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.
Steve Sweetman, a research fellow, co-authored a paper on the findings in the Polish-based quarterly journal Acta Palaeontologica Polonica.
Fossils of the oldest-known ancestors to mammals, including human beings, has been discovered in Dorset by undergraduate student Grant Smith whilst working on his dissertation. The second is a tribute to a man called Charlie Newman, who is not a palaeontologist but is, in fact, the landlord of a pub called the Square and Compass - the nearest place to the cliffs in which fossil hunters can get a beer.
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. "They are also the ancestors to most mammals alive today, including creatures as diverse as the Blue Whale and the Pigmy Shrew", the online magazine Heritage Daily reported. This was originally said to be of the same type as ours but recent studies have ruled this out.
Dr Sweetman, whose research interests includes small vertebrates which lived with the dinosaurs, identified the teeth.
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"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". The team also believes the critters were furry and nocturnal. The other has been named Durlstodon Ensomi.
The rat-like creature had highly advanced teeth that allowed it to pierce, cut and crush through food and it's suspected that the creature was a burrower and feasted upon insects.
The fossil teeth as seen under a microscope. "No mean feat when you're sharing your habitat with predatory dinosaurs!"
Smith said that he knew he was looking at something mammalian but didn't realize he had discovered something quite so special.
The discovery was made along Dorset´s "Jurassic Coast", a UNESCO World Heritage Site which charts 185 million years of history.