Redondasaurus is an extinct genus of phytosaur from the Late Triassic (221.5 to 201.6 million years ago) of the southwestern United States. It was named by Hunt & Lucas in 1993, and contains two species, R. gregorii and R. bermani. It is the youngest and most evolutionarily-advanced of the phytosaurs. History of discovery The first specimen now described with genus Redondasaurus was found in 1939 by D.E. Savage in the Travesser Formation in New Mexico. Savage originally described this find as Machaeroprosopus. The 1947 discovery of another phytosaur skull in the Redonda Formation, New Mexico, by E.H. Colbert and J.T. Gregory led to the first recognition that both skulls represented a new taxon. In addition, they proposed that the skulls represented the most derived phytosaur in North America due to their supratemporal fenestrae being hidden in dorsal view. A third skull was discovered by D.S. Berman in the 1980s and was later identified as Pseudopalatus (now Machaeroprosopus) buceros. Redondasaurus was first named by A.P. Hunt and S.G. Lucas in "A New Phytosaur (Reptilia: Archosauria) Genus from the Uppermost Triassic of the Western United States and Its Biochronological Significance," published in the New Mexico Museum of Natural History & Science Bulletin in 1993. The authors had previously included the unnamed phytosaur species in a 1992 paper on "Triassic Stratigraphy and Paleontology" in New Mexico. The genus name Redondasaurus is derived from its location of discovery (Mesa Redonda near Tucumcari, New Mexico) and the Greek word "saurus," meaning lizard. Description Redondasaurus, like other phytosaurs, had a very long snout. Known skull lengths range from in juveniles to in very large adults, suggesting total lengths up to . The enamel in the teeth of Redondasaurus has a columnar microstructure. R. gregorii: Differs from other Redondasaurus species in that it lacks a rostral crest. Complete skulls of this species are uncommon, but some fragmentary narrow-snouted phytosaur specimens from the Redonda Formation may be part of the taxon. R. bermani: Differs from other Redondasaurus species in that it has a rostrum with a partial crest. Only one skull of this species has been found, but Hunt and Lucas postulate that "by analogy with other phytosaurs, it is likely that this crested species was sub-equal in abundance with [R. gregorii].". Classification The diagnostic criteria given in 1993 for the new genus was as follows: "Phytosaurid that differs from other genera in possessing supratemporal fenestrae that are