Cerritosaurus – A Key Overlooked Taxon in the Pararchosauriformes

Cerritosaurus binsfeldi,

Figure 1. Cerritosaurus binsfeldi, Late Triassic, known only from a skull. Such a taxon was basal to Chanaresuchus and the chanaresuchids. It also would have been morphologically close to the ancestor of the phytosaurs (parasuchians) and not far from Proterochampsa given its resemblance to the RC 91 specimen of Youngoides.

Where are the Phytosaur and Chanaresuchid Ancestors?
There has been relatively little interest in finding ancestral taxa to the phytosaurs and chanaresuchids. Prior efforts have recovered questionable candidates. Nesbitt’s (2011) tome on archosaurs recovered Euparkeria nesting at the base of the Phytosauria.  He also recovered Vancleavea nesting at the base of the Proterochampsia (= Tropidosuchus + Chanaresuchus). Erythrosuchus nested basal to all the above taxa.

These Nestings Raise Red Flags
Phytosaurs and chanaresuchids were flat-headed archosauriformes with skulls wider than tall and nares located dorsally on the skull. The orbits were located high on the skull. The rostrum was narrow in dorsal view and the “cheeks” flared widely. The antorbital fenestra was small. By contrast the skulls of VancleaveaEuparkeria and Erythrosuchus were taller than wide, with narrow cheeks, lateral nares and the latter two had a large antorbital fenestra. Vancleavea did not have an antorbital, mandibular or upper temporal fenestra because indeed it was not related to archosaurs. Vancleavea was a thalattosaur as reported earlier. Nesbitt (2011) did not include other thalattosaurs in his analysis, so Vancleavea nested by default within the Archosauriformes. The large reptile study solves that shortcoming.

Cerritosaurus binsfeldi (Price 1946, Fig. 1) Late Triassic, ~210 mya, nests here between the Parasuchia and the base of the Chanaresuchidae within the Pararchosauriformes. Nesbitt (2011) briefly mentioned Cerritosaurus as a member of the Proterochampsia [a paraphyletic taxon]. With its short snout and generally primitive characters Cerritosaurus likely also resembled the common ancestor of the Choristodera, Parasuchia and Proterochampsa. It was also not far from the RC 91 specimen of Youngoides (Fig. 1).

Distinct from RC91Cerritosaurus had a skull with a downturned rostrum. The skull was box-like with distinct rims both anterior and posterior to the orbits. The nares opened dorsally. An antorbital fenestra appeared with a deep fossa. The dorsal squamosal flared posteriorly. The mandibular fenestra was enlarged. The retroarticular process ascended. The teeth were extremely long, which is an autapomorphy.

With its wide flat skull, dorsal nares and elevated orbits Cerritosaurus provides a nearly ideal transitional taxon linking the RC91 specimen of Youngoides to basal phytosaurs and chanaresuchids. It is certainly a superior candidate compared to the taller narrow skulls of Euparkeria and Erythrosuchus. Exclusion of Cerritosaurus by Nesbitt (2011) and others before him impaired those earlier studies.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Bonaparte JF 1971Cerritosaurus binsfeldi Price, tipo de uma nova família de tecodontes (Pseudosuchia-Proterochampsia). Anais da Academia Brasileira de Ciências, 43(Supl.): 417-422.
Kischlat E-E and Schultz CL 1999. Phylogenetic analysis of Proterochampsia (Thecodontia: Archosauriformes): Ameghiniana, v. 36, p. 13R.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Price LI 1946. Sôbre um novo pseudosuquio do Triássico superior do Rio Grande do Sul: Boletim da Divisão de Geologia e Paleontologia, DNPM, v. 120, p. 7-38.

wiki/Cerritosaurus

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