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Earth's first mammals lived far longer than their modern counterparts

October 12, 2020. Summarized by summa-bot.

Earth's earliest mammals spent their lives at a more leisurely pace than their modern counterparts, but they lived a lot longer, analysis of some 200-million-year-old teeth has shown.

(CNN)Earth's earliest mammals spent their lives at a more leisurely pace than their modern counterparts, but they lived a lot longer, analysis of some 200-million-year-old teeth has shown.

Using X-ray technology, palaeontologists studied the fossilized teeth of some of Earth's earliest mammals, Morganucodon and Kuehneotherium, shrew-sized insectivores that walked the earth alongside early dinosaurs during the Early Jurassic marine transgression, in what is now Glamorgan in South Wales.

Experts from the UK's University of Bristol and Finland's University of Helsinki studied growth rings in the mammals' tooth sockets, discovering the animals lived for up to 14 years -- surprising, given similarly sized modern-day animals, such as mice and shrews, have a lifespan of between one and two years in the wild.

I was dumbfounded as these lifespans were much longer than the one to three years we anticipated for tiny mammals of the same size," Dr Elis Newham, Research Associate at the University of Bristol, said in a statement.

They had specialized chewing teeth, relatively large brains and probably had hair, but their long lifespan shows they were living life at more of a reptilian pace than a mammalian one," Newham said.

"There is good evidence that the ancestors of mammals began to become increasingly warm-blooded from the Late Permian, more than 270 million years ago, but, even 70 million years later, our ancestors were still functioning more like modern reptiles than mammals," he added.

Still, while the mammals had a reptilian pace of life, experts found evidence of sustained exercise in the bone tissue -- which contained blood vessels and fat -- of the early mammals.

"We found that in the thigh bones of Morganucodon, the blood vessels had flow rates a little higher than in lizards of the same size, but much lower than in modern mammals.

This suggests these early mammals were active for longer than small reptiles but could not live the energetic lifestyles of living mammals," Newham added.

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