New Exquisite Ladinian Triassic Nothosaurus youngi From Guizhou, China

A new specimen of Nothosaurus youngi from the Middle Triassic of Guizhou, China

Authors:

Ji et al

Abstract:

The Xingyi Fauna has been known widely for yielding abundant specimens of the pachypleurosaur sauropterygian Keichousaurus hui, the first Triassic marine reptile described from China (Young, 1958). Later stratigraphic studies placed it within the Zhuganpo Member of the Falang Formation (latest Ladinian, Middle Triassic) that is exposed across a wide area ranging from Dingxiao and Wusha (Xingyi, Guizhou Province) to Luoping and Fuyuan (Yunnan Province) (Li and Jin, 2003). Despite the extensive exposure of this unit, K. hui remained the only tetrapod from this fauna until the end of the last century, when limited progress was made in both taxonomic and stratigraphic studies. The situation changed during the last decade when a significant quantity of K. hui material was described in detail, in addition to eight new taxa of Triassic marine reptiles, i.e., Lariosaurus xingyiensis, Nothosaurus youngi, Tanystropheus sp., Yunguisaurus liae, Anshunsaurus wushaensis, Macrocnemus fuyuanensis, Glyphoderma kangi, and Qianxisaurus chajiangensis (Li et al., 2002, 2007; Li and Rieppel, 2004; Cheng et al., 2006, 2012; Rieppel et al., 2006, 2008; Zhao et al., 2008a, 2008b). However, precise stratigraphic and locality information still remained unknown for these new taxa, as well as the Xingyi Fauna at large.

Nothosaurus youngi was named by Li and Rieppel (2004) based on an incomplete skeleton from the Xingyi Fauna. It was characterized by the combination of the following features: pineal foramen located in a trough near the posterior end of the parietal, and the longitudinal diameter of the upper temporal fenestra nearly twice of that of the orbit. The postcranial osteology was only briefly described from the incompletely preserved skeleton, including the vertebrae and ribs, parts of the pelvic girdle, and a forelimb. Most of the pectoral girdle was overlapped by the gastralia, and no information was available for the hind limb.

Here, we describe a new specimen of Nothosaurus youngi that we recovered during an excavation of the fossiliferous levels of the Zhuganpo Member at Nimaigu village in the Wusha Town, Xingyi, Guizhou Province, South China, in 2011. The excavation provided us with precise knowledge of the locality and stratigraphic level of Xingyi Fauna for the first time (see below). The specimen is more complete than the holotype and provides new information on the postcranial osteology of N. youngi, which was not known when the species was erected.