Earliest Known Ancestor Of Mammal Lineage That Gave Rise To Us Discovered In Southern England

The two little species identified lived in the shadows of dinosaurs, and so were likely nocturnal. Dr Mark Witton

Humans come from a long distinguished line of creatures, which has now been traced back to a small shrew-like critter that scurried around the feet of dinosaurs in what is now southern England some 145 million years ago.

This, the researchers believe, is the earliest known ancestor of the group of animals that contains most living mammals, from the mighty blue whale to the teeny bumblebee bat.

The incredible discovery was made by an undergraduate at the University of Portsmouth, who was simply sifting through material collected from the Cretaceous rocks that form the coastline of Dorset when he came across two tiny teeth. While he suspected what they were, it was not until Dr Steve Sweetman looked at them that their significance became clear.

“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,” explained Dr Sweetman, who identified the teeth as belonging to an early mammal, and coauthored the paper to be published in Acta Palaeontologica Polonica.

He thinks that the teeth clearly once belonged to an early eutherian mammal, which is the same lineage that we as a species belong to, but different from that of both marsupials and monotremes. The creature the teeth belonged to was likely a furry nocturnal animal, something that was also the feature of another recent study. It probably ate a variety of foodstuff, ranging from insects to plant material, with the wear on the two teeth suggesting that the creature to which they once belonged likely lived to a decent age.

There has been a lot of debate among experts as to when the first eutherian mammals evolved, with much of this being focused on a specimen found in China that dates back around 160 million years, although there is no consensus yet as to whether or not this Chinese fossil is what the authors say it is. When the researchers made this latest discovery in Dorset, there were some suggests that perhaps it was from the same species as the disputed Chinese example, but this was ruled 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,” said Dr Sweetman.

The two teeth are thought to have belonged to not only two different animals, but also two different species. One has been named Durlstotherium newmani, after the landlord of a local pub, while the other is Durlstodon ensomi, after a local palaeontologist.

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