The taxonomic position of the two-horned Rhinoceros from Podpusk-Lebyazhye faunal complex of Western Siberia
Sediments of the Irtysh suite are exposed on the right bank of the River Irtysh in the South-East of the West Siberian plain. The geological age of the sediments corresponds to the Gelasian Age (= Middle Villafranchian). The sands of the Irtysh suite contain the remains of large mammals of the Podpusk-Lebyazhye complex. The species composition of fauna and the evolutionary level of horses and elephants of the mammoth lineage allow us to compare it with Hapry fauna in the South of Eastern Europe (MN 17). The remains of the small two-horned rhinoceros were found among numerous mammal remains in Lebyazhye 2 and Moiseevka 1. The lower jaw fragment with m1 and m2 and metatarsale III are described in this article. The bones are highly mineralized. The teeth are about half worn down. The teeth crowns are slightly tilted forward. The teeth enamel is smooth, shiny, porcelain-like, without any cement. The inner valleys are open, sharply narrowing to the base. They have a triangular shape The depth of the valleys is the same. The valleys are constrained by a low enamel ridge from the lingual side. Metalophid and hypolophid are U-shaped in the cross section. On m1, the width of the metalophid at the crown base is slightly less than the width of the hypolophid. The cingulum is developed on anterior and posterior crown walls of the teeth. The proximal part with a length of 90 mm was preserved from the left metatarsale III. It corresponds to about 2/3 of the bone length. The length of the whole bone could have been about 135 mm. The articular facet with os cuneiforme has a U-shape. There is a well-defined fossa on the medial side. The plantar part of the epiphysis protrudes strongly backwards and overhangs the diaphysis. The antero-posterior and transversal diameters of the proximal epiphysis are close to each other. The diaphysis diameter in the middle part has a wide oval shape with bevelled side edges. The teeth and metatarsale III are small in size (Tables 1 and 2). The comparative analysis of morphometric data showed that the studied remains can be related to Stephanorhinus etruscus Falconer. Its remains are known from Spain to the Caucasus and the Northern Black Sea region. The appearance of the Etruscan rhinoceros corresponds to the end of the Pliocene (MN 16), and its extinction in Eastern Europe occurred in the second half of the early Neo-Pleistocene. On the territories of Kazakhstan and the West Siberian plain, only S. kirchbergensis was reliably known from the genus Stephanorhinus. The remains of S. etruscus from these territories are described for the first time. The meadow-steppe vegetation was developed with the transition to forest-steppe for the time of sediment formation of the Irtysh suite in the South-East of the West Siberian plain. Grasses and meadow grasses, as well as a forest and shrub vegetation, are widely distributed in the spore-pollen spectra. The climate of this time was warm and subhumid. Savanna-type landscapes with watered areas are widely developed. The presence of gazelles, antelopes, camels and horses in Podpusk-Lebyazhye fauna indicates a wide development of open steppe areas and possibly semi-deserts.