The oldest mammal identified was initially thought to be the 205-million-year-old Morganucodon. But a new discovery pushes beyond this date, with another species.
You have things in common with Brasilodon quadrangularis, although this animal has long been extinct. Because humanity belongs to mammals, just like this species. This 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 6 September 2022. The study of its fossils was also published in the magazine Anatomy diary.
Brasilodon quadrangularis it looked like a shrew. It measured about 20 centimeters and inhabited the Earth 225 million years ago. This dating shows that it is even older than the Morganucodon, previously considered the most distant mammal. But the oldest known fossil of the latter dates back to 205 million years ago. The difference is significant.
The mammal has been dated thanks to its teeth
When such a period of time has elapsed, there is nothing “soft” left in the body, and therefore even fewer mammary glands to identify: these glands are a feature of all male and female mammals. The paleontologists must then mobilize the bones or the teeth: in other words, all the “hard” tissues that over the centuries have turned into limestone. This is what is used for dating, but also to determine what type of species.
In this case, the scientists discovered that this animal was diiodon: it had a set 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 that regenerate new teeth multiple times during their lifetime, “many for one” replacements, also known as polyphiodontics. “
However, the level of evidence seems sufficient to conclude that the Brasilodon is currently the oldest mammal to be listed. ” Our study reignites the debate over what defines a mammal and shows that this is an original period much earlier in the fossil record than previously known. Observes Moya Meredith Smith, lead author of the article.