Abstract
Packrat (Neotoma spp.) middens in rock-shelters provide important paleoecological records for the desert regions of North America. Specimens of various arthropod species accumulate in the middens and are cemented into a black, tarry mass by packrat urine.We collected a variety of ants, including the genera Labidus, Pseudomyrmex (?), Aphaenogaster, Crematogaster, Pheidole, Pogonomyrmex, Solenopsis, Trachymyrmex, Liometopum, and Camponotus in packrat middens from the Chihuahuan Desert. Our data suggest a climatic change in the Chihuahuan Desert from mesic to arid during the past 45,000 years. The coniferous forest, oak-juniper woodland of the early Holocene changed to desert-grassland about 8250 radiocarbon years before present (yr BP), with a corresponding shift in ant species composition. By about 7500 yr BP, the presence of several arid adapted species suggests the establishment of desert environments. Finally after about 2500 yr BP, we see the occurrence of primarily desert adapted ant species in the Chihuahuan Desert, although mesic adapted species continue to occur in moist "islands" within the area. The paleoenvironmental data derived from the ant fossil records agrees closely with previous reconstructions based on other arthropods.