Fossil Evidence Bearing on Southwestern Mammalian Biogeography

Harris, Arthur

The fossil record from the Wisconsin (Pleistocene) of Trans-Pecos Texas, New Mexico, Arizona, and southern Nevada indicates that most of the region north of a line from northwestern Arizona southeast to the Guadalupe Mountains of Trans-Pecos Texas supported habitats suitable for taxa now occurring in the high Southern Rockies of northern New Mexico and southern Colorado. South of this line, highlands were isolated from many of these taxa throughout the late Wisconsin by lowland barriers. However, many species of mammals that now occur in the Southern Rockies only in high-elevation habitats, but that occur in nonboreal habitats farther north, ranged far south of this line. Some taxa now typical of the Great Basin also occurred far to the south, some to the Mexican boundary and southeastern New Mexico. Following full-glacial conditions, slightly warmer and more mesic summers allowed eastern and southern grassland taxa to penetrate westward, but with little loss of northern and Great Basin species of mammals. The full-glacial situation for lowland taxa is less well known; some had distributions similar to now, but others were restricted greatly. The present ranges of many taxa probably were reached early in the Holocene, but some taxa may have survived in refugia into the late Holocene. Several lowland taxa expanded north and west of their present ranges during the middle Holocene under conditions warmer and possibly more moist than today.

Fossil Evidence Bearing on Southwestern Mammalian Biogeography

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