Jurassic pipsqueak

Ancestor of modern mammals discovered

Source: Jeff Hecht
New Scientist June 2 2001 p18

A skull 13mm long from a shrew-like mammal, discovered in Yunnan province, China, is estimated to be 195 million years old, when dinosaurs were still alive. Zhexi Luo, from Carnegie Museum of Natural History, Pittsburgh, calculates that this mammal, called the Hadrocodium, weighed two grams. The skull is smaller than any discovered so far from this period, and differs from the skulls of contemporary mammal relatives in having a relatively large brain case, as is found in modern mammals. Modern mammals also have a middle ear made from bones that are part of the jaw in reptiles, and this new skull appears to have had a middle ear similar to that of modern mammals, unlike other mammal relatives living at that time. Harvard University’s Alfred Crompton, a palaeontologist, believes that the change in bone structure occurred as mammal ancestors’ skulls became smaller. This may have helped mammals develop sharp hearing. Mammals living during the age of dinosaurs probably had to be nocturnal to survive.