Found the oldest mammal, the evidence is in the teeth

The oldest mammal in the world is the Brasilodon quadrangularis, a sort of shrew just 20 centimeters large that lived 225 million years ago in the late Triassic, at the time of the first dinosaurs.

This is demonstrated by the study of his fossil teeth, published in the Journal of Anatomy by researchers from the Federal University of Rio Grande do Sul in Porto Alegre (Brazil) in collaboration with the Natural History Museum and King's College of London.

The teeth represent a key find for the study of ancient mammals, because the mammary glands have not been preserved in any known fossil so far.

"Comparative studies with recent mammalian teething suggest it was a placental animal with a rather short lifespan," explains Martha Richter of the Natural History Museum in London.

"Dating back 225.42 million years, 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 Brasilodon is the oldest extinct vertebrate with two dentitions: in embryonic life it developed a set of deciduous teeth, which after birth were replaced by a set of permanent teeth (a condition known as 'diiodontia').

The replacement of the teeth took place with the times and methods typical of mammals and not as in reptiles, which regenerate their teeth several times during their life ('polyphiodontia').

This discovery pushes back the origin of diiodontics by 20 million years and allows the Brasilodon to wrest the oldest mammalian primacy from the Morganucodon, which lived about 205 million years ago.