A NEW PISTOSAURID (REPTILIA, SAUROPTERYGIA) FROM THE MIDDLE TRIASSIC OF NEVADA AND ITS IMPLICATIONS FOR THE ORIGIN OF THE PLESIOSAURS

We describe a new pistosaurid sauropterygian, Augustasaurus hagdorni, gen. et sp, nov., from the Middle Triassic of Nevada. The specimen was collected in Muller Canyon. Augusta Mountains, from a late Anisian la minated mudstone unit in the Fossil Hill Member of the Favret Formatio n. Augustasaurus hagdorni is based on a partial articulated skeleton c onsisting of the posterior neck, trunk, shoulder girdle, and both fore limbs. In comparison to Pistosaurus from the Muschelkalk Beds of centr al Europe, the neural spines of the new pistosaurid are lower and long er with autapomorphic saw-cut rugosities and double facets of unfinish ed bone. Augustasaurus hagdorni has reduced front limbs with relativel y short distal elements and a phalangeal formula of 1-1-3-3-1. This co ndition is very different from that in plesiosaurs, the presumed siste r-group of pistosaurids.