Abstract

Proboscidean remains on the Northern Channel Islands of California include those of the ancestral Mammuthus columbi from the mainland, and a smaller, more variable derived form, Mammuthus exilis, endemic to the islands. Early researchers often cited the mammoth remains as evidence for a land bridge between the islands and the mainland. However, seismic profiles from the Santa Barbara Channel have indicated that an island-mainland connection was unlikely during the Quaternary, thereby suggesting that the animals swam the channel. The impetus for the proboscidean migrations is uncertain; speculations include fire or drought-induced food stress on the mainland combined with the animal’s affinity for water. In the absence of large carnivores on the island, large size in mammoths was no longer advantageous, and smaller forms were favored as island vegetation became limited. The apparent flexed posture of M.exilis may have been a consequence of size reduction and allowed the animal maneuverability in areas inaccessible to its large ancestor. Progenesis and stunting as possible dwarfing mechanisms are under investigation, whereas achondroplasia has been ruled out. With a limited sample of associated bones and a poor idea of the chronology of events on the islands, an understanding of many aspects of the island mammoths awaits future work.