The second locality of Miocene vertebrate fossils near Baikal was found in Aya Cave on the near-Ol’khon plateau 240 m above the water level. It is confined to alluvial sand-pebble deposits. The alluvium dates from the Middle (Lower-Middle?) Miocene, as inferred from the occurrence of snakehead fish of the family Channidae, tortoises of the genus Trionyx, rodents of the genus Gobicricetodon, and lagomorphs of the genus Amphilagus. The Aya Cave locality is unique owing to the diversity of fossil species. It is for the first time in Siberia that Channidae fishes, Trionyx, Amphilagus, and zapodids have been found. The bone-bearing deposits overlie lacustrine clays and underlie redeposited Middle Pliocene vertisols and Quaternary rocks. The small-mammalian paleofauna is indicative of steppe landscapes, and the rock composition (authigenic carbonates, gypsum, and jarosite) points to the semiarid climate of the Middle (Early-Middle?) Miocene. This is in agreement with the paleoclimatic studies of the Miocene of Ol’khon Island and the Prebaikalian trough performed by N. A. Logachev, V. D. Mats, G. A. Vorob’eva, et al. The remains of Channidae imply that the sedimentation occurred under conditions of a warm (nearly subtropical) climate and anoxic waters rich in aquatic plants. This, however, does not rule out the presence of normally aerated waters, which is confirmed by remains of cyprinids and pikes. For correlation of the Aya paleofauna with the Ol’khon (Tagai) one, the latter should be revised.

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