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Visualization of the Day (#1): Mammal "Supertree"

chart-mammals.jpg An international team of researchers has produced a new family tree for mammals, showing relationships between different mammal groups and when they diverged from each other. According to Kate Jones, from the Zoological Society of London:
The [supertree] is a new way of showing all the mammal species on the planet, starting with a common ancestor. Species relationships can be inferred from morphological characteristics and genetic sequences.

If we had done this from scratch, we would have had to get molecular and morphological data for 4,000 different species.

What we did instead was use already published information from hundreds of researchers around the world. We used a new technique called supertree construction which allows us to get all the information that's out there, re-code it and re-analyse it as if it's all part of one dataset.

The most surprising revelation to emerge from the project? Evidence that diversification of mammals may have occurred much earlier than previously thought:

Throughout the Cretaceous Period, when dinosaurs walked the Earth, mammals were relatively few in number, and were prevented from diversifying and evolving in ecosystems dominated by the ancient reptiles. [. . .] Under this model, placental mammals split into major sub-groupings, which originated and rapidly diversified after the mass extinction event - thought to have been caused by an asteroid or comet striking Earth 65 million years ago (a point in time recorded in rocks and referred to by geologists as the K-T boundary). [. . .] However, the supertree shows that the placental mammals had already split into these sub-groups by 93 million years ago, long before the space impact and at a time when dinosaurs still ruled the planet.

Mammal rise 'not linked' to dinos (BBC News)
Mammals Family Tree (1.6MB PDF)


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