Gracilisuchus stipanicicorum Romer, 1972c

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 : 19

Gracilisuchus stipanicicorum Romer, 1972c

( fig. 8C–D)

AGE: Ladinian, Middle Triassic ( Rogers et al., 2001).

OCCURRENCE: Chañares Formation, Argentina.

HOLOTYPE: UNLR 08, complete skull, articulated presacral vertebrae and osteoderms, scapula.

REFERRED MATERIAL: MCZ 4116, partially disarticulated skull; MCZ 4117, complete skull; MCZ 4118, partial skull, cervical vertebrae, and osteoderms; PVL 4597, nearly complete skull, presacral vertebrae, osteoderms, sacrum, pelvic girdle, nearly complete hind limb; PVL 4612, nearly complete skull, articulated presacral vertebrae.

REMARKS: Gracilisuchus is known from at least five articulated skulls and much of the postcranial skeleton except for the forelimbs. The forelimb assigned to Gracilisuchus by Romer (1972c) is too small for the size of the holotype, and Sereno and Arcucci (1994b) considered it part of the undiagnostic holotype of ‘‘ Lagosuchus . ’’ Many of the specimens are either dorsoventrally or mediolaterally crushed. As a result, the articulations and orientations of the posterior skull bones have been hotly debated in the literature ( Romer, 1972c; Brinkman, 1981; Parrish, 1993).

Gracilisuchus was first described as an ornithosuchid by Romer (1972c), whereas Brinkman (1981) recognized the completely ‘‘crocodile normal’’ ankle and suggested it was closer to crocodylians. Ever since, Gracilisuchus was found in a variety of positions among crocodylian-line archosaurs. Parrish (1993) found Gracilisuchus as a close relative of Postosuchus and crocodylomorphs, whereas Benton and Clark (1998) found it as a basal suchian. More recently, Benton (2004) found Gracilisuchus as the sister taxon to Phytosauridae . Gracilisuchus has also been used as an outgroup in phylogenetic analyses of basal crocodylomorph relationships (the dataset of Clark et al., 2000). Until recently, Gracilisuchus stood alone as potentially one of the oldest suchians.

KEY REFERENCES: Romer, 1972c; Brinkman, 1981.