A New Irvingtonian Water Shrew (Insectivora: Soricidae) from Nuckolls County, Nebraska: Systematics, Functional Morphology and Paleoecology

Eight species of three genera of shrews were recovered from the Albert Ahrens Site, Nuckolls County, Nebraska. Based on dental morphology, biomechanics, and paleoecology, one of these is believed to represent a previously undescribed species of water shrew. It closely resembles the modern North American water shrews, Sorex palustris and Sorex bendirii, in overall morphology but differs from both by having a taller coronoid, more anteroposteriorly compressed unicuspids, less constricted snout, and a bite force index (BFI) that falls between S. palustris and S. bendirii. Twelve of 33 quantitative characters significantly distinguish S. sp. A as a new species. The BFI and I1 morphology, in addition to fish remains and an area of Sorex sympatry in central Canada, suggest a similar paleoecology of cool, moist boreal parkland habitat. The Albert Ahrens Site is important geologically and paleontologically because it lies stratigraphically higher than a nearby mid-Pleistocene ash bed and its fauna is similar to the Cudahy local fauna (I. f.), Meade County, Kansas. Ash clasts within the highly fossiliferous bone pebble matrix have been found to match exactly the nearby ash bed. Radiometric dating and mineralogic examination of samples of this ash reveals that the source is the 0.6 Ma Lava Creek B Ash, making the fossil site younger than the Cudahy l. f. This temporal relationship to the Cudahy I. f. is important to understanding the evolutionary development and paleoecology of certain long-tailed shrews (genus Sorex) in the Midwest.