Ancient tiny teeth reveal first mammals lived more like reptiles — ScienceDaily

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Pioneering analysis of 200 million-year-old teeth belonging to the earliest mammals suggests they functioned like their cold-blooded counterparts — reptiles, leading less active but much longer lives.

The research, led by the University of Bristol, UK and University of Helsinki, Finland, published today in Nature Communications, is the first time palaeontologists have been able to study the physiologies of early fossil mammals directly, and turns on its head what was previously believed about our earliest ancestors.

Fossils of teeth, the size of a pinhead, from two of the earliest mammals, Morganucodon and Kuehneotherium, were scanned for the first time using powerful X-rays, shedding new light on the lifespan and evolution of these small mammals, which roamed the earth alongside early dinosaurs and were believed to be warm-blooded by many scientists. This allowed the team to study growth rings in their tooth sockets, deposited every year like tree rings, which could be counted to tell us how long these animals lived. The results indicated a maximum lifespan of up to 14 years — much older than their similarly sized furry successors such as mice and shrews, which tend to only survive a year or two in the wild.

“We made some amazing and very surprising discoveries. It was thought the key characteristics of mammals, including their warm-bloodedness, evolved at around the same time,” said lead author Dr Elis Newham, Research Associate at the University of Bristol, and previously PhD student at the University of Southampton during the time when this study was conducted.

“By contrast, our findings clearly show that, although they had bigger brains and more advanced behaviour, they didn’t live fast and die young but led a slower-paced, longer life akin to those of small reptiles, like lizards.”

Using advanced imaging technology in this way was the brainchild