Late Pleistocene and Holocene small mammal faunas from the South Trans-Urals

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Bone remains of rodents and small lagomorphs (c. 24,000 cheek teeth) extracted from unconsolidated sediments of five karst cavities of the South Trans-Urals have been examined. On the basis of 14C dates, two of these sites, the Syrtinsky and Alexeevsky caves, are regarded as key localities for the region; thus the main conclusions regarding the regional fauna composition and structures have been based on the fossil assemblages from these two sites. The species richness of rodent communities was calculated; the number of species changed over time. The total number of species found in the sequences amounted to 21; 15 of which occurred in both Late Pleistocene and Holocene assemblages. Four species appeared only in the beginning of the Holocene; the yellow steppe lemming and small jerboa ( Pygeretmus) were noted to disappear at the end of the Sub-Boreal and do not occur in the modern fauna of the region. In the Late Pleistocene communities, Lagurus lagurus, Eolagurus luteus and Microtus gregalis were dominant. In the Holocene faunas, the narrow-skulled vole began to dominate and the steppe lemming decreased significantly in numbers, while the percentage of the common vole ( Microtus arvalis) increased, though this species can be regarded as an azonal element in steppe associations. The proportions of xerophilic and mesophilic rodent species changed significantly during the interval examined: from 90% and 2% in Late Pleistocene communities to 30% and 35%, respectively, by the end of the Holocene.