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Two Discoveries changing science's Mind

tiny insect eating mammal Image from "POPSCI" at Item from "The Independent" an English broadsheet

"Mammal the size of a paperclip offers key to evolution"

By Steve Connor Science Editor 25 May 2001

"A tiny animal no bigger than a paperclip which scurried around during the time of the dinosaurs has been found to hold the key to the evolution of warm-blooded mammals.

The furry creature which lived 195 million years ago has been identified by scientists as having the simple one-boned jaw and three middle-ear bones that distinguishes the mammals ­ including man ­ from other animals.

It means that one of the anatomical hallmarks of mammals had evolved about 40 million years earlier than previously thought, raising the intriguing prospect that without it the large brains of mammals, especially those of humans, might not have evolved.

A team of Chinese and American scientists discovered the animal's skull, which is less than half an inch long, in the remarkable fossil beds of Yunnan province in China, which have revealed a wealth of information about prehistoric life.

Unlike the skulls of reptiles, the skull possesses the mammalian signature of three middle ear bones which have "floated off" from the lower jaw bone. In addition to improved hearing, the animal would also have had better control over chewing the small insects it probably lived on.

The scientists, who report their find today in the journal Science, have named the creature Hadrocodium wui, which means "full head" because of its third distinguishing feature ­ a relatively large brain case.

They believe that an enlarged brain, leading to improved intelligence, went hand in hand with the separating of the lower jaw bones into the three small bones that amplify sounds in the mammalian middle ear.

When the dinosaurs became extinct about 65 million years ago, the small, shrew-like mammals that were alive at the time eventually evolved into the larger, warm-blooded animals that came to dominate the Earth in the age of the mammals.

Hadrocodium's distinguishing features show that the anatomical features that helped to make this happen were actually well formed many tens of millions years before this crucial turning point in the history of life.

"It appears that some of the changes in the jaw and ear of mammals were completed before the appearance of Hadrocodium, and that Hadrocodium represents the final step in the separation between the middle ear and the mandible," Dr Luo said.

Scans of the animal's skull also show that the bigger braincase was particularly enlarged in specific areas, such as the olfactory bulbs involved in the sense of smell.

Despite its puny size, Hadrocodium had all the primitive attributes that would enable the mammals to gain the intelligence and ability to survive the extinction of the dinosaurs in their rise to become the most dominant large animals on Earth."


`Jurassic beaver' found in China

The discovery of a fossil beaver that lived when the dinosaurs ruled the Earth could challenge some currently accepted ideas on mammal evolution.

Castorocauda lutrasimilis, which was unearthed in China, is a species previously unknown to science.

Image courtesy of Mark A Klinger/CMNH.
Jurassic Beaver
"Jurassic Beaver"

It dates back to 164 million years ago, a time when mammals were thought to be primitive creatures confined to land.

But this animal was adapted to life in water, meaning scientists may now have to rethink their theories.

The fossil was found in the Middle Jurassic Jiulongshan Formation, a deposit rich in the remains of dinosaurs, early insects and other organisms.

Like modern beavers, the creature had fur, a broad scaly tail, and webbed feet for swimming. It was about the size of a small female platypus and had seal-like teeth for eating fish.

Aquatic mammal

Such advanced features have surprised many scientists, suggesting mammals that lived during the hey-day of the dinosaurs had already conquered a variety of environments.

The mammals of the time were once thought to be largely primitive shrew-like creatures, scuttling at the feet of dinosaurs, and only flourishing when the dinosaurs died out some 65 million years ago.

Commenting on the find, revealed in the journal Science, Thomas Martin of the Forschungsinstitut Senckenberg in Frankfurt, Germany, said it showed mammals had conquered the water 100 million years earlier than previously thought.

"This exciting fossil is a further jigsaw-puzzle piece in a series of recent discoveries, demonstrating that the diversity and early evolutionary history of mammals were much more complex than perceived less than a decade ago," he wrote.

Last Updated: Friday, 24 February 2006, 21:35 GMT

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