Xilousuchus sapingensis Wu, 1981

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 : 27

Xilousuchus sapingensis Wu, 1981 ( fig. 8J)

AGE: Late Early Triassic ( Rubidge, 2005).

OCCURRENCE: Heshanggou Formation, Hazhen commune, Fugu County, northeastern Shensi Province, China ( Wu, 1981).

HOLOTYPE: IVPP V 6026, maxillae, premaxilla, lacrimal, nasal, dentary, articular, surangular fragment, splenial, braincase, axis, presacral vertebrae 3–10, primordial sacral two, two distal caudal vertebrae, cervical rib, dorsal rib, clavicle, ungual.

REMARKS: Xilousuchus sapingensis Wu, 1981 , is one of the most completely known archosauriforms from the Early to Middle Triassic of China. Regardless of the exact age of the Heshanggou Formation, Xilousuchus lived along with early archosauriforms such as a Proterosuchus -like taxon and Fugusuchus , a taxon considered to be more closely related to Erythrosuchus than to other archosauriforms ( Gower and Sennikov, 1996).

Xilousuchus was named from a single wellpreserved partial skull and the anterior portion of the presacral vertebral series. As first described, Xilousuchus was referred to the Proterosuchia by Wu (1981), whereas Gower and Sennikov (1996) found it as an erythrosuchian based strictly on the braincase.

Xilousuchus sapingensis differs from all other archosauriforms except Lotosaurus , Ctenosauriscus , and Arizonasaurus in having posterior cervical vertebrae with neural spines that arc anteriorly at the distal end. It differs from Ctenosauriscus in having anteroposteriorly expanded neural spines on the midcervical vertebrae. It differs from Lotosaurus , but not Arizonasaurus , in having a deep pit at the anteroventral margin of the antorbital fossa in the maxilla. Xilousuchus differs from Arizonasaurus in having a deep pit ventral to the descending process of the opisthotic in the parabasisphenoid, the absence of a divided parapophysis of the posterior cervical vertebrae, and poor development of the posterior centrodiapophyseal lamina in the anterior cervical vertebrae.

KEY REFERENCES: Wu, 1981; Gower and Sennikov, 1996.