An international collaboration between scientists and researchers has lead to the discovery of Earth’s earliest known mammal — the 225 million-year-old Brasilodon quadrangularis.

Using fossil tooth and bone records, researchers with the Natural History Museum in London, King’s College London and the Federal University of Rio Grande do Sul in Porto Alegre say the mammal was a small shrew-like creature around 8 inches long with two sets of teeth and walked among some of the oldest dinosaurs.

Illustration of the Brasilodon quadrangularis, the earliest known extinct mammal.

2022 Anatomical Society/Wiley

“Comparative studies with recent mammal dentitions and tooth replacement modes suggest that this was a placental, relatively short-lived animal,” Dr. Martha Richter, a scientific associate at the museum and senior author on the paper, said in a news release. “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.”

According to a team of Brazilian and British scientists, the dental records date back 225 million years, to 25 million years after the Permian-Triassic mass extinction event that led to the extinction of roughly 70% of terrestrial vertebrate families.

They say the Brasilodon quadrangularis predates the previously confirmed first mammal, the Morganucodon, by approximately 20 million years.

“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,” says Moya Meredith Smith, contributing author and emeritus professor of evolution and development of dentoskeletal anatomy at King’s College London.