by David Catchpoole

Published: 21 November 2006 (GMT+10)

The amazingly complex middle ear of mammals has three bones—the incus, malleus and stapes, popularly known as the hammer, anvil and stirrup—while reptiles have only one. Because of its complexity, evolutionary theorists have long said it must have originated once only, in some ancestral creature from which all mammals today are descended. As an article in New Scientist put it: ‘The process was so complex that mammal experts assumed that it must have occurred only once, before monotremes split off from the other mammals more than 150 million years ago.’1

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