The hominin fossil record between three million years ago and two million years ago is thin, leaving a gap in our understanding of human evolution. Prior to three million years ago (called mega-annum, or Ma), there many fossils of Australopithecus, the apelike hominins that included the famous Lucy. By 2 Ma, there are multiple overlapping fossils clearly belonging to the genus Homo, the group that includes modern humans and all our most direct ancestors. Compared to Australopithecus, these creatures had larger brains, smaller jaws, and stone technology.

The gap is an important one, says Brian Villmoare, a physical anthropologist who analyzes facial characteristics of fossils. This is the period during which our ancestors made the important transition to the more adaptive patterns seen in Homo.

The discovery of a fossilized Homo jawbone, published in Science this week, sheds light on this gap in human evolutionary history. The fossil has features that classify it as belonging to the genus Homo, but it’s approximately 2.8 million years old. This makes it 400,000 years older than the oldest evidence of Homo previously found.