June 18, 2009

Britain Mammoths Survived Much Longer Than Once Thought

According to new radiocarbon dating evidence, woolly mammoths lived in Britain as recently as 14,000 years ago.

Dr. Adrian Lister acquired new dates for mammoth bones that had been excavated in 1986 in the English county of Shropshire.

His study published in the Geological Journal shows that the radiocarbon results from the adult male and four juvenile mammoths from Condover, Shropshire, reveal that the mammoths were in Britain for more than 6,000 years longer than had been believed.

Experts think that mammoths may have met their end when forests infringed on the grassland habitats where they grazed.

Researchers had previously supposed that mammoths disappeared from North-West Europe somewhere between 21,000 and 19,000 years ago, when a climatic freeze known as the last glacial maximum (LGM) wreaked havoc on their habitat. Britain's mammoth populations may very well have disappeared with this big chill.

The giant mammals prospered through the initial phase of the last Ice Age but were unable to endure the bitterest chill despite their thick coats.

The British mammoths traveled south and east towards warmer climates, across a land bridge to continental Europe when sea levels were up to 328 feet below what they are now.

However, the new study shows that they were not permanently gone, but rather returned once conditions allowed it and remained in southern England until 14,000 years ago. 

"What this usually means is that (mammoths) die out locally and then re-emigrate from refugia somewhere else," Dr Lister told BBC News.

The specimens have undergone radiocarbon dating before, however a Natural History Museum researcher used a new method of purification developed at Oxford University called ultra-filtration, which provided a better purification to get more accurate ages for the Condover fossils.

"The big issue with all radiocarbon dating is contamination from different sources. You have to be sure the sample you extracted from the fossil is absolutely pure"¦there have to be methods for purifying the sample that is extracted from the bone," said Dr Lister.

"Various bone specimens that were dated before they developed this new purification method have been shown to be out by a significant amount. Not always, but often. What they do is re-run the sample using the new method and obtain a more accurate date. That's what we did here."

Other large mammals disappeared as the Ice Age came to an end such as the woolly rhino, bison and giant deer.

As these species dwindled and vanished from the Earth, human populations were on the rise.

With similar extinctions of what are referred to as "megafauna" throughout the world around the same time, scientists are questioning the roles that climate change or human hunting may have played in their demise. 

Though there have been no signs of humans ever occupying the Shropshire site, it is still a great possibility that humans were in Britain at the same time as these most recent mammoths. 

Dr Lister said that humans might have succeeded in finishing off some of the remaining mammoth populations in Siberia, but he does not consider people to have been the primary cause of megafaunal extinction at the end of the last Ice Age.

Lister said the continuance of these mythic animals in today's central England is likely an example of "extinction lag," where small pockets are able to survive even when the species as a whole has disappeared.

The Ice Age provided a climate conducive to copious grasslands in Europe keeping tree growth to a minimum.

Then, with warming climates, forests began spreading north, choking out the once abounding grassland habitats where the giant beasts grazed.

According to Dr. Lister, it can't be said that the climate is responsible for affecting the animals directly, but rather the affect the climate had on the vegetation that was crucial to their survival.

Mammoths first appeared in the Pliocene Epoch, about 4.8 million years ago.

One population lived on in isolation on Russia's remote Wrangel Island until about 5,000 years ago, making them the most recent surviving population known to science.

Image Courtesy Jonathan Blair/Corbis


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