Glis) clustered the new haplotypes into the Iranian lineage which hold a sister position against all other fat dormouse haplotypes from Europe and Asia Minor. Morphometric geometric analysis of the mandibles from all parts of its distributional range also confi rms such deep divergence. The divergence between these lineages suggests a fragmentation event of an ancestral population at 5.76 million years ago (mya) at the end of the Miocene. This early evolutionary divergence was possibly triggered in the Middle East by dramatically divergent environmental conditions during the Messinian Salinity Crisis. We suggest a long-term persistence of the Iranian lineage in the Hyrcanian refugium which is consistent with a high number of endemics along the southern Caspian coastal areas. Extreme morphological diff erences in the species can be seen in the Hyrcanian refugium. Our results showed that Iranian dormice have on average more nipples (mean = 12.57 ± 1.024) than their counterparts from other parts of the world. The litter size in the Iranian fat dormouse is 7.85 ± 0.89 which is evidently more than reported in other populations. It seems that such large morphological divergence is related to the evolutionary history of the species in the Hyrcanian refugium
