REVISION OF REDONDASAURUS GREGORII (ARCHOSAURIA: PARASUCHIDAE) FROM THE LATE TRIASSIC (NORIAN-RHAETIAN) OF NEW MEXICO

Redondasaurus gregorii (= R. bermani) is a phytosaur (parasuchid) originally diagnosed based solely on its supratemporal fenestrae being hidden in dorsal view. In contrast, the closely-related Pseudopalatus has slit-like supratemporal fenestrae that are visible in dorsal view. Recognition of this character has varied among phytosaur workers, leading some to consider Redondasaurus synonymous with Pseudopalatus. This has broader significance with the beginning of the Apachean land-vertebrate faunachron (LVF) being defined by the first appearance of Redondasaurus. Historically, study of Redondasaurus has been hampered by the recognition of only four skulls in the literature (three from the Redonda Formation and one from the Travesser Formation). Recent examination of numerous Norian-Rhaetian phytosaur skulls has revealed additional skulls referable to Redondasaurus, bringing the total recognized number of skulls from four to ten. These newly recognized specimens range in size from presumed hatchlings, through juveniles to fully adult individuals and demonstrate sexual dimorphism in the taxon. In addition, previously unrecorded diagnostic characters have been identified that distinguish Redondasaurus from all other phytosaurs, including the closely-related Pseudopalatus. These characters include: a prominent pre-infratemporal shelf at the anteroventral margin of the lateral temporal fenestra; a thickened orbital margin; and an inflated posterior nasal behind the external nares. These features further identify Redondasaurus as a taxon distinct from Pseudopalatus. The presence of Redondasaurus within the Redonda and Travesser formations of east-central New Mexico and the Rock Point Formation of north-central New Mexico demonstrate the utility of the Apachean LVF at the regional level. With the addition of diagnostic characters Redondasaurus may now be recognized from other deposits, allowing the utility of the Apachean LVF to expand globally.