CALIFORNIA ISLANDS PYGMY MAMMOTHS (MAMMUTHUS EXILIS): THEIR ORIGIN, AGE, SIZE AND EXTINCTION

Pygmy mammoths (Mammuthus exilis) have been recognized on the northern Channel Islands of California since a 1873 paper resulting from a Coast and Geodetic Survey. Several papers were produced nearly 50 years later, followed by two dissertation studies in the 1970's and 80's. The discovery of a nearly complete skeleton of an adult male (M. exilis) in 1994 initiated an on-going program of locating, mapping, selected collection, and analyses of the mammoth remains. The presence of limited specimens of the continental mammoth (Mammuthus columbi) reflects the possibility of late migrations to the island, or remnant, refugial continental forms. M. columbi remains comprise about 10 % of the specimens recorded. No M. exilis remains are known from the continental mainland. Calculations of the center of gravity for both forms reveals the slope of island terraine accessible to the pygmy form, but denied to the larger, continental form. This provided an environmental factor favoring smaller size. Radiocarbon dating indicates the presence of pygmy mammoths for more than 47,000 years (near the upper limit of radiocarbon dating) until the arrival of humans on the islands about 11,000 radiocarbon years ago. To date, no actual kill sites or processing areas have been recognized. However the human remains from Arlington Springs, Santa Rosa Island, and pygmy mammoth remains from nearby Garanon Canyon, Santa Rosa Island indicate presence of extant island mammoths at the time of arrival of pioneering human populations.