OSTEOMETRICAL EVOLUTION OF RATTUS-RATTUS AND MUS-MUSCULUS ON SMALL ISLANDS - COMPARISON OF MEDIEVAL AND RECENT POPULATIONS ON THE LAVEZZI ISLANDS (CORSICA) AND CORSICAL MAINLAND

About 2,500 teeth and bones of Rattus rattus and Mus musculus domestic us have been collected in archaeological layers dated from the XIV and XVIIth centuries, on the Lavezzi island (Bonifacio, Corsica). Taphono mical investigations have shown that this material originated mainly f rom barn owl pellets (Tyto alba). Osteometrical comparisons between th ese subfossil remains and recent populations of rats from Lavezzi isla nd and Bonifacio (mainland Corsica) show that jaws and teeth rows were larger in the medieval population, while the two recent populations d isplay only slight differences. Nowadays, the house mouse does not occ ur on Lavezzi island any more. The medieval population has be compared with mice from Bonifacio and with a <<giant>> mouse population from P iana islet (Lavezzi archipelago). The Lavezzi subfossil mice have lowe r teeth rows which are longer than those from Corsican mainland mice a nd similar to those from Piana. Subfossils do not exhibit any other gi gantism feature. The observations suggest a fast evolutionary pattern for both rats and mice. That may result from the interaction between t he release of competition pressures and the duration of isolation, the latter being mostly a consequence of human frequentation.