Early Cretaceous choristoderes (Diapsida, Choristodera) from Siberia, Russia

- We provide updated information on the record of Early Cretaceous choristoderes from Siberia (4 geological units, 10 localities).
- We discuss the taxonomic affinities, phylogenetic positions and distribution of the Early Cretaceous Siberian choristoderes.
- We support the idea that a climatic barrier separated the distribution of choristoderes/neosuchians in the Early Cretaceous.
- We analyse the bone microstructure of the Early Cretaceous Siberian choristoderes.

There are ten known Lower Cretaceous localities for skeletal remains of choristoderes in Siberia (Russia). Choristoderan remains at all these localities are represented by isolated bones, usually by isolated vertebrae of Choristodera indet. Three choristoderan taxa in two geological units were identified: the non-neochoristodere Khurendukhosaurus sp. (possibly closely related to the long-necked Sino-Japanese hyphalosaurids) from the Murtoi Formation, Transbaikalia; cf. Khurendukhosaurus sp. and the “Shestakovo choristodere” with possible neochoristoderan affinities from the Ilek Formation, Western Siberia. All these three choristoderan taxa had a microanatomical organization of vertebrae similar to that of in advanced large neochoristoderes (vertebral centra with tight spongiosa). The Siberian fossil record includes the westernmost (Shestakovo locality, Ilek Formation) and the northernmost (Teete locality, the Sangarian Group) occurrences of the Early Cretaceous choristoderes in Asia. Like in other regions of Asia, Siberian localities are characterized by the absence of neosuchian crocodyliforms.