Fossilized teeth show that two different kinds of ancient human ancestors coexisted more than 2 million years ago. One of them may be an unknown species.

Researchers have unearthed tooth fossils in Ethiopia dating to about 2.65 million years ago of a previously unknown species in the human evolutionary lineage, one that lived in the same time and place as the earliest-known member of the genus Homo to which our own species belongs.

In the dry, rugged badlands of Ethiopia’s Afar Region, a team of scientists has uncovered fossils that could change how you picture human evolution. These finds, dating back between 2.6 and 2.8 million years,