New “super-tree” theory
Hot on the heels of a recent post where I talked about dominant narratives, comes the news that the March 29 2007 issue of the journal, Nature, carries an article questioning the long-cherished view that the dinosaur mass extinction paved the way for the ancestor’s of today’s mammals to thrive.
Every school child is taught that the dinosaurs ruled for hundreds of millions of years until a large rock aka asteroid smashed into the Yucatan Peninsula and wiped our giant friends off the face of the Earth some 65 million years ago. The void left by Dino the dinosaur, we were told, was filled by the immediate diversification of species. This has been the grand narrative up to now.
But an international team of scientists has constructed a complete evolutionary tree for mammals – a super-tree – that places the rapid species diversification well after the dinosaur disappearance. In fact, there was a 10 to 15 million year gap!
Scientists can estimate the time species diverged from their common ancestor by counting the number of mutations. Talk about a complex web of relationships – scientists have been exploring the evolutionary relationships among all extant mammal species over the past 160 million years. 4,500 extant mammals’ DNA was matched against fossil records to create a “super tree”. What they found was that although there was a small spike of mammalian diversification immediately after the dinosaur die-off, most of those species, however, died out without leaving descendants today. Diversification didn’t really take off until the Eocene epoch, about 56 to 34 million years ago. What took the ancestors of today’s mammals so long to diversify? the jury is still out on this one, but what is really exciting is that scientists are using the new super-tree to determine how evolutionarily unique a species is.
The endangered red panda of northern India and southern China is 39 million years removed from its closest relative, for example, which may mean it is more worthwhile to save this species than one that only diverged 1 or 2 millions years ago.