Pisanosaurus mertii Casamiquela, 1967

Nesbitt, Sterling J., 2011, The Early Evolution Of Archosaurs: Relationships And The Origin Of Major Clades, Bulletin of the American Museum of Natural History 2011 (352), pp. 1-292 : 49-50

Pisanosaurus mertii Casamiquela, 1967

AGE: Late Carnian–early Norian, Late Triassic ( Rogers et al., 1993, adjusted for the new Triassic timescale of Muttoni et al., 2004).

OCCURRENCE: Middle portion of the Ischigualasto Formation, Ischigualasto basin, Argentina.

HOLOTYPE: PVL 2577, tooth-bearing elements, vertebrae, incomplete hind limb, impression of the pelvis.

REMARKS: Since its discovery, Pisanosaurus was considered the most primitive ornithischian ( Casamiquela, 1967; Bonaparte, 1976; Weishampel and Witmer, 1990; Sereno, 1991b; Irmis et al., 2007a; Butler et al., 2007, 2008b). However, questions about the association of the material plagued certainty regarding the validity of the taxon. Our current understanding of the taxon can be better understood only with the discovery of a new specimen. However, Pisanosaurus is almost always found as the basalmost member of Ornithischia ( Langer and Benton, 2006; Butler et al., 2007, 2008b; Irmis et al., 2007a) because of the combination of ornithischian synapomorphies and archosaur plesiomorphies, such as the anteroventrally directed pubis.

KEY REFERENCES: Casamiquela, 1967; Bonaparte, 1976; Weishampel and Witmer, 1990; Sereno, 1991b; Irmis et al., 2007a; Butler et al., 2008b.