Cranial anatomy of Shuvosaurus inexpectatus, an edentulous poposauroid pseudosuchian from the Late Triassic of Texas

ABSTRACT

Shuvosaurus inexpectatus is an edentulous poposauroid from the late Lacian or earliest Alaunian (Late Triassic) of western Texas, which had been identified primarily from three individuals. A complete repreparation and redescription of the Shuvosaurus cranial elements highlights many of the features that identify it as a poposauroid and a shuvosaurid. Cranial elements unique to Shuvosauridae include an edentulous jaw with a rhamphotheca groove indicating the presence of a beak, a secondary palate formed from the premaxillae and maxillae, and an elongated parabasisphenoid. Shuvosaurus cranial autapomorphies include the articulation of the squamosal and quadratojugal that forms a projection into the posterior edge of the lateral temporal fenestra, the presence of a triangular posterior process of the squamosal, and a basioccipital that is exposed between the exoccipitals, forming the ventral edge of the foramen magnum. In addition to the beak, Shuvosaurus also possessed an extremely large orbit indicating good eyesight, enlarged olfactory bulbs indicating an excellent sense of smell, and enlarged floccular lobes indicating that Shuvosaurus was highly active with good balance and highly developed gaze stabilisation. These cranial adaptations all suggest that Shuvosaurus was not only bipedal but also subsisted on an herbivorous diet.

KEYWORDS:

• Shuvosaurus
• shuvosaurid
• poposauroid
• pseudosuchian
• Triassic
• edentulous

Acknowledgments

The author would like to thank S. Chatterjee for expert guidance and help on this project, A. Gedeon for casting and modelling assistance, R. Hunt-Foster and J. Foster for manuscript preparation assistance, as well as R. Irmis, M. Houle, J. Martz, J. Weinbaum, D. Cunningham, and B. Mueller for discussions and information assistance. Previous drafts of this paper were greatly improved through comments by W. Parker, M. Ezcurra, and an unknown reviewer. The author is also indebted to the Museum of Texas Tech University as well as the late B. Mueller and K. D. Wallace for photography of the specimens and help with the MOTTU related information.

Disclosure statement

No potential conflict of interest was reported by the author(s).