Science makes DNA breakthrough in the tooth of a mastodon


Jul 22, 2007

A fossilised tooth found in a swamp has allowed scientists to work out the DNA of a primitive North American elephant

SCIENTISTS have worked out part of the genetic structure of the mastodon, a giant primitive elephant, after finding DNA preserved in the fossilised tooth of a beast that died up to 130,000 years ago.

The creature is thought to have roamed the forests and plains of North America before dying and sinking into a swamp that preserved its tissues.

Researchers were hoping its teeth might have preserved enough of the DNA for them to recover lengthy chunks of it, and this week they will publish research detailing how their hunch has paid off. The find has allowed them to reconstruct the entire sequence of the DNA found in the creature’s mitochondria, the parts of cells concerned with energy production. It is thought to be the oldest DNA ever to have been recovered and decoded in this way.

The information obtained has shed new light on the ancestry of mastodons and mammoths, both now extinct, as well as on the origins of the three surviving elephant species - the African, the forest elephant, also from Africa, and the Asian.

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Mastodons were around the same size as modern elephants but were much more heavily muscled and had furry coats to protect them from cold.

“Using the mastodon’s mitochondrial genome sequence, together with sequences from two African elephants, two Asian elephants, and two fossil woolly mammoths, it was shown that mammoths are more closely related to Asian than to African elephants,” said Michael Hofreiter, a researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the research. “This shows the power of genetic data to clarify relationships.”

The ancestry of the elephant has long been a source of fascination for biologists. Fossil evidence shows it began in Africa around 50m-60m years ago with moeritheres, pig-like creatures with long snouts.

These animals evolved into a range of other species, many of them much larger, and spread across the globe, inhabiting every continent except Australasia and Antarctica.

The four-tusked trilophodon appeared 26m years ago and lasted until 2m years ago in Eurasia, Africa, and North America. Modern humans, by contrast, evolved only around 200,000 years ago.

Biggest of all was the imperial mammoth, which adapted to the cold in Eurasia, Africa, and North America during the Pleistocene epoch 2m years ago. They appear to have survived until just a few thousand years ago and early humans would have been familiar with them.

Hofreiter suggests the evolution and extinction of many elephant species may be closely tied up with the spread of the human race.