Earliest Ever Mammal? Tiny Fossil Teeth Discovered in Britain Shed Light on What Could Be Our Oldest Ancestors

The mammal the teeth belonged to might have looked like this. Dr Mark Witton, palaeo-artist, University of Portsmouth

Paleontologists in the United Kingdom have found two tiny fossilized teeth that they believe belong to some of the earliest mammals to walk the Earth, according to a new paper published in the journal Acta Palaeontologica Polonica.

"Quite unexpectedly [undergraduate student Grant Smith] found not one but two quite remarkable teeth of a type never before seen from rocks of this age," co-author Steve Sweetman, a paleontologist at the University of Portsmouth, said in a press release. "I was asked to look at them and give an opinion and even at first glance my jaw dropped!"

The fossils themselves were collected in 2015 along the southern coast of Britain about halfway between London and the western edge of the island. It's known to be a very good area for fossils—it's even nicknamed the Jurassic Coast. So the researchers gathered 120 pounds of sediment from the site and basically sieved it to see what they could find.

That turned up two tiny teeth that are about 145 million years old. Each tooth belongs to a different species, the scientists concluded, which would have lived at the same time as dinosaurs, which didn't die out until about 66 million years ago. They could represent some of the earliest mammals, the long-lost relatives of humans, cats and elephants alike, depending on how scientists evaluate some controversial 160-million-year-old Chinese fossils.

Because of the importance of teeth to an animal's life, the team can even make some educated guesses about how the critters lived. "The teeth are of a highly advanced type that can pierce, cut and crush food," Sweetman said in the statement, adding that one of the two species may have mostly snacked on insects.

The fossil teeth as seen under a microscope. The scale bar is one millimeter, or about 0.04 inches. University of Portsmouth

"They are also very worn, which suggests the animals to which they belonged lived to a good age for their species," Sweetman added. "No mean feat when you're sharing your habitat with predatory dinosaurs!" The team also believes the critters were furry and nocturnal.

The tiny teeth have been sent to the Natural History Museum, where they can continue to be studied. Many of the most intriguing recent discoveries of early mammal fossils have been made in China, so extending the geographical range of specimens is particularly exciting.

Because the paper also serves as the formal identification of the two new species, the scientists also had the opportunity to name the long-dead critters. One they named Durlstodon ensomi and the other Durlstotherium newmani. Both names commemorate Durlston Bay, the region where the teeth were found—but they also acknowledge two locals, one a pub-owner and local amateur fossil collector, who helped the scientists during their visit.