Many Birds and Mammals 50% Older Than We Thought
Abstract from Nature
30th May 1996
The conventional thought has been, for some years, that the major different orders of birds and mammals came into being about 65 million years ago as a result of the Cretaceous/Tertiary extinction event. This caused the dinosaurs to become extinct and allowed a flowering of bird and mammal diversity.
However writing in Nature (381, 226-229) S. Blair Hedges, Patrick Parker, Charles Sibley and Sudhir Kumar provide compelling evidence that the rapid differentiation of bird and mammal orders happened 30 million years earlier. This was when the movement of the tectonic plates was going through a period leading to the break-up of continents so isolating the ancestor animals.
There is little fossil evidence from this period and most modern orders are first represented by fossils from 55-65 million years ago. This compares with the very first birds from 150 million and mammals from 220 million years ago. But this is not the only way to find out when animals diverged. They decided to investigate the genetic material of the existing members of different orders of birds and mammals. There are genes which show a constant rate of substitution and so by looking at these they were able to estimate when the orders diverged. The average of the times they estimated were at least 50% and up to 90% earlier than had previously been thought. Tests were carried out on a number of different orders of birds: chicken, duck, rhea, parrot, cuckoo, dove and stork.