The first mammals were like reptiles in terms of metabolic rate

The first mammals appeared at the end of the Triassic period, 220-210 million years ago. Outwardly they resembled

small shrews and weighed only 4-5 grams.

In the past, scientists believed that key featuresmammals, including their warm-blooded nature, arose at approximately the same time. We found that despite their complex brains and advanced behaviors, these animals lived long, leisurely lives like reptiles, rather than fast, short lives like modern mammals. 

Alice Newham, one of the authors of the work, is a paleontologist from the University of Bristol in the UK.

Paleontologists from the University of Bristol inGreat Britain and the University of Helsinki in Finland first studied the tiny, pinhead-sized teeth of two of the earliest mammals, Morganucodon and Kuehneotherium, who lived in modern South Wales 200 million years ago, in the Early Jurassic, using powerful synchrotron X-rays.

The structure of the oldest teeth known to scienceprimitive mammals says that the earliest ancestors of man were small creatures and ate insects and fruits. For a long time, researchers believed that mammals began to "grow" and occupy new ecological niches after the extinction of the dinosaurs. However, recent studies show that this began to happen 20 million years before the fall of the asteroid that destroyed the dinosaurs.

After examining the growth rings of the cement of the roots of the teeth,which are deposited every year, like tree rings of trees, scientists have calculated that morganucodon lived up to 14 years, and cuneotherium - about nine, and not a year or two, as previously thought.

This discovery came as a big surprise.for researchers. In the past, paleontologists believed that warm-bloodedness and the associated high level of activity at any time of the day were one of the most ancient and important features of mammals, thanks to which these animals occupied those ecological niches that cold-blooded reptiles could not claim.

Newham notes that this does not necessarily speak inthe benefit of the fact that morganucodons and cuenotherium were not warm-blooded. But this suggests that the ancient relatives of modern mammals were significantly inferior to them in the level of activity. How and when ancient mammals became more like modern mammals remains to be seen.

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