Scientists believe the teeth, found in Dorset, are the earliest known from the line of mammals leading to humans on earth today.
The fossil remains of two rat-like creatures believed to be our oldest known ancestors have been discovered.
The two teeth, from two different species, were found in samples of Cretaceous period rock from cliffs in Swanage, Dorset by student Grant Smith.
The animals – who lived 145 million years ago in the shadows of the dinosaurs – are believed to be ancestors of most mammals living today, including the blue whale, the pygmy shrew and humans.
Dr Steven Sweetman, of the University of Portsmouth, said his “jaw dropped”, when Mr Smith brought him the specimen to have a look at.
He said: “The teeth are of a type so highly evolved that I realised straight away I was looking at remains of Early Cretaceous mammals that more closely resembled those that lived during the latest Cretaceous, some 60 million years later in geological history.
“In the world of palaeontology there has been a lot of debate around a specimen found in China, which is approximately 160 million years old. This was originally said to be of the same type as ours but recent studies have ruled this out.
“That being the case, our 145 million-year-old teeth are undoubtedly the earliest yet known from the line of mammals that lead to our own species.”
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Mr Smith found the teeth in the area dubbed the Jurassic Coast because of the high volume of dinosaur fossils found there.
Dr Sweetman and researchers say the teeth are likely to have come from a burrower, that ate insects, and a larger, plant-eating animal.
The student’s findings were written up by Dr Sweetman and colleagues in the Acta Palaeontologica Polonica journal.
Dr Sweetman added: “The teeth are of a highly advanced type that can pierce, cut and crush food.
“They are also very worn which suggests the animals to which they belonged lived to a good age for their species – no mean feat when you’re sharing your habitat with predatory dinosaurs.”
One of the species has been named Durlstotherium newmani, after Charlie Newman, landlord of the Square and Compass pub in the village of Worth Matravers close to where the fossils were discovered.
The other has been named Durlstodon Ensomi.