|A rock sample from the K-T boundary. The white band|
is an iridium rich layer deposited by the meteorite
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.