New light on evolution
A FOSSIL jawbone, which was discovered in March near Inverloch, about 150 kilometres southeast of Melbourne, Australia, might change all that we know about the evolution of mammals.
The established view is that almost all mammals - including humans - are placentals which originated in the northern hemisphere more than 100 million years ago and spread across the world. The two other groups among mammals - the egg-laying monotremes and the marsupials (in which the young mature in a pouch) - struggled to compete with the fast-paced placentals. Australia is their main remaining stronghold where they are thought to have migrated only five million years ago.
But the new evidence suggests that placentals arose simultaneously in both the southern and the northern hemispheres. Nicola Barton, a volunteer from London working on a site organised by Tom Rich of the Museum of Victoria in Melbourne and his wife, Pat Vickers-Rich of the Monash University, Melbourne, claim that the fossil is 115 million years old and comes from a shrew- like placental. But nothing of this sort was supposed to have existed in Australia until five million years ago.
Ausktribosphenos nyktos (A nyktos), as has been named by Rich, Vickers-Rich and their colleagues believe that it was an insectivore that lived on the landmass of Gondwana. They are said to have split up into Australia, South America, southern Africa and Antarctica. Its home then lay at an latitude of about 70
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