Brasilodon quadrangularis is a mouse of about 20 centimeters that lived 225 million years ago and has turned out to be the oldest known extinct vertebrate.
It was listed as a reptile
Paleontologists from London’s King’s College Natural History Museum in London and the Federal University of Rio Grande do Sul in Porto Alegre have examined the fossilized lower jaws of Brasilodon quadrangularis , a mouse-sized creature that lived in Brazil during the time from the Late Triassic. Analysis of the different growth stages showing tooth development in each of the Brasilodon fossils provided evidence that these were the remains of a mammal . The two sets of teeth came from a small “shrew-like” animal that was around 20 cm long.
Previously, the geological time of mammals had been dated at 205 million years. This rediscovery advances it by two tens of millions of years. A prehistoric mouse marking a much earlier origin of mammals.
Thus, dental records date to 225 million years ago, 25 million years after the Permian-Triassic mass extinction that led to the extinction of approximately 70 percent of the terrestrial vertebrate families.
What animal was considered the first mammal?
Previously, a tiny animal called Morganucodon was considered the first mammal, but its oldest fossils, represented only by isolated teeth, date from about 205 million years ago.
Regarding the remains of Brasilodon , a key feature of mammals known as diphyodontia is clear : “the first set begins to develop during the embryonic stage and a second and final set of teeth develops once the animal is born,” explained the researchers. researchers in their study published in the Journal of Anatomy. “By contrast, reptile dentitions are different, especially because the replacement is ‘many-for-one’ (polyphodonty), in which each tooth has regeneration of teeth many times during a reptile’s life to replace damaged ones.”
Diphyodontia is a complex and unique phenomenon that, together with tooth replacement , involves profound and time-controlled changes in the anatomy of the skull, for example, the closure of the secondary palate (the roof of the mouth) that allows the youngsters suck while breathing through their mouths at the same time. It has also been shown to be related to endothermy and even fur.
” At 225.42 million years old , this is the oldest known mammal in the fossil record contributing to our understanding of the ecological landscape of this period and the evolution of modern mammals. The evidence for how the dentition was built during development time is crucial and definitive in proving that brasilodons were mammals,” adds Professor Moya Meredith Smith, a researcher at King’s College London. “Our paper raises the level of the debate about what defines a mammal and shows that it was a much earlier time of origin in the fossil record than previously known.”
Brasilodon quadrangularis existed at the same time as the oldest known dinosaurs and probably lived in burrows like the shrews we see today.
Referencia: Sergio F. Cabreira et al. Diphyodont tooth replacement of Brasilodon – A Late Triassic eucynodont that challenges the time of origin of mammals. Journal of Anatomy, published online September 5, 2022; doi: 10.1111/joa.13756
