Fossil Mammals

The dry valleys of the Colorado Plateau that today support only a rather meager-looking desert scrub vegetation do not look like good habitat for mammoths, horses, sloths, musk-oxen, and camels. But because of the abundance of dry caves and rockshelters, the vertebrate fossil record for the late Pleistocene is remarkably well preserved, giving us much information about the existence of these animals and their former habitats.

The large mammals that roamed the region during this time were well adapted to its ice-age environments. For example, the Columbian mammoth, which lived on the Plateau during the last glacial period and was a member of the elephant group (proboscideans), had teeth that consisted of a set of large, flat molars. These teeth had row after row of tightly spaced grinding surfaces, meant for chewing grasses and other herbaceous plants. Mammoths were roughly the size of the modern Asian elephant, and probably consumed huge amounts of vegetation every day, a diet that argues that highly productive plant communities existed in the Southwest during this time. It doesn't take a great deal of additional moisture to turn desert scrub into semidesert grassland or steppe, where grasses are more common and shrubs more luxuriant.

These animals probably survived on the Colorado Plateau during millions of years of glacial-interglacial cycles. Adapted as they were to colder temperatures and greater moisture, the relatively brief interglacial warm periods must have been difficult for them, but the extinction of this megafauna on the Plateau and elsewhere coincided not only with the end of the last ice age but with the arrival of humans on the North American continent. How responsible humans were for this sea change in the North American fauna is the subject of great debate. The evidence needed for its resolution may well emerge from the fossil bones of these magnificent creatures.

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