Earth’s First Mammals Moved Much Slower and Had Longer Lives

By studying “growth rings” in 200-million-year-old fossilized teeth, experts have concluded that some of the first mammals to walk the Earth moved much slower than today’s species and lived longer lives. As a matter of fact, they moved at about the same pace as lizards and snakes.

Experts were able to come to this conclusion by analyzing the growth rings on fossilized teeth belonging to two ancient species called Morganucodon and Kuehneotherium that lived in South Wales during the Jurassic period.

Similar to tree rings, there are also growth rings that are present in tooth sockets that showed how long the mammals lived. Dental tissue called cementum covers the root and helps the tooth to stay fixed in the gum in addition to creating a new layer each year that the animal was alive, therefore, allowing researchers to determine the exact age when it would have died. It also revealed other information such as when the mammal would have been pregnant or suffered from an illness.

Experts analyzed tooth samples to determine the exact age of the ancient mammals.

A tooth belonging to the Morganucodon species was sent to Dr. Ian Corfe from the University of Helsinki for analysis and he stated what he found, “To our delight, although the cementum is only a fraction of a millimeter thick, the image from the scan was so clear the rings could literally be counted.” A total of 200 tooth samples were sent to the European Synchrotron Radiation Facility in France and the Swiss Light Source in Switzerland whose experts also performed X-ray testing.

The high-resolution X-rays showed that the Morganucodon lived up to 14 years and the Kuehneotherium for 9 years. Modern day mice and shrews that live in the wild only live as long as one or two years.

The researchers were quite surprised to find this information out about the lifespans as they had just assumed that the ancient mammals only lived up to a few years old at the longest. Dr. Elis Newham, who is a research associate at the University of Bristol, explained this further by stating, “It was thought the key characteristics of mammals, including their warm-bloodedness, evolved at around the same time,” adding, “By contrast, our findings clearly show that, although they had bigger brains and more advanced behavior, they didn’t live fast and die young but led a slower-paced, longer life akin to those of small reptiles, like lizards.”

The Morganucodon and Kuehneotherium species lived much longer lives than a modern mouse.

Both of the Morganucodon and Kuehneotherium species fell into caves and rock holes so their skeletons were very well preserved. “Thanks to the incredible preservation of these tiny fragments, we were able to examine hundreds of individuals of a species, giving greater confidence in the results than might be expected from fossils so old,” Dr. Corfe noted. (A picture of the tooth scan as well as an artist’s impression of the Morganucodon can be seen here.)

Their research was published in Nature Communications and can be read in full here.

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