 |
LIFE SCIENCES
 Ancient mastodon tooth clarifies elephant lineage
An international team headed by European scientists has been able to clarify the lineage of modern elephants, thanks to improved techniques for extracting DNA from a tooth, dated between 50 000 and 130 000 thousand years old. In a new paper in the open access journal PLoS, Michael Hofreiter from the Max Planck Institute for Evolutionary Anthropology in Germany and colleagues from Switzerland and the United States, described the sequencing of the complete mitochondrial genome of an extinct relative of living elephants, the mastodon (Mamut americanum), which diverged around 26 million years ago.
 | | DNA was extracted from a Mastodon tooth that was at least 50 000 years old. |
|
The sample came from a mastodon tooth that had been stuck in permafrost since the Pleistocene, at least 50 000 years ago. The creature becomes only the third extinct taxon for which the complete mitochondrial genome is known, joining the woolly mammoth (which is superficially similar in appearance), and a number of species of Moa, a giant flightless bird from New Zealand.
Carrying out comparisons using the mitochondrial genome sequences, together with sequences from two African and two Asian elephants, and two frozen woolly mammoths (obtained from previous work), the relationships between these group members have been made much clearer. The data indicates that mammoths are more closely related to Asian than to African elephants. Results also suggest that African elephants in fact comprise two species, forest and savannah, which have been diverging for about four million years.
The study demonstrates the power of genetic data to clarify interrelationships, even in the case of well-studied taxa. The researchers used the information from the mastodon tooth as a reference point, enabling them to estimate that the time of divergence of African elephants from Asian elephants and mammoths, would have been about 7.6 million years ago. The divergence between mammoths and Asian elephants was estimated to have taken place about 6.7 million years ago.
These dates are strikingly similar to the diversification of African primates into chimpanzees, gorillas and humans. The paper’s authors suggest that the speciation of mammoths and elephants and of African great apes and humans may have been triggered by a common cause, such as a change in environmental conditions. Despite these similarities in divergence times, the substitution rates within primates are more than twice as high as for the group containing the mastodon, woolly mammoths and African and Asian elephants, indicating that the molecular clock ticks differently for different taxa.
|
|
More information:
Max Planck Institute for Evolutionary Anthropology
PLoS article
|
|
