By their own very nature, islands are natural laboratories where evolutionary outcomes seem to exceed the limits of imagination. Stubby and flightless birds, dwarf elephants and hippos, and giant mice are some of the bizarre examples. Those morphological modifications are not the result of random variation but are triggered by the specific ecological conditions of the islands (absence of terrestrial predators and low level of competition for food and space). In some occasions, these conditions do not lead to a particular shift in body size, but instead to a diversification event, resulting in a disparity of forms, such as the case of Darwin’s finches in Galapagos. The island of Crete (Greece) housed one such diversification, that of the enigmatic extinct Pleistocene deer. This genus (Candiacervus) evolved into eight species in six size groups, ranging from ~28 to ~245kg in body mass, in less than 1 million years. In CREDE I will explore this unusual disparity of body size in Cretan deer to understand the evolutionary mechanisms behind species radiations in mammals. Despite advances over the years in knowledge on this lineage, mainly focusing on dwarf or giant species, we know little about the factors underpinning this level of diversity. In CREDE I will employ my expertise in deer bone histology together with the novel application of 3D image analysis to examine bone microstructure of Cretan deer, and thus, obtain data about their life strategies (age at maturity, pace of growth, longevity). Moreover, the use of stable isotope will provide new integrative data on the ecological and dietary preferences of the different species. Finally, the combination of both approaches will shed light on diversification of mammal lineages on a macroevolutionary scale, presenting a comprehensive framework for interpreting mammalian evolution.