Oldest Mammal From 225 Million Years Ago Previously Identified as Advanced Reptile

Recent research reveals that the mammal from 225M years ago, previously thought to be an advanced reptile, was a mammal.

In a recent discovery that scientists have hailed as "very significant," the world's oldest mammal has been distinguished using fossil dental records. This animal predates the previously confirmed oldest mammal by about 20 million years.

A team of Brazilian and British scientists discovered the remains of Brasilodon quadrangularis, a small, shrew-like animal that lived 225M years ago and gives a clearer view of the evolution of modern mammals. It was about 20 centimeters (8 inches) long.

Researchers from the Federal University of Rio Grande do Sul in Porto Alegre, King's College London, and the Natural History Museum in London made the discovery.

Hard tissue fossils, like those of bones and teeth, provide scientists with hints about the past. This is because no fossils have yet been discovered that contain milk-producing mammalian glands.

Since isolated teeth from the Morganucodon indicate that it existed around 205 million years ago, it was previously thought to be the earliest mammal. The Morganucodon had a small, gerbil-like body and a shrew-like or civet-like, long face.

According to dental records used in the study, Brasilodon quadrangularis lived 225 million years ago, or 25 million years following the Permian-Triassic mass extinction event, the third and largest mass extinction event, during which more than 90% of marine species vanished and 70% of land animals perished.

Mistaken identity

According to the senior author of the study, Martha Richter, the Brasilodon quadrangularis was once thought to be an "advanced reptile," but an examination of its teeth "definitively" proves that it was a mammal. Richter is also a scientific associate at the museum.

Richter said that Reptiles have a huge variety of replacement teeth throughout their lives, whereas mammals only have two. The milk teeth come first, followed by the second dentition, which takes the place of the first set. Mammals are characterized by this.

According to a news release, Brasilodon, also known as a diphyodonty, is the oldest extinct vertebrate that has two successive sets of teeth: baby teeth and one permanent set.

While the second set emerges after birth, the first set begins during the embryonic stage.

The species lived in the area that is now occupied by the southernmost region of Brazil, and Richter and her team members examined three of the species' lower jaws.

She said that they found the particular replacement teeth which are unique to mammals under a microscope.

Richter added that this extremely tiny mammal was probably a burrowing creature that lived in the shadows of the earliest dinosaurs ever discovered.

The team said their discovery was very important and that they had been working on it for more than five years.

According to Richter's news release, the discoveries improved our knowledge of this period's ecological environment and the development of modern mammals.

According to the press release from Moya Meredith Smith, a co-author of the study, their paper raises the level of discussion surrounding what constitutes a mammal and demonstrates that mammals evolved much earlier in time than previously thought. Smith is also a professor of evolutionary dentoskeletal biology from King's College London, CNN reports.