The discovery of the oldest known mammal puts their origin back 20 million years!

By analyzing the dental remains of a small animal named Brasilodon quadrangularis, researchers have discovered that the latter was in fact a mammal! It then becomes the oldest known mammal, whose origin dates back 225 million years.

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In a new study published in Journal of Anatomyof the paleontologists looked at the lower jaws of a small animal that lived 225 million years ago: the Brasilodon quadrangularis. Discovered in Brazil in 2003, it was similar in appearance and size to a shrewand populated the Earth about 225 million years ago.

But its particularity lies in its dentition: the three jaws, studied at different stages of growth, show that the Brasilodons had a diphyodont dentition, that is to say, which is replaced only once during their life.

A characteristic specific to mammals, and which would push back the origin of this class of vertebrates of 20 million years, i.e. only 25 million years after the great Permian-Triassic extinction. Indeed, until today, the oldest known mammal was the Morganucodonanother small mammal about ten centimeters long, appeared at the end of the Triassic 205 million years ago.

The debate on the origin of mammals is revived

But diphyodontia alone is not enough to prove that the Brasilodons were indeed mammals. Indeed, to ensure that the animal studied corresponds to a mammalit would also be necessary to show that the first dentition is linked to the lactation. A fact impossible to verify, but which is not necessary according to Moya Meredith Smith, co-author of the study and professor emeritus of evolution and development of theanatomy dentoskeletal King’s College from London.

“Evidence of how the dentition was constructed over developmental time is crucial and definitive in showing that the Brasilodons were mammals. Our article raises the level of debate on what defines a mammal and shows that their time of origin established according to fossils is much older than previously thought. »

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