Skull scans on two of the oldest known mammal species have shown their brains were large and well-developed in areas that promote a strong sense of smell, scientists said on Thursday.

Researchers believe the mammalian brain evolved in three stages -- first the boost in sense of smell, then the ability to touch and feel through body hair, and finally the brain coordination to produce "skilled muscle movement."

They focused on two shrew-like animals -- the Morganuocodon and the Hadrocodium -- plucked from the Jurassic fossil beds of China for the study published in the journal Science.

Using X-ray computed topography, or three-dimensional CT scans, to reconstruct the interior of the skull, researchers were able to see what the brains of these little paper-clip sized creatures may have been like.

The nasal cavity and related smell regions were enlarged, as were parts of the brain that process olfactory cues, indicating an acute sense of smell.

The critters also used their fur as a sensor to feel their way around and avoid harm, according to lead study author Tim Rowe, director of the vertebrate paleontology laboratory at the University of Texas at Austin.

"Now we have a much better idea of the historical sequence of events and of the relative importance of the different sensory systems in the early evolution of mammals," said Rowe.

"It paints a much more vivid picture of what the ancestral mammal was like and how it behaved, and of our own ancestry."

The latest findings are a boon to scientists who have long wondered what went on inside the skulls of ancient creatures but dared not destroy the old, rare fossil artifacts in order to find out.

"I have spent years studying these fossils, but until they were scanned it was impossible to see the internal details," said Zhe-Xi Luo, a curator at the Carnegie Museum of Natural History.

"I was absolutely thrilled to see what the brains of our 190-million-year-old relatives were like."

The entire project covered a dozen early fossil mammals and more than 200 living species over the past decade. A library of the scan results is available at www.digimorph.org.