These Rodent-Like Creatures Are the Earliest Known Ancestor of Humans, Whales and Shrews

The earliest known ancestors of the mammal lineage that includes everything from humans, to blue whales, to pygmy shrews may have been nocturnal, rodent-like creatures that evolved much earlier than previously thought.

The identity of these ancestors comes from their teeth, which were discovered at cliffs on the coast of England. The discovery of the little creatures, which lived about 145 million years ago, may push the evolution of this mammal group back dozens of millions of years, the researchers said.

The lineage known as the eutherians includes the vast majority of all living mammals. The group excludes marsupials such as kangaroos, which carry young in pouches, as well as monotremes such as platypuses, which lay eggs. [In Photos: See How Mammals Changed Over Time]