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Shrews of the Cryptotis genus (Eulipotyphla: Soricidae) of the late Pleistocene in the Ecuadorian Andes

Abstract:

During a paleontological excavation in Chalán Gorge (Chimborazo province), some fossil of micromammals where registered, including, five femurs, four humerus, eight pelvic bones and a fragment of maxilla of Cryptotis, with P4, M1 and M2 dental pieces. The fossils where collected in higher levels of cangagua formation of upper pleistocene. Nine measures of humerus and femurs fossil where obtained, and compared with the current Ecuadorian species. The results showed that the fossils belonged to Cryptotis niausa species, by the arcuate shape of the anterior segment of the mesopterygoid fossa, as well as similar dimensions in femurs, humerus and maxillary bone of C. niausa. In the upper pleistocene C. niausa was distributed 160 km south of its current distribution. This species is not currently distributed in the find locality, because the climate is warmer and drier than the wet Andean grasslands where C. niausa now lives. This finding demonstrates that Chalán Gorge had other vegetation in the late pleistocene during the second and third interglacial ages, similar to current Andean grasslands whose "pajonales" are above 3200 meters. Morphological analysis of fossil C. niausa shows individuals with bones structure and muscle more robust than the current populations. Some Cryptotis fossils individuals have wider dimensions of the femurs and humerus, associated with an increased ability to dig their burrows and channels on hard soils result of strong volcanic activity.