Radiocarbon evidence of mid-Holocene mammoths stranded on an Alaskan Bering Sea island

Island colonization and subsequent dwarfing of Pleistocene proboscideans is one of the more dramatic evolutionary and ecological occurrences1,2,3, especially in situations where island populations survived end-Pleistocene extinctions whereas those on the nearby mainland did not4. For example, Holocene mammoths have been dated from Wrangel Island in northern Russia4. In most of these cases, few details are available about the dynamics of how island colonization and extinction occurred. As part of a large radiocarbon dating project of Alaskan mammoth fossils, I addressed this question by including mammoth specimens from Bering Sea islands known to have formed during the end-Pleistocene sea transgression5. One date of 7,908 ± 100 yr bp (radiocarbon years before present) established the presence of Holocene mammoths on St Paul Island, a first Holocene island record for the Americas. Four lines of evidence—265 accelerator mass spectrometer (AMS) radiocarbon dates from Alaskan mainland mammoths6, 13 new dates from Alaskan island mammoths, recent reconstructions of bathymetric plots5 and sea transgression rates from the Bering Sea5—made it possible to reconstruct how mammoths became stranded in the Pribilofs and why this apparently did not happen on other Alaskan Bering Sea islands.