eschweizerbartxxx DOI: 10.1127/0077-7749/2008/0247-0063 0077-7749/08/0247-0063 $ 4.00 ©2008 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart N. Jb. Geol. Paläont. Abh. 2008, vol. 247/1, p. 63 – 78, Stuttgart, January 2008, published online 2008 A choristoderan reptile from the Lower Cretaceous of Transbaikalia, Russia Pavel P. Skutschas, Saint Petersburg With 7 figures SKUTSCHAS, P. P. (2008): A choristoderan reptile from the Lower Cretaceous of Transbaikalia, Russia. – N. Jb. Geol. Paläont. Abh., 247: 63 – 78, Stuttgart. Abstract: New materials of the choristoderan reptile Khurendukhosaurus sp. are described from the Early Cretaceous Murtoi Formation, Transbaikalia. The Transbaikalian species is characterized by fused scapula and coracoid (uncertain polarity character) and such advanced features as a mediolaterally elongated marginal tooth bases, moderately laterally expanded basal tubera on the basioccipital, clavicular facets on the interclavicle that are continuous across the midline, closed vertebral notochordal canals and the absence of the ventromedial crest on dorsal vertebrae. The combination of derived states such as closed vertebral notochordal canals, the presence of small spinous processes below the presacral postzygapophyses, clavicular facets on the interclavicle that are continuous across the midline and the absence of the ventromedial crest on dorsal vertebrae, and primitive states such as closed neurocentral sutures; anteroposteriorly elongated neural spines with transversally expanded and rugose distal tips on dorsal vertebrae, elongated amphi- to platycoelus vertebral centra, and pronounced ventral longitudinal keels on the cervical vertebrae support the attribution of the Transbaikalian choristodere to Khurendukhosaurus. Phylogenetic analysis places Khurendukhosaurus in a one clade with the neochoristoderes, hyphalosaurids, Monjurosuchus and Lazarussuchus. The basal position of Khurendukhosaurus is not confirmed, nor is a referring of Khurendukhosaurus to the neochoristoderan family Simoedosauridae. Key words: Choristodera, Khurendukhosaurus, phylogeny, Early Cretaceous, Asia, Transbaikalia. 1. Introduction The choristoderes are a Laurasian group of extinct aquatic and semi-terrestrial diapsid reptiles known from the Late Triassic to the earliest Miocene (EVANS & HECHT 1993; EVANS & KLEMBARA 2005). Choristoderes are a common element of Late Meso- zoic terrestrial vertebrate assemblages that occupied a spectrum of ecomorphotypes convergent with am- phibious lizards, short-snouted crocodiles, gavials, and even sauropterygians (GAO et al. 2000). In Asia, choristoderes have been found in the Middle Jurassic of Kyrgyzstan (Choristodera indet.), in the Lower Cretaceous of Mongolia (Tchoiria namsarai, T. klauseni, Irenosaurus egloni, Ikecho- saurus magnus, and Khurendukhosaurus orlovi), Russia (Khurendukhosaurus bajkalensis), China (Ike- chosaurus sunailinae, I. gaoi, I. pijiagouensis, Mon- jurosuchus splendens, Philydrosaurus proseilus, and Hyphalosaurus lingyuanensis), and Japan (Shokawa ikoi, Monjurosuchus sp.), and in the Paleocene of Kazakhstan (cf. Simoedosaurus sp.) (SIGOGNEAU- RUSSELL & EFIMOV 1984; BRINKMAN & DONG 1993; EVANS & MANABE 1999; LÜ et al. 1999; EFIMOV & STORRS 2000; LIU 2004; A VERIANOV 2005; GAO & FOX 2005; KSEPKA et al. 2005; MATSUMOTO 2005; A VERIANOV et al. 2006; MATSUMOTO et al. 2007). 517-Skutschas-text 30.01.2008 16:45 Uhr Seite 63