Crete was completely submerged during the Pliocene, and gradually emerged in the Early Pleistocene. New and empty islands like these are normally colonized overseas by sweepstake dispersal, which means that only a limited number of taxa is able to reach the island. This results in an unbalanced mammal fauna, as a rule consisting of only elephants, hippopotamus, deer, cattle, rodents, insectivores and sometimes otters. After successful colonization, as a rule a fast evolutionary change takes place, which can be explained as an adaptation to the restricted island environment. As a result, island faunas are very different from mainland faunas, but similar to each other. Crete is no exception to this general pattern, and during the Pleistocene there were two successive endemic mammalian faunas. The first (the Kritimys-biozone) is characterised by a dwarf mammoth, a dwarf hippopotamus and a giant mouse. The second (the Mus-biozone) is characterised by a dwarf elephant, a dwarf deer (next to medium and large-sized deer) and a large mouse. The reason for the dramatic faunal turnover between the two biozones is unknown, but may very well have been related to a significant sea-level drop. This decreases the distance between the now larger island and another firm ground. The second fauna got extinct just before or after the arrival of the first humans. Problems of dating and the lack of paleolithic artefacts or human remains obscures this point. In any case the fauna of the second biozone was already completely extinct at Aceramic Neolithic and Minoan times, and replaced by newcomers who came together or along with the humans.
Read more in VAN DER GEER A.A.E., DERMITZAKIS M., DE VOS J. (2006). Crete before the Cretans: the reign of dwarfs. Pharos 13: 121-132. Netherlands Institute at Athens, Greece. Free pdf [ 2,197 kb] at http://users.uoa.gr/~geeraae/publications/2006-pharos-crete.pdf .