A 225-million-year-old mammal is the oldest ever identified

Brasilodon quadrangularis was a small shrew-like creature, about 20 centimeters (8 inches) long, that roamed the Earth 225 million years ago simultaneously with some of the oldest dinosaurs and sheds light on the evolution of modern mammals, according to a team of Brazilian and British scientists.

The discovery was made by researchers from the Natural History Museum in London, King’s College London and the Federal University of Rio Grande do Sul in Porto Alegre.

Scientists relied on evidence from fossils of hard tissues such as bones and teeth. This is because the glands of mammals, which produce milk, have not been preserved in fossils found so far.

Until now, the Morganucodon was considered the first mammal, with isolated teeth showing that it was about 205 million years old. The Morganucodon had a small gerbil-like body and a long face that resembled that of shrews or civets.

The dental data in the study, published Tuesday in the Journal of Anatomy, dates Brasilodon quadrangularis to 225 million years ago — 25 million years after the Permian-Triassic mass extinction event — the third and largest mass extinction event, when more than 90% of the mass extinction occurred. species in the ocean disappeared and 70% of terrestrial animals became extinct.

Wrong identity

Martha Richter, a research associate at the museum and senior author of the paper, told CNN that the Brasilodon quadrangularis was previously considered an “advanced reptile,” but examination of its teeth “conclusively” showed it to be a mammal.

“If you think about reptiles, they have a lot of different replacement teeth throughout their lives, but we mammals only have two. First the baby teeth and then the second dentition that replaces the original set. This is what defines mammals,” Richter said. .

Brasilodon is the oldest extinct vertebrate with two sequential sets of teeth — deciduous teeth and one permanent set — also known as a diphyodontia, the press release said.

The first set starts developing during the embryonic stage and the second set develops after birth.

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Richter and her colleagues examined three mandibles of the species, which lived in what is now the southernmost part of Brazil. Under the microscope, they discovered “the type of replacement teeth found only in mammals,” she said.

Richter added: “This was a very, very small mammal that was probably a burrowing animal that lived in the shadow of the oldest dinosaurs known from that period.”

She said the team had been working on the project for more than five years and described their discovery as “very important.”

In the press release, Richter said the findings have contributed “to our understanding of the ecological landscape of this period and the evolution of modern mammals.”

Moya Meredith Smith, contributing author and professor of evolutionary dentoskeletal biology at King’s College London, said in the release: “Our paper raises the level of debate about what defines a mammal and shows that it was a much earlier time of origin in the fossil record than previously known.”

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