Phylogeny and biogeography of fossil and extant Microtus {Terricola) (Mammalia, Rodentia) of Sicily and the southern Italian peninsula based on current dentalmorphological data

摘要

The fossil record of the Savi vole, Microtus (Jerricola) savii, is analyzed in terms of morphological and morphometrical variability of the first lower molar, in order to reconstruct phylogenetic relationships between insular and mainland populations and the dispersal events. The present work gives a contribution to better understand the phylogenetic history of this taxon in Sicily and Southern Italy during the interval Middle Pleistocene - Holocene, in an attempt to reconstruct the relationships between insular and continental voles and to clarify some paleobiogeographical aspects. The morphometrical data have been acquired by traditional measurements of the first lower molar and analyzed by dispersal diagrams and Principal Components Analysis.The fossil Sicilian samples have a greater size variation than extant ones. Two different morphological groups have been identified and named on the basis of the similarity with European or Italian populations: a "subterraneomorph" one (characterized by a tighter symmetric anterior cap and longer anteroconid), similar to European M. (I) subterraneus species, and a "savimorph" one (more confluent and asymmetric anterior cap and shorter anteroconid), occasionally with the accentuation of morphological characters of M. (I) savii.The results, in particular the differences between Pleistocene and Holocene Sicilian populations and the similarities with the mainland ones, suggest that the Savi vole dispersed at least twice in Sicily. One colonization took place likely during the cold stage MIS 6 (recorded at Isolidda 3) with dispersal events, made possible by the sea level drop and the connection with the mainland, and a second one (documented at San Teodoro ave and other Holocene assemblages) during MIS 4 (by dispersal events) or MSS 3 (by accidental transit or limited faunal exchanges).