The oldest mammal on Earth is identified in Rio Grande do Sul

A tiny animal measuring 20 cm in length, similar to a mouse, with a skull smaller than 4 cm and teeth measuring about 2 mm, which roamed the central region of Rio Grande do Sul, is today considered the oldest mammal on the planet.

The discovery was made by researchers from UFRGS (Federal University of Rio Grande do Sul), based on microscopic analysis of the jaws and teeth of fossils found in Faxinal do Soturno, about 50 km from Santa Maria (RS).

The city is one of the 22 municipalities in the state of Rio Grande do Sul located in the area of ​​occurrence of the so-called Santa Maria Formation, a geological unit known worldwide for over a century for the presence of vertebrate fossils.

In the case of fossil “mice”, it is believed that these animals, scientifically named Brasilodon quadrangularislived between 225 and 220 million years ago, at the end of the Triassic period (which lasted from 250 to 200 million years).

Conducted together with two English researchers from King’s College and the Natural History Museum in London, the research was published last Tuesday (6) in the English journal Journal of Anatomy.

In fact, the fossils were found in 2003, when Brasilodon has been described in the international literature. At that time, however, he was not yet considered a mammal.

But how is it possible to know if a fossil was from an animal that suckled or not?

Brasilodon was not considered a mammal because the criterion used by paleontologists to make this determination did not take into account whether the animal fed on milk or not — even because it had never been possible to demonstrate this in a fossil — but the presence of the three tiny bones, that transmit the sound to our ear (the hammer, the anvil and the stirrup), which were not yet differentiated in the gaucho fossil.

Dentist Sergio Cabreira, born in Faxinal do Soturno, decided, in 2004, to study the teeth of this animal in his doctoral project, in the Graduate Program in Geosciences at UFRGS.

Cabreira analyzed a set of three jaws from specimens of Brasilodon of different sizes, therefore, in different stages of growth, to determine how the development of the dentition of that animal took place.

The images obtained by him under a microscope showed that Brasilodon had only one tooth replacement, with “baby” teeth that were later replaced by permanent teeth.

This feature, called diphodontia, is exclusively present in mammals, which indicates that they already inhabited the planet more than 20 million years earlier than previously thought.

A dentist by training, paleontologist Sergio Cabreira, 65, says the discovery is a paradigm shift. “Because it’s the first purely biological analysis that has done a scrutiny of this bone-dental framework of the jaws of these animals,” he says.

In his assessment, biological life does not fit within a mathematical algorithm.

“It is more complex to classify living beings”, he says. “The academic world never imagined that it would be possible to do this type of work this way. We created a new direct and objective method that, unlike cladistics, is fully verifiable and falsifiable. In other words, our method is pure science.”

For geologist and paleontologist Cesar Schultz, 61, professor at UFRGS, advisor to Cabreira and who also signs the work, the great novelty in this discovery is that “we are bringing evidence that there already existed animals with a typically mammalian dentition (and needed to feed milk to produce them), long before the development of the three ear bones, which changes the way of interpreting fossil mammals”.

According to Schultz, the discovery is a milestone, because this same method, based on dentition, should be extended to other fossils, which could reveal even older mammals in the world.