Fossilized Teeth Belonging To ‘Our Earliest Ancestors’ Unearthed In Dorset

Two tiny fossilized molars belonging to the oldest known ancestors of most mammals alive today, including humans, emerged from an excavation site in the cliffs of Dorset, southern England. Known as the Jurassic Coast, the area yielded numerous other archeological finds in the past, but none quite like this one.

The fossils come from two previously undiscovered species of eutherians — small, rodent-like, ancient nocturnal mammals that later evolved into placental mammals. This makes eutherians the ancient common ancestor of the entire mammalian lineage that extends from humans and elephants to blue whales and pygmy shrews — with the exception of pouch-carrying marsupials, such as kangaroos, and egg-laying monotremes, such as platypuses.

The discovery, detailed in a study published on November 7 in the journal Acta Palaeontologica Polonica, is credited to Grant Smith, an undergraduate student from University of Portsmouth. Just like most other remarkable discoveries, this one too happened by chance.

The newbie paleontologist came across the two fossilized teeth in the summer of 2015, while doing research for his dissertation project. As he was combing through 130 pounds of ancient Cretaceous rocks collected at the site, hoping to find anything remotely interesting, Smith stumbled upon the discovery of a lifetime.

Study author Dr. Steve Sweetman, who was called in to identify the fossilized teeth, describes the experience as “a jaw-dropping moment.”

According to the university, the two samples are indisputably the oldest eutherian fossils ever found, and the first eutherian remains uncovered in the Jurassic Coast of Dorset. Dr. Sweetman analyzed the fossilized teeth and established they dated back to nearly 145 million years ago, based on the age of the rocks that encased them.

Dr. Sweetman notes the find is “quite remarkable,” considering the two eutherian molars were “of a type never before seen” from early Cretaceous rocks.

“These were the sorts of things you’d expect to see in the Upper Cretaceous, not way down in the base of the Cretaceous,” he said in a statement.

A university news release discussing the discovery argues this unexpected find is at least 20 million years older than the fossils that previously claimed the title of earliest known eutherian remains.

“Our 145 million-year-old teeth are undoubtedly the earliest yet known from the line of mammals that lead to our own species.”

Up until now, the eutherian fossil record dubbed a Chinese fossil called Juramaia as the oldest sample ever recovered. But recent studies inferred this fossil, discovered in 2011 and preceding the Dorset samples by 15 million years, may not be eutherian after all, shows National Geographic.

Dr. Sweetman is certain the two molars recovered from the cliffs of Dorset are “of the oldest eutherians known yet in the fossil record.”

“They lie at the base of the branch of the tree that led to placentals and, therefore, us,” he explained.

His observations concluded the teeth were “highly advanced,” evolved to aid in the piercing, cutting, and crushing of food. He also noticed the molars bared marks of extensive usage, suggesting the two animals “lived to a good age for their species.”

The fossilized teeth uncovered in Dorset are thought to have come from two furry, nocturnal species of mammals, one slightly smaller than the other.

The smaller animal, in all likelihood a burrower that probably munched on insects, was no bigger than a mouse. Live Science reports the species was named Durlstotherium newmani, where “Durlstotherium” means “Durlston beast” (a reference to Durlston Bay, where the fossils were unearthed) and “newmani” refers to Charlie Newman, the landlord of a nearby pub not far from where the fossilized teeth were discovered and, BBC News notes, “a keen fossil collector.”

The bigger animal was roughly the size of a juvenile rat and probably supplemented its insect menu with plants. This species was given the name Durlstodon ensomi — “Durlstodon” meaning “Durlston tooth,” while “ensomi” referring to Paul Ensom, a reputed paleontologist whose work pertained to the area.

[Featured Image by S. Fernandez/Wikimedia Commons/Cropped and Resized/CC BY 2.5]