Evolutionary lineage of Spermophilus superciliosus – S. fulvus (Rodentia, Sciuridae) in the quaternary of the Dnieper area: An ability of a biostratigraphical implication

Abstract

An extinct ground squirrel species Spermophilus superciliosus was studied with respect to its occlusal morphology, patterns of bunodonty, size and proportions of M3 to clarify spatial and temporal aspects of its interspecific variation and abilities of a biostratigraphical implication of its fossils. This species is well-recognizible and shares with S. fulvus a specific (fulvoid) pattern of the occlusal morphology. At the same time, S. superciliosus demonstrates significant intraspecific variation, which, in general, supports the recognition of previously described subspecies (S. superciliosus palaeodesnensis and S. superciliosus fulvoides). Distinctive features of S. superciliosus palaeodesnensis can be explained by adaptation to feeding on tough, high-abrasive food (grass). This subspecies turns out to be a morphologically well-recognizable and ecologically peculiar representative of the Late Pleistocene fauna of the Northern Dnieper Left Bank area. Previously established morphological differentiation of S. superciliosus fulvoides also finds confirmation in the present study; however, morphological, palaeogeographical and stratigraphical limits of S. s. fulvoides should be clarified. “S. s. fulvoides” may contain three different subspecies to describe.Despite of the significant variability and a long time of existence, definite trends in S. superciliosus evolution are absent, so, neither occurrence frequencies of the studied occlusal characters, nor the patterns of bunodonty can be used as biostratigraphical indices. Instead, subspecies of S. superciliosus turn out to be well-recognizable. These subspecies will be of some biostratigraphical potential, especially after obtaining more detailed picture of intraspecific variation.Spatial distribution of ground squirrel taxa (both species and subspecies) is much more affected by geographical barriers, than those of most of the rodents. It makes the Pleistocene ground squirrels an eminently suitable subject for palaeogeographical reconstructions.