THE PHYTOSAUR NICROSAURUS BUCEROS IN THE UPPER TRIASSIC OF THE CHAMA BASIN, NORTH-CENTRAL NEW MEXICO

The first North American phytosaur taxon known from a skull was Belodon buceros Cope, 1881, from the Chinle Group of the Chama basin, north-central New Mexico. This species has been referred to several genera, including Nicrosaurus, Pseudopalatus, Phytosaurus, Machaeroprosopus and Arribasuchus. The type skull displays diagnostic features of Nicrosaurus, including a moderately wide postorbital-squamosal bar and supratemporal fenestra short and narrow in dorsal view. However, it differs from Nicrosaurus kapffi (von Meyer) in that it possesses a relatively narrow (altirostral) snout, so we refer to Cope's species as Nicrosaurus buceros. Recent archival research indicates that the type specimen comes from the type locality of the aetosaur Typothorax coccinarum Cope in the Painted Desert Member of the Petrified Forest Formation at Cerro Blanco, near Gallina. Typothorax coccinarum is an index taxon of the Revueltian (early-middle Norian) land vertebrate faunachron, and Nicrosaurus buceros also occurs in Revueltian-age localities in the Painted Desert Member elsewhere in the Chama basin (Canjilon and Snyder quarries near Ghost Ranch). The co-occurrence of Nicrosaurus in the Painted Desert Member and in the German Stubensandstein, which is Norian in age, supports a Revueltian-Norian correlation and strengthens existing correlations of the Chinle with the German Keuper.