Phylogeny and Paleobiogeography of Short-Tailed Shrews (Genus \u3ci\u3eBlarina\u3c/i\u3e)

Dental measurements of Pleistocene and Holocene shrews of the genus Blarina were analyzed in a multivariate assessment of phylogeny and paleobiogeography of the genus. Blarina brevicauda, or an indistinguishable precursor, apparently was the ancestral form. Two semispecies, brevicauda and talpoides, are recognizable early in the fossil record; these two phena probably appeared as a result of increasing diversity\u27in the environment of the late Irvingtonian. Evidently, repeated fluctuations of climate and the subsequent changes in range have not been sufficient to cause the cessation of gene flow necessary to complete speciation. A second species, B. carolinensis, appeared in the mid-Irvingtonian. Although its original distribution is unclear, the species apparently evolved in temperate conditions in the south. Increased continentality following the Wisconsinan glaciation resulted in the appearance of the species B. hylophaga, which is restricted to the southwestern part of the range of the genus. Sympatry of the two semispecies of B. brevicauda and/or sympatry of B. carolinensis and B. hylophaga detected in some of the paleofaunas are thought to be the result of periods of more equable climate. Post-Wisconsinan fluctuations of climate are the probable cause of the eastward restriction of the genus and the zones of sympatry observed between Holocene phena. Fossils of Blarina have been found in warm-moist and cool-moist faunas. The fossil record (late Blancan-Rancholabrean) and paleoecology of the genus are summarized