Environmental Controls

The wood rat fauna from the Pit includes four of the five species of wood rats that now live in southeastern Colorado. Four of the five southeastern Colorado species live in the vicinity of Pueblo, about 120 km to the southeast of Porcupine Cave at an elevation of 1489 m, and extend eastward across the Great Plains. The fifth (Neotoma cinerea) is the species that makes up the majority of the Porcupine Cave sample and now lives in the cave area, as well as elsewhere in the mountains at elevations as low as 1830 m. Three other southeastern Colorado species found in the cave deposits are N. micropus, N. mexicana, and N. floridana. A southeastern Colorado species that does not occur as fossils in the cave is Neotoma albigula. Instead N. stephensi is the fifth wood rat species in the Pit fauna. Given the age interpreted for the Pit sequence (circa 780,000 to as old as 1 million years), the wood rat fossils represent the earliest known occurrence of the five Neotoma species.

As noted previously, N. albigula now lives in the deserts from the Imperial Valley of California eastward across Arizona and New Mexico (avoiding the high Mogollon Rim and the southern Sangre de Cristo Mountains) almost to Austin, Texas, and southward to Michoacan in central Mexico. Only its northernmost range is in extreme southwest and southeast Colorado. It is a species of hot deserts with hot summers and little or no winter snow. Its absence in the Pit fauna suggests that at least one of these conditions did not exist around Porcupine Cave during deposition of the Pit fauna.

N. stephensi now lives between about 1200 m and 2440 m elevation and about 200 km farther south (latitudinally) than Porcupine Cave. Except for N. stephensi, all the wood rat species of the Pit fauna live nearby, around 80 km to the east near Colorado Springs and at or below 1830 m elevation.

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