Oldest mammal discovered

[Prehistory Resurrection]

- Research has shown that the oldest mammal is a mouse-sized creature, named Brasilodon quadrangularis (Greek for "Brazil tooth).

Brasilodon quadrangularis was a shrew-like mammal but mouse-sized.  It was approximately 12 cm (8 inches long) and weighed about 20 grams. It lived about 225 million years ago in Brazil, during the Norian stage of the Late Tirassic Period; the same time as the earliest dinosaurs. It probably lived in burrows like modern-day shrews. Image credit: Anatomical Society/Wiley.

-The earliest mammal was once thought to be Morganucodon, dating from about 205 million years ago, but the study of the fossilized lower jaw of Brasilodon has proved that the record in geological time for mammals is now 225 million years ago.

Morganucodon, also an early mammal living alongside early dinosaurs during the Late Tirassic Period.

- The dental records date 225 million years ago, 25 million years after the Permian-Triassic mass extinction event that led to the extinction of roughly 70% of terrestrial vertebrate families.

-Examining the dentitions of Brasilodon quadrangularis, Dr. Martha Richter from the Natural History Museum, London, and colleagues discovered evidence of only one set of replacement teeth — a key feature of mammals known as diphyodonty. Diphyodonty is a complex and unique phenomenon that, with tooth replacement, also 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 at the same time.

-"The first set starts developing during the embryonic stage and a second and last set of teeth develops once the animal is born," the researchers explained.

-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."

-"The evidence from how the dentition was built over developmental time is crucial and definitive to show that brasilodons were mammals," added Professor Moya Meredith Smith, a researcher at King's College London.

. It was once thought to be a cynodont; a group of mammal-like reptiles that lived from the Early Permian and Late Triassic Periods, with well-developed, specialized teeth. But research has now shown that Brasilodon was a definitive mammal.

-"Our paper raises the level of debate about what defines a mammal and shows that it was a much earlier time of origin in the fossil record than previously known."