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EXTINCTION OF MAMMOTHS
IN AMERICA
Of all the
prehistoric mega fauna on Earth, few have captured the imagination as
thoroughly as the woolly mammoth. Scientists have researched the feasibility
of cloning mammoths for decades, but knowing how and why they died out would
tell us a great deal about the feasibility of restoring the species today.
Research on the last-surviving mammoth population in North America reveals that
this group of animals probably did not die as the result of human hunting or
a loss of food. Woolly mammoths
became extinct between 10,000 and 14,000 years ago, along with the majority
of the Pleistocene megafauna. However, there are two known exceptions.
Mammoths persisted on two islands: Wrangel
Island, a Russian island in the Arctic Ocean, and Saint Paul Island, off the Alaskan
coast. The latter is the last-known location where mammoths survived in North
America (3600 BC), while the Wrangel population lived until about 2000 BC. The two hypotheses for why megafauna like the mammoth went
extinct are climate change and hunting by humans. As the climate warmed, humans expanded into new territories
that were formerly blocked by ice or too harsh to sustain life on an ongoing
basis. The populations on Saint Paul
and Wrangel survived as long as they did probably because they were isolated
from humans and therefore were not hunted. One possible explanation for the Saint Paul mammoths’
eventual extinction would be the glacial melt that created the island in the
first place. The oceans rose, turning Saint Paul into an island and trapping
a group of mammoths in the process. Despite being isolated on a comparatively
tiny rock, the mammoths survived for thousands of years and long after the
island’s modern shorelines were established. Glacial melt might have isolated
the population, but it is not what destroyed the population. Research teams collected mammoth remains from a cave on
St. Paul and took sediment samples from a nearby lake. They analyzed the
sediment samples searching for the spores of fungi that live on the island
and preferentially reproduce in animal dung. Elephants are famous for
producing copious amounts of dung and the sediment samples
reflected this up to about 5,600 years ago. Other analyses of the sediment
cores showed that vegetation and plant life on the island had remained
constant over time as well, but the mammoths did not perish due to a lack of
food, either. Thirst, not hunger may have have doomed the mammoth
population. Instead, the extinction
coincided with declining freshwater resources and drier climates between
7,850 and 5,000 years ago, as inferred from sedimentary magnetic
susceptibility, oxygen isotopes, and diatom and cladoceran assemblages in a
sediment core from a freshwater lake on the island, and stable nigrogen
isotopes from mammoth remains.
Contrary to other extinction models for the St. Paul mammoth
population, this evidence indicates that this mammoth population died out
because of the synergistic effects of shrinking island area and freshwater
scarcity caused by rising sea levels and regional climate change. Saint Paul Island
lacks any spring or source for fresh water, which means there was no way to
restore its supply. As the climate dried, the amount of water available to
the mammoths declined, while rising sea levels allowed salt water to
penetrate the soil from below. A comprehensive analysis on the diatom fossils
present within the sediment cores showed evidence that the types of diatoms
in the water had changed dramatically over time. Older core samples showed
evidence of diatoms — single-celled algae — that preferred freshwater and a
depth of several meters. This type of diatom was plentiful in core samples
dated to about 5,800 BC and became much less common thereafter before
vanishing altogether. The diatoms that replaced it are from species that
thrive in shallower waters with a higher concentration of salt. In short, the mammoths died out at a time when the island
still had enough plants to feed them and space for them to live on, but when
the quality and amount of water had declined. Because of this thirst ultimately killed the mammoth
population. Climate change can damage
ecosystems without inundating an area.
Freshwater contaminated by saltwater seeping in from the ocean can
kill plants and effectively poison animals, leading to dramatic ecological
changes in a relatively short period of time. |