapedontine clade (including 'H.' sanjuanensis). We consider the lower Popo Agie Formation to represent the first nonmarine Late Triassic unit of Western North America that can be confidently restricted to the Carnian age.

Automated summary

New findings in the lower Popo Agie Formation of central Wyoming led to the reevaluation of the only known hyperodapedontine rhynchosaur in western North America. The phylogenetic analysis rejects the previous identification and suggests a close relationship between the USNM 494329 specimen and Oryctorhynchus bairdi. Additional specimens found in the same formation provide further insights into the evolutionary history of the hyperodapedontines. The Popo Agie Formation is considered significant as it represents the first nonmarine Late Triassic unit of Western North America confidently restricted to the Carnian age.