Woollies in Hiding!

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The woolly mammoth is probably one of the most widely recognised extinct animals of the Pleistocene. During the Pleistocene-Holocene transition, a succession of local extinctions took place, probably due to a combination of human and climatic pressures (there is still debate over what actually caused them to become extinct). The last mammoth refugia were once thought to be in the Siberian Arctic and the Arctic Islands (Vartanyan 1995). However, evidence has been found of small isolated population of woollies on Wrangel Island (click here for more information on Wrangel Island) well into the Holocene epoch. Vartanyan 1995 used ¹⁴C dating to estimate the ages of mammoth tusks, teeth and bones preserved in sediments on Wrangel Island. Their results indicated that mammoths were present on Wrangel Island in the mid-Holocene, up to 6000 years after their estimated extinction in Siberia.

The population of mammoths on Wrangel Island became isolated at around 9000 years BP due to rising sea levels at the end of the Pleistocene (Vartanyan et al 2008). Wrangel Island must have provided suitable conditions for this population of mammoths in order for them to persist here for such a long time after they had become extinct. The mammoths here were much smaller due to limited food supplies and have been referred to as ‘dwarf mammoths’ (although I’m sure they were probably still massive!) – see Vartanyan et al1993. 

Nystromet al (2010) investigated the genetic consequences of this isolation on the mammoth population of Wrangel Island by analysing 741 base pairs of mitochondrial DNA. They found that there was an initial loss in genetic variation that coincided with the time of their isolation on Wrangel Island (for a reminder of what genetic variation means click here), but after that initial loss the population of mammoths remained genetically stable (if that’s even a proper term!) despite having been isolated in refugia for so long. This led them to conclude that this population of mammoths did not gradually become extinct due to genetic reasons, but the stable population became suddenly became extinct due to a relatively abrupt change in their environment (either climatic or human in nature).

This may be a stab in the dark here but if cold-loving woolly mammoths existed in refugia before becoming extinct, then could comparisons be made between the fate of the mammoths and the fate of the polar bears? I realise that the two cases are significantly different and woolly mammoths once had a much wider distribution than polar bears ever have but the mammoths on Wrangel Island were isolated and subject to unique selection pressures, meaning that they adapted to possess distinctive characteristics, which holds some resemblance to the population of brown bears from which their Arctic cousins evolved (although a new species of mammoth was not created). Polar bears and mammoths are/were both cold-adapted species who are/were under threat from changing climatic conditions and human interaction – could climate change and hunting of polar bears drive this refugial population to extinction like possibly it did with the mammoths? Things aren’t looking promising…