Oldest known mammal is 225 million years old

The oldest identified mammal was originally thought to be the 205 million year old Morganucodon. But a new discovery pushes this date further, with another species.

You have things in common with Brasilodon quadrangularis, even though this animal has long been extinct. Because humanity belongs to mammals, just like this species. This one has just been identified by the Natural History Museum in London as the oldest mammal discovered to date.

This tiny animal existed at the same time as some of the oldest dinosaurs and sheds light on the evolution of modern mammals “, explains the museum in a post published on September 6, 2022. The study of its fossils was also published in the journal Journal of Anatomy.

Here is the Brasilodon. It measured 20 cm in adulthood, 225 million years ago. // Source: Anatomical Society / Wiley

Brasilodon quadrangularis looked like a shrew. It measured around 20 centimeters and inhabited the Earth 225 million years ago. This dating proves that it is even older than the Morganucodon, previously considered the most distant mammal. But the oldest known fossil of the latter dates back 205 million years. The difference is significant.

The mammal was dated thanks to its teeth

When such a period of time has passed, there is nothing ‘soft’ left in the body, and therefore even fewer mammary glands to identify — these glands being a characteristic of all male and female mammals. Paleontologists must then mobilize the bones or the teeth: in other words, all the “hard” tissues that have turned into limestone over the ages. This is what is used for dating, but also to determine what type of species.

In this case, the scientists found that this animal was diphyodont: it had a series of replacement teeth, replacing the initial teeth (what we call milk teeth). ” Tooth replacement occurs in the same temporal and morphological pattern, which is an essential feature of mammals “, explains the museum. ” It differs from that of reptiles which regenerate new teeth several times during their lifetime, ‘many-for-one’ replacement, also known as poliphyodonty. »

The level of evidence seems in any case sufficient to consider that the Brasilodon is currently the oldest mammal that is listed. ” Our study rekindles the debate over what defines a mammal, and shows that this is a much earlier original time in the fossil record than previously known. “, notes Moya Meredith Smith, main author of the paper.

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