Vertebrate Evolution and Extinction on Western and Central Mediterranean Islands.

Abstract

The Mediterranean region, like other biogeographic regions located between continental plates, is rich in islands. Most of them are oceanic-like islands, Le., islands that have been previously connected to the surrounding continents and are faunistically similar, but not identical, to oceanic island (because the island-continent connections occurred in a distant past, were of a short duration, and/or promoted a highly selective and limited faunal transfer). Insular (Le., non-continental) vertebrate faunas are known in several Mediterranean islands from the Lower Miocene to Recent times. This paper presents an overview of these faunas in the Western and Central Mediterranean. I will emphasize the following points: 1. Island's geological succession in the western Mediterranean area. 2. Faunistic successions occurring on the different islands. 3. Global analysis of the Mediterranean insular faunas. 4. Record and analysis of some extreme cases of insular evolution. 5. Extinction of the Mediterranean insular faunas. The Mediterranean region has changed substantially from Eocene to current times. A record of the transformation of Mediterranean islands during geological time is presented in this paper. Some territories that were islands in the past (e.g., Gargano, Scontrone, Baccinello, Las Murchas) have been integrated into the mainland and are now continental areas displaying insular fossil faunas. They are considered "fossil islands". Merging of islands have also occurred (e.g., Mallorca, Sardinia, Crete) as well as some island splitting (e.g., Gymnesic islands). In Sardinia, Mallorca, Menorca and Eivissa, there is a long fossil record documenting several faunistic successions. There, the faunistic turnover affected different taxonomic groups in different ways. Mammals were specially prone to extinction after new invasions. The fossil insular vertebrate faunas from Mediterranean islands are peculiar. They differ both from typical oceanic insular faunas (usually devoid of mammals and amphibians) and the typical continental faunas (lacking endemic species). They are characterized by three main traits: (1) absence of mammal predators, (2) presence of terrestrial mammals and in some cases amphibians, and (3) high rates of endemic species, including some very bizarre taxa. Even though there are some exceptions, it is possible to define several global faunistic patterns for Mediterranean insular faunas. Evolutionary changes in insular Mediterranean vertebrates have usually been small (Le., alterations in body size and proportions that do not change substantially the life style of the species). Nevertheless, in some cases insular evolution produced very big changes (changes not only in body size and proportions, but also in assemblages of structures, implying substantial changes in the life style of the species). Some of the most noticeable insular evolutionary changes produced a variety of unusual taxa. Among amphibians, the subterranean Hydromantes from Sardinia, with four species still living on the island, displaying a ...

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