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Giants and pygmies: Mammoths of Santa Rosa Island, California (USA)
- Agenbroad, Larry D.
- Quaternary international 2012 v.255 pp. 2-8
- islands, skeleton, teeth, thorium, uranium, California
- Mammoth remains have been known from the northern Channel Islands of California since 1856. Initially, it was considered that there were several species of mammoths on the islands. It has now been determined that there are only two species: 1) Mammuthus exilis, the island pygmy mammoth, and 2) Mammuthus columbi, the giant, continental (mainland) mammoths which were the ancestral mammoths from which M. exilis was derived. Discovery and recovery of the most complete skeleton of M. exilis, in 1994 prompted new research efforts and a numerical chronology for the pygmy mammoths, ranging from 11,030 BP to greater than 200,000 a by U/Th (Uranium/Thorium). Little attention had been paid to the chronology of the less abundant M. columbi remains. Uranium/Thorium dates on two M. columbi teeth yielded dates of 28,000 ± 2000 a, and 64,500 + 7400/−6900 a. If the U/TH dates are valid, they indicate a long history of shared island occupation, with M. exilis, or repeated migrations of M. columbi from the mainland to the islands. No M. exilis remains have been discovered on the mainland. In 2009 additional efforts to date the Columbian mammoth remains were initiated, to ascertain whether they were: 1) contemporary with the pygmy mammoths; 2) represented remnants of the founding population; or 3) represented late migration from the North American mainland.