Abstract
Plesiosaurs are one of the common groups of aquatic reptiles in the Mesozoic, which mainly lived in marine environments. Freshwater plesiosaurs are rare in the world, especially from the Jurassic. The present paper reports the first freshwater plesiosaur, represented by four isolated teeth from the Middle Jurassic fluviolacustrine strata of Qingtujing area, Jinchang City, Gansu Province, Northwest China. These teeth are considered to come from one individual. The comparative analysis of the corresponding relationship between the body and tooth sizes of the known freshwater plesiosaur shows that Jinchang teeth represent a small-sized plesiosaurian. Based on the adaptive radiation of plesiosaurs and the palaeobiogeographical context, we propose a scenario of a river leading to the Meso-Tethys in the Late Middle Jurassic in Jinchang area, which may have provided a channel for the seasonal migration of plesiosaurs.
Highlights
1 Introduction Plesiosaurs are one of the most familiar groups of Mesozoic marine reptiles, which mainly lived in marine environments
All three Chinese genera of freshwater plesiosaurs were attributed to two families of Pliosauroidea; they came from Sichuan (Young 1944; Dong 1980; Gao et al 2004; Peng et al 2005), Chongqing (Zhang 1985) and Yunnan (Xiao et al 1991) in southwestern China and Xinjiang (Young 1973; Wu 1987) in northwestern China
The aforementioned palaeogeographical studies and the work on the evolution of the continental plate movement in China (Hong et al 2005) suggest that there may have been a channel for the seasonal migration of plesiosaurs from Meso-Tethys to freshwater in Jinchang area during the late Middle Jurassic (Fig. 4)
Summary
Plesiosaurs are one of the most familiar groups of Mesozoic marine reptiles, which mainly lived in marine environments. Among the known non-marine plesiosaurs, most are from the fluvial and lacustrine sediments (Andrews 1922; Young 1944; Bartholomai 1966; Young 1973; Dong 1980; Zhang 1985; Wu 1987; Xiao et al 1991; Gao et al 2004; Sato et al 2005; Kear 2006; Sato and Wu 2006; Vajda and Raine 2010; Benson et al 2013; Hornung et al 2013; Vavrek et al 2014) and only a few from limnic–brackish lagoon or estuarine deposits (Wiffen et al 1995; Cruickshank 1997; Cruickshank and Fordyce 2002; Forrest and Oliver 2003; Vandermark et al 2006; Kear 2007; Kear et al 2009; Kear and Barrett 2011; Benson et al 2012; Hampe 2013; Sachs et al 2016; Sachs et al 2017). The megafossil plants, palynoflora from the lower part and the lacustrine invertebrate assemblage from the upper part of the Xinhe Formation (Wu et al 1997; Jiang et al 2003; Lu 2011; Deng et al 2016) indicate that the plesiosaur-bearing horizon is of freshwater origin and late Bathonian in age (Li et al 1982; Du 1985; Zhang et al 2009)
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