The Origin of Island Mammoths and the Quaternary Land Bridge History of the Northern Channel Islands, California
Johnson DL. 1978. The Origin of Island Mammoths and the Quaternary Land Bridge History of the Northern Channel Islands, California. Quaternary Research. 10(2):204-225
Pygmy proboscidean remains of Mammuthus exilis occur abundantly in late Quatemary deposits on the Northern Channel Islands, California. On the assumption that ancestral elephants could not have swum to the islands and must therefore have walked out, various land bridges have been hypothesized that link the northern islands to the mainland by a peninsula. Geological evidence for a land bridge, however, is lacking, and new evidence shows that elephants are excellent swimmers and skilled at crossing watergaps. The Santa Barbara Channel was narrowed to only 6 km during glacially lowered sea levels. Modem elephants swim much further, and at speeds ranging from 0.96-2.70 km/hr. Motives for California elephants to cross Pleistocene watergaps are inferred from motives that lead modem elephants in Asia and Africa to cross watergaps. These are the visual and olfactory sensing of islands and of insular food during times of drought or fire-induced food shortage. Diminutive size of M. exilis principally reflects lack of island predators, an adaption to periodic food stress in a finite forage area affected by periodic drought and fire, and an adaptation for keeping population numbers high to maintain genetic variability and to ensure survival despite accidents. A late Quatemary scenario describes the environmental setting of the Santa Barbara Channel and the conditions that led to proboscidean dispersal to the preexistent super-island Santarosae.
- Type
- Journal Article
- Authors
- Johnson, Donald
- Units
- CHIS
- Keywords
- Channel Islands CA, Paleontology, Pygmy Mammoth (Mammuthus exilis)