Sunday, 18 March 2012

New Research Suggests That The Demise Of The Dinosaurs Did Not Aid The Rise Of The Mammals

A rock sample from the K-T boundary. The white band
 is an iridium rich layer deposited by the meteorite
150 million years ago, a collision within the asteroid belt ejected a vast cluster of asteroids from particles as small as a grain of sand to pieces the size of mountains. They traversed the vast wastes of space, heading towards Earth until, 65 million years ago, a single piece approximately 10 kilometres in diameter collided with the Gulf of Mexico. This single collision was responsible for the extinction of the dinosaurs as well as many other groups of animals, including the ammonites.

Many scientists thought that, while the dinosaurs became extinct, the mammals were able to rise, diversify, and after a few million years, become the dominant animal group on the planet. A study of species diversity, however, before and after, in conjunction with the geological timescale, has shown that the death of the dinosaurs had very little impact on mammal success. Researchers at the University of New South Wales believe that mammals had already begun to diversify long before the extinction event.

There have been two distinct spikes in mammalian evolution, one 93 million years ago which brought about the placentals, the marsupials and the monotremes who would have been co-existent with the dinosaurs. The other did not occur until 10 million years after the dinosaur extinction meaning that the destruction of their reptilian predators did not affect their speed of diversification. At this point the Earth had already recovered, also ruling put the possibility that they simply filled in the empty ecological niches left by the K-T meteorite.

'The big question now is what took the ancestors of modern mammals so long to diversify' said study team member Ross MacPhee. 'It's as though they came to the party after the dinosaurs left, but just hung around while all their distant relatives were having a good time.' The researchers believe that the answer to this question is linked to the way the climate fluctuated before and after the K-T extinction event and the emergence of flowering plants.