Expansion, speciation and a change of trophic niche: a case study of the Early Pleistocene ground squirrels Spermophilus polonicus and S. praecox

During the Early Pleistocene, two ground squirrel species, Spermophilus praecox (northern Black Sea area) and S. polonicus (Central Europe) coexisted in geographically well-separated ranges. Studied samples from Tiligul (Ukraine) and Kamyk (Poland) have approximately the same biostratigraphical age: the early Odessa faunal complex (Tiligul) and the Villanyian-Biharian transition (Kamyk). A significant difference in trophic niches and a high...