Evolution of marmots (Rodentia, Sciuridae): combining information on labial and lingual sides of the mandible

The morphology of the lingual side of the mandible was analysed in the genus Marmota. Adults from 12 of 14 living species were compared using geometric morphometric techniques. The information on the lingual side was then combined with that of the labial side from a previous analysis. The combined dataset is the most complete description of a marmot mandible ever used in an interspecific comparison in this genus and it represents the second morphological study ever realized that includes a large sample with all marmot species. The study confirmed the uniqueness of M. vancouverensis for mandible morphology, with atypical traits likely to have evolved in a relatively young but small population of marmots isolated on the Vancouver Island since the end of the Pleistocene (10 000-100 000 ybp), stressing the importance of a strong effort to save this species from extinction. Marmota olympus also has a distinctive mandibular trait undetected in a previous analysis using information on the lingual side only. The Olympic marmot has a longer evolutionary history but it is presently found only in the Olympic Peninsula and shares with M. vancouverensis a similar history of geographic isolation and population bottlenecks. Genetic bottlenecks might have profoundly affected marmot morphological evolution and may have increased the rate of shape change in marmot radiations. Both the analysis of the lingual side alone and the combined dataset (lingual and labial information) failed to clearly discriminate the two main marmot subgenera but the combined description of the mandible supports the similarity of the two main species (M. caligata and M. flaviventris) of the subgenus Petromarmota, and the proximity of the North American M. monax to Palaearctic marmots. Surprisingly, the analysis of the lingual side indicated that M. canitschatica and M. marmota have unusual traits for the subgenus Marmota. At least for the latter species, this finding is congruent with peculiarities in fur and parasitic relationships, and may be related to an ancient phylogenetic origin for M. marmota.