The world’s oldest known mammal has been identified using dental records – predating what scientists previously thought was the first mammal to walk the Earth by millions of years – according to new research.
In the study, published in the peer-reviewed Journal of Anatomy on MondayBrazilian and British researchers from the Federal University of Rio Grande do Sul, London’s Natural History Museum and King’s College London confirmed that the Brasilodon quadrangularis was the earliest mammal with fossil records of the animal’s teeth sets.
The Brasilodon was a tiny, “shrew-like” animal that measured almost 8 inches long. Dental records for the mammal date back more than 225 million years – meaning the Barsilodon existed at the same time as some of the oldest dinosaurs, but 25 million years after the Permian-Triassic mass extinction, according to a Natural History Museum news release.
“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,” Martha Richter, scientific associate at the museum and senior author of the paper, stated in the release.
Before the discovery about the Brasilodon’s age, scientists had previously confirmed that the Morganucodon, another small, rodent-like creature, was the world’s earliest mammal.
The Morganucodon’s oldest fossils, which are isolated teeth, date back 205 million years. So, the Brasilodon is believed to be roughly 20 million years older.
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To date, mammalian glands (such as those that produce milk) have not been persevered in any recovered fossils. Scientists have to turn to “hard tissues,” such as bones and teeth that fossilized, “for alternative clues,” the Natural History Museum notes.
The Brasilodon was identified as a mammal because of its two sets of successive teeth. When analyzing three lower jaws of different growth stages in particular, the researchers concluded that the Brasilodon’s first set of teeth (which started developing before birth) were later replaced with an “adult set.”
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Two sets of teeth characterize mammals, the researchers note. In contrast, reptiles, for example, see teeth replaced many times throughout their lives.
“The evidence from how the dentition was built over developmental time is crucial and definitive to show that Brasilodons were mammals,” Moya Meredith Smith, contributing author and professor at King’s College London stated. “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.”