Fossil Sponge Fauna in Lake Baikal Region

Abstract

The spicules of almost all the known recent sponges that nowadays inhabit Lake Baikal have been found in the sediments of the Late Pliocene (3.2 Ma). However, the sponge fauna in Late Pliocene (3.2-2.8 Ma) was richer by far than the recent one. Besides the spicules of nearly all the recent sponges, 24 types of spi cules belonging to "extinct species," which have no analogues with recent sponges, have been found.The species' composition of the sponge fauna in the Late Pleistocene period (95 Ky) was similar to the recent one.In the sediments of the Late Miocene (6.50-4.75 and 10 Ma), the well-formed spicules of species of the Lubomirskiidae family can be found. To these belong: Rezinkovia arbuscula Efremova, 2001, Baikalospongia fungiformis (Makuschok, 1927), Swartschewskia papyracea (Dybowski, 1880) and Lubomirskia incrus tans Efremova, 2001. We can also find here four types of spicules in the genus Lubomirskia which have no analogues with the recent sponges. A few types of spi cules in the Spongillidae family are also "new." According to our preliminary brief investigation of the species' composition in the sediment of this period (6.50-4.75 and 10 Ma), the sponge fauna of the Late Miocene is poorer compared to the sponge fauna in Late Pliocene. In the sediments of the Late Miocene (6.50-4.75 Ma) in cold climactic periods, spicules of the family Lubomirskiidae predominate while in warm periods the Spongillidae spicules dominate. Thus, a permanent change in the sponge association took place.