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.
(...) 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.
(...) “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.”
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