Monday, July 23, 2007

Out of Africa - the evolution of the Elephant

Approximatly 50-60 million years ago, mammals with the approximate size of current day pigs, were the roots of the proboscideans from which modern representatives evolved from. Based on both morphological and biochemical evidence, the manatees, dugongs, and hyraxes are the closest living relatives of the today's elephants. It is amazing to consider that given the different sizes, external appearances and the fact that they occupy completely different habitats they are all related to one another.

It has been shown that mammoths are more closely related to Asian than to African elephants. This research is the result of using the mitochondrial genome sequence, together with sequences from two African elephants, two Asian elephants, and two woolly mammoths.

The complete mitochondrial genom sequencing of the mastodon (Mammut americanum) was recently announced. This is a recently extinct relative of the living elephants that diverged about 26 million years ago.

How was the mitochondrial sequence obtained?
The sequence was obtained from a tooth dated to 50,000--130,000 years ago. The mastodon becomes the third extinct taxon for which the complete mitochondrial genome is known, joining the woolly mammoth, and several species of Moa, the giant flightless Australasian bird.

Some Results
Researchers used the mastodon data as a calibration point, lying outside the Elephantidae radiation (elephants and mammoths). This has allowed them to estimate the time of divergence of African elephants from Asian elephants and mammoths at about 7.6 million years ago, and the time of divergence between mammoths and Asian elephants at roughly 6.7 million years ago.

Common Cause for divergence?
The dates found in these divergences are very similar to the divergence time for humans, chimpanzees, and gorillas. This raises the possibility that the speciation of mammoths and elephants and of humans and African great apes had a common cause.

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