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takyon writes:

Fossils of Some of Our Oldest Mammal Ancestors Found

Two ancient teeth found in southern England are some of the oldest known fossils from the group of mammals that gave rise to humans. The teeth likely belonged to ancient creatures that nibbled on insects and went out only at night—a life strategy that let them avoid the dinosaurs that dominated Earth during the Cretaceous.

The teeth represent two newfound species of early mammal, both of which vaguely resembled small shrews. The smaller animal, named Durlstotherium, in all likelihood ate insects almost exclusively. The larger one, named Durlstodon, may have had hefty enough teeth for processing plant material, but researchers can't be certain.

[...] According to [Steve Sweetman's] analysis, the teeth are roughly 145 million years old, the age of the rock formation in which they were found, and they're dead ringers for eutherian mammals. This group includes today's placental mammals—such as dogs, elephants, and humans—and their now-extinct kin.

[...] The timing of the first eutherians has been a matter of debate. Based on fossil and genetic evidence, some paleontologists suggest that they've been around since at least the late Jurassic, about 160 million years ago, while some studies imply that they may have arisen later. If this analysis holds, the new fossils, unveiled this week in Acta Palaeontologica Polonica [open, DOI: 10.4202/app.00408.2017] [DX], hold the record for the oldest eutherian remains ever found in Europe, adding a crucial piece of hard evidence to the debate. (The oldest eutherian known today, a Chinese fossil called Juramaia [DOI: 10.1038/nature10291] [DX], is about 15 million years older, but some researchers argue that it's not a eutherian.)

Also at The Guardian and Live Science. Eutheria.

Related: Flying Squirrel-Like Mammals Lived 160 Million Years Ago

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