A Choristoderan Reptile from the Lower Cretaceous of Transbaikalia, Russia

517-Skutschas-text 30.01.2008 16:45 Uhr Seite 63

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 namsarai, T. klauseni, Irenosaurus egloni, Ikecho- saurus magnus, and Khurendukhosaurus orlovi), The choristoderes are a Laurasian group of extinct Russia (Khurendukhosaurus bajkalensis), China (Ike- aquatic and semi-terrestrial diapsid reptiles known chosaurus sunailinae, I. gaoi, I. pijiagouensis, Mon- from the Late Triassic to the earliest Miocene jurosuchus splendens, Philydrosaurus proseilus, and (EVANS & HECHT 1993; EVANS & KLEMBARA 2005). Hyphalosaurus lingyuanensis), and Japan (Shokawa Choristoderes are a common element of Late Meso- ikoi, Monjurosuchus sp.), and in the Paleocene of zoic terrestrial vertebrate assemblages that occupied Kazakhstan (cf. Simoedosaurus sp.) (SIGOGNEAU- a spectrum of ecomorphotypes convergent with am- RUSSELL & EFIMOV 1984; BRINKMAN & DONG 1993; phibious lizards, short-snouted crocodiles, gavials, EVANS & MANABE 1999; LÜ et al. 1999; EFIMOV and even sauropterygians (GAO et al. 2000). & STORRS 2000; LIU 2004; AVERIANOV 2005; GAO In Asia, choristoderes have been found in the & FOX 2005; KSEPKA et al. 2005; MATSUMOTO Middle Jurassic of Kyrgyzstan (Choristodera indet.), 2005; AVERIANOV et al. 2006; MATSUMOTO et al. in the Lower Cretaceous of Mongolia (Tchoiria 2007).