Brasilodon quadrangularis was a small shrew-like creature, about 20 cm (8 in) long, that walked the Earth 225 million years ago It coincides 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 provided by fossils of hard tissues such as bones and teeth. This is because the glands of mammals, which produce milk, have not been preserved in any fossils found so far.
So far, Morganucodon has been considered the first mammal, with isolated teeth showing that it dates back to about 205 million years ago. Morganucodon had a small jerboa-like body and a long face similar to that of a shrew or civet.
Martha Richter, a science fellow at the museum and lead author of the paper, told CNN that Brazil was previously thought to be an “advanced reptile,” but an examination of its teeth shows “conclusively” that it was a mammal.
“If you think of reptiles, they have many, many replacement teeth throughout their lives, but we mammals have only two. First, the deciduous teeth, then the second teeth that replace the original set. That’s what distinguishes mammals,” Richter said. .
The press release said prazilodon is the oldest extinct vertebrate with two consecutive sets of teeth – deciduous teeth and one permanent set – also known as a diphyodonty.
The first group begins to develop during the embryonic stage and the second group develops after birth.
Richter and her colleagues examined three lower jaws of species that lived in the area covered today in southern Brazil. Under a microscope, she said, they discovered “the type of replacement tooth found only in mammals.”
“This was a very, very small mammal that was probably a burrowing animal living in the shadows of the oldest dinosaurs we know from that period,” Richter added.
She said the team had been working on the project for more than five years and described their discovery as “extremely significant”.
In the press release, Richter said the findings 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 structural biology of evolutionary teeth at Kings College London, said in the statement: “Our paper raises the level of controversy about what defines mammals and shows that it was a much earlier time of origin in the fossil record than previously known.”