Abstract
Abstract The Eurasian otter (Lutra lutra) exhibits the widest range among the Lutrinae, encompassing 11 extant subspecies across Eurasia and North Africa. However, recent mitochondrial DNA analyses have revealed distinct lineages that do not correspond to current subspecies classifications. To evaluate the degree of morphological divergence and identify populations potentially representing evolutionarily significant units, we used three-dimensional geometric morphometrics to examine 207 crania sampled across the species range. We digitized 30 anatomical landmarks along with nine curves using sliding semi-landmarks on three-dimensional models of crania. The morphometric analysis demonstrated significant differences in cranial size and shape between sexes and subspecies. Specifically, L. l. nair exhibited the most divergent cranial morphology and should be recognized as an evolutionarily significant unit. The Asian subspecies L. l. chinensis, L. l. barang, and L. l. nair displayed morphological affinities and were characterized by diverging traits from the nominal subspecies. Of the three subspecies described for the Transhimalaya, only L. l. aurobrunnea was clearly distinct from L. l. lutra. These patterns are likely to reflect evolutionary responses to ecological adaptation and geographical isolation, highlighting the need to explore the genetic structure of the Eurasian otter and reassess subspecies boundaries.