Anatomy of the arvicoline radiation (Rodentia): palaeogeographical, palaeoecological history and evolutionary data

Voles and lemmings (Arvicolinae subfamily) diversified throughout the north ern hemisphere over five million years into 140 lineages. Attempts have bee n made to identify relationships within the Arvicolinae on the basis of bio chemical, chromosomal and morphological characteristics as well as on the b asis of palaeontological data. Arvicolines are thought to have originated f rom among the Cricetidae, and the history of voles can be divided into two successive chronological phases occurring in Palaearctic and Nearctic areas . The history of lemmings is not well documented in the fossil record and t heir Early Pleistocene ancestors are still unknown. The arvicoline dispersa l is one of the best known and provides an opportunity to test the anatomy of the radiation and more particularly the punctuated equilibrium model. St udy of arvicolines reveals three modes of evolution: stasis, phenotypic pla sticity and phyletic gradualism. Clearly-the punctuated equilibrium model n eeds to be supplemented by a further component covering disequilibrium in p henotypic plasticity and phyletic gradualism, suggesting a punctuated equil ibrium/disequilibrium model. In terms of palaeogeography, study of arvicoli nes shows that Quaternary climatic fluctuations led to long-range faunal mi grations (3 000 km) and study of these patterns is a significant factor in mapping past environments and climates. Some studies attest to the prevaili ng influence of ecological and ethological factors on skull morphology in a rvicoline rodents sometimes inducing morphological convergences.