Navajosphenodon sani (Simões, Kinney-Broderick and Pierce 2022; MNA.V.12442 formerly MCZ VP 9016, Kayenta Fm, Early Jurassic) was originally considered a sphenodont close to coeval and highly fragmentary Cynosphenodon. In turn, they were considered close to extant Sphenodon. Here this tiny complete subadult specimen nests at the base of the Trilophosaurus + Rhynchosauria clade, taxa omitted from the original study. This clade is derived from the Sphenodontia = Rhynchocephalia. Navajosphenodon further cements this hypothesis of interrelationships. This specimen is about half the size of less complete adult specimens. Due to its tiny size Navajosphenodon is a late-surviving, phylogenetically miniaturized taxon marking the shift from a sphenodontian morphology to a trilophosaur morphology. That radiation occurred earlier, before the Late Triassic.

Trilophosaurus buettneri (Case 1928) Carnian, Late Triassic, ~222 mya, 2.5 m in length, was originally considered a cotylosaur like Diadectes. After the back of the skull became known, Gregory (1945) placed it close to Araeoscelis, who also noted many similarities to rhynchosaurs. Carroll (1988) considered Trilophosaurus a "unique" basal archosaurmorph related to Prolacerta and Proterosuchus. Here, after an analysis based on many more taxa, Trilophosaurus was derived from a sister to Sapheosaurus and Navajoosphenodon and was itself a sister to Azendohsaurus and Mesosuchus, a basal rhynchosaur. The similarities are profound.

Three partial skulls are known for Trilophosaurus, two adults and a smaller specimen widely considered a juvenile. One adult (TMM 31025-207) is represented by an anterior skull. It has a shallow jugal and low naris. The other adult (TMM 31025-140) is represented by a posterior skull with a deep jugal. The juvenile (NMMNH P-4100) also has a deep jugal and preserves an elevated naris. So the two adults likely represent distinct genera and the small one may well be a juvenile.

Distinct from Sapheosaurus, the skull of Trllophosaurus was even more robust with a smaller higher orbit and no lateral temporal fenestra in adults. A new ossification filled the jugal between the two posterior processes. The maxilla ended below the orbit and continued with the similarly toothed palatine after a one tooth gap. The teeth are unique with three lateral cusps. The left posterior skull does not match the right posterior skull. This asymmetry appears to be real.

The cervicals were each longer and taller and decreased cranially. The dorsals had high and long neural spines. The chevrons were robust. The dorsal ribs were gracile.

The scapula was larger as were the forelimbs. The pelvis was ventrally larger. The hind limbs were more robust. Trenchant claws tipped each digit.

Carroll RL 1988. Vertebrate paleontology and evolution. W. H. Freeman, New York.

Case EC 1928. A cotylosaur from the Upper Triassic of western Texas: Journal of Washington Academy of Science 18:177-178.

Dutuit J-M 1972. Découverte d'un Dinosaure ornithischien dans le Trias supérieur de l'Atlas occidental marocain. Comptes Rendus de l'Académie des Sciences à Paris, Série D 275:2841-2844.

Gregory JT 1945. Osteology and relationships of Trilophosaurus: University of Texas, Publication 4401:273-359.

Heckert AB et al. 2006. Revision of the archosauromorph reptile Trilophosaurus, with a description of the first skull of Trilophosaurus jacobsi, from the upper Triassic Chinle Group, West Texas, USA: Palaeontology 4(3):1-20.

von Huene F 1932. Die fossile Reptil-Ordnung Saurischia, ihte Entwicklung und Geschichte. Monographien zur Geologie und Palaeontologie 1(4). 361 p.

Parks P 1969. Cranial anatomy and mastication of the Triassic reptile, Trilophosaurus [M.S. thesis]: University of Texas, 100 pp.

Simões TR, Kinney-Broderick G and Pierce SE 2022. An exceptionally preserved Sphenodon-like sphenodontian reveals deep time conservation of the tuatara skeleton and ontogeny. Communications Biology 5, 195; doi: 10.1038/s42003-022-03144-y

Spielmann JA, Lucas SG, Heckert AB, Rinehart LF, and Richards HR III 2009. Redescription of Spinosuchus caseanus (Archosauromorpha: Trilophosauridae) from the Upper Triassic of North America. Palaeodiversity 2:283-313.

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