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| Sonselasuchus cedrus Smith & Sidor, 2026 Artwork by Gabriel Ugueto |
ABSTRACT
Shuvosauridae is a clade of pseudosuchian archosaurs currently represented by three named species characterized by a body plan strikingly convergent with that of ornithomimid theropod dinosaurs. This paper documents a new genus and species of shuvosaurid from the Upper Triassic Chinle Formation of Petrified Forest National Park, Arizona. Sonselasuchus cedrus, gen. et sp. nov., is largely diagnosed by features of the maxilla, including a reduced body and anterior process, an enlarged subnarial foramen, and an expanded facet on the posterior process, although other unique cranial features are also noted herein. By contrast, its postcranial anatomy is largely similar to what has been described for other shuvosaurids, although subtle differences are noted. A phylogenetic analysis finds S. cedrus in an unresolved clade with Effigia okeeffeae and Shuvosaurus inexpectatus, likely as a result of non-overlapping missing data, particularly for the skull of Shuvosaurus. A review of the shuvosaurid fossil record indicates that shuvosaurids were persistent components of Late Triassic terrestrial vertebrate faunas in North America. S. cedrus is represented by a minimum number of 36 individuals, mostly skeletally immature, that occur within a multitaxic bonebed of almost exclusively disarticulated elements. An analysis of the relative size change of limb dimensions indicates the forelimb was growing on a negative allometric trajectory relative to the hindlimb, which is consistent with a transition in locomotory mode from quadrupedal to bipedal in S. cedrus during ontogeny.
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| Life restoration of Sonselasuchus cedrus as depicted by Gabriel Ugueto. Note the occurrence of individuals in both bipedal and quadrupedal stances. |
SYSTEMATIC PALEONTOLOGY
ARCHOSAURIA Cope, Citation1869
PSEUDOSUCHIA Zittel, Citation1887–Citation1890
PARACROCODYLOMORPHA Parrish, Citation1993
POPOSAUROIDEA Nopcsa, Citation1923
SHUVOSAURIDAE Chatterjee, Citation1993
SONSELASUCHUS CEDRUS gen. et sp. nov.
Etymology—For the genus, ‘Sonsela’ refers to the Sonsela Member of the Chinle Formation, the type section is located at the Sonsela Buttes on the Navajo Nation; ‘suchus’ is a Latinization of the Greek word soukhos, for the Egyptian crocodile deity Sobek, reflecting the pseudosuchian affinities of the taxon. The specific epithet, ‘cedrus’ is the genus name for the common cedar (actually the juniper, Juniperus spp.) and refers to Cedar Tank, the geographic feature in Petrified Forest National Park near the type locality.
Holotype—PEFO 47305/UWBM 119436, left maxilla.
Locality and Horizon—The Kaye Quarry (PFV 410/UWBM C2226) is located west of Cedar Tank at Petrified Forest National Park, Apache County, Arizona, U.S.A. (Fig. 1). The site is within the Jim Camp Wash beds of the Sonsela Member of the Chinle Formation and is Norian in age (Marsh et al., 2024). ...
Elliott Armour Smith and Christian A. Sidor. 2026. Osteology and Relationships of A New shuvosaurid (Pseudosuchia, Poposauroidea) from the Upper Triassic Chinle Formation of Petrified Forest National Park, Arizona, U.S.A. Journal of Vertebrate Paleontology. e2604859. DOI: doi.org/10.1080/02724634.2025.2604859 [08 Mar 2026]
