According to a press release from the Natural History Museum, the fossil dental records of Brasilodon quadrangularis, the oldest mammal ever discovered. The two sets of teeth are from a small ‘shrew-like’ animal about 20cm in length.
225 million years ago
The dental records are from the Late Triassic/Norian period, which is 225 million years ago. This is 25 million years after the Permian-Triassic mass extinction event, which caused the extinction of about 70% of the terrestrial vertebrate families. The discovery was made by scientists from the Federal University of Rio Grande do Sul in Porto Alegre and the Natural History Museum in London, King’s College.
According to senior author and Scientific Associate at the Museum Dr. Martha Richter, “Comparative studies with recent mammal dentitions & tooth replacement modes suggest that this was a placental, relatively short lived animal. This is the oldest known mammal in the fossil record, dating back 225.42 million years, and it helps us understand the ecological landscape of this time period as well as the evolution of modern mammals.”
Since mammalian glands have not been preserved in any fossils, scientists have relied on information from hard tissues preserved in the fossil, such as bones and teeth. The Morganucodon had been thought to be the earliest mammal, dating from about 205 million years ago, until this discovery.
On the other hand, Brasilodon, also known as a diphyodonty, is the oldest extinct vertebrate with two successive sets of teeth, including just one set of replacements. This differs from reptiles, which grow new teeth multiple times throughout their lives, the “many-for-one” replacement also known as polyphodonty.
Diphyodonty involves significant, time-controlled changes to the anatomy of the skull, such as the closure of the secondary palate (the roof of the mouth), which enables the young to suckle while breath-ing at the same time. Additionally, studies have shown to be linked to endothermy & placentation (live birth), and even fur.
The oldest dinosaur known to science, Brasilodon, likely lived in burrows like shrews do today.
“The evidence from how the dentition was built over developmental time is crucial & definitive to show that Brasilodons were mammals,” said Prof Moya Meredith Smith, contributing author and Emeritus Professor of Evolution and Development of Dentoskeletal Anatomy at King’s College London. Our study intensifies the debate over what defines a mammal and demonstrates that the fossil record dates back much further than previously thought.
The most recent findings move the origin of diphyodonty in mammals and Brasilodon back 20 million years.
“This research is a collaboration between Brazilian and British scientists, who gathered their expertise on skull development, dental anatomy, physiology, & histology to interpret the juvenile & adult fossils of the extinct species Brasilodon quadragularis,” Richter said in his conclusion.
The Journal of Anatomy has published a paper titled “Diphyodont tooth replacement of Brasilodon” that challenges the time of origin of mammals. Brasilodon is a Late Triassic eucynodont.