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An adult skeleton of the pistosauroid sauroptery- gian Yunguisaurus liae reveals a number of morphological fea- tures not observed in the holotype, such as the complete morphology of the skull roof, stapes, atlas and axis, ventral view of the postcranium, and nearly complete limbs and tail. Size and morphological differences between the two specimens are mostly regarded as ontogenetic variation, and newly added data did not affect the phylogenetic relationships with other pistosauroids significantly. The number of mesopodia (11 car- pals and 8 tarsals) exceeds that known in any other Triassic marine reptiles and does not serve as a precursor of the plesio- saurian pattern with fewer mesopodia of different topology; it demonstrates variability of the limb morphology among the Triassic pistosauroids. The pectoral girdles of Corosaurus, Augustasaurus and Yunguisaurus may indicate early stages of the adaptation towards the plesiosaurian style of paraxial limb movements with ventroposterior power stroke.

The skull of Augustasaurus hagdorni from the Middle Triassic of northwestern Nevada is described in detail, and compared to those of Pistosaurus and Plesiosaurus. New information amends the earlier description of the postcranial skeleton of Augustasaurus. Phylogenetic analysis corroborates the sister-group relationship of Augustasaurus and Pistosaurus. These two taxa form a clade that is the sister-group of Plesiosaurus. The paleobiogeographical implication of the sister-group relationship of Augustasaurus and Pistosaurus is discussed and linked to the exotic terrane model.

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 laminated mudstone unit in the Fossil Hill Member of the Favret Formation. Augustasaurus hagdorni is based on a partial articulated skeleton consisting of the posterior neck, trunk, shoulder girdle, and both forelimbs. In comparison to Pistosaurus from the Muschelkalk Beds of central Europe, the neural spines of the new pistosaurid are lower and longer with autapomorphic saw-cut rugosities and double facets of unfinished bone. Augustasaurus hagdorni has reduced front limbs with relatively short distal elements and a phalangeal formula of 1-1-3-3-1. This condition is very different from that in plesiosaurs, the presumed sister-group of pistosaurids.