Dr. Martha Richter, Scientific Associate at the Museum and senior author of the paper, said: “Comparative studies with recent mammal dentitions and tooth replacement modes suggest that this was a placental, relatively short-lived animal. Dated 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.”
Scientists relied on clues from fossils of hard tissues such as bones and teeth because mammalian glands have not been preserved in any fossils found. Until this discovery, the Morganucodon had been considered the first mammal dating back around 205 million years.
On the other hand, Brasilodon is the oldest extinct vertebrate with two successive sets of teeth, including only one set of replacements, also known as a diphyodonty. This differs from that of reptiles who regenerate new teeth multiple times during their lives, the ‘many for one’ replacement also known as poliphyodonty.
Diphyodonty involves profound, time-controlled changes to the skull anatomy, for instance, the closure of the secondary palate (the roof of the mouth) that allows the young to suckle while breathing simultaneously. It has also been shown to be linked to endothermy and even placentation (live birth) and fur.