On September 10, 2015, scientists formally announced that a new species of hominin had been discovered in the Rising Star cave system in northern South Africa. But the discovery was far from a secret—the team had live-tweeted their field season earlier. They named the species Homo naledi—for “star” in the local Sotho-Tswana languages.

To date, what scientists know about Homo naledi comes from more than 2,000 fossil fragments that make up 21 individuals—spanning male and female adults as well as infants—from three different parts of the Rising Star’s cave system. The species is estimated to be between 236,000 and 335,000 years old, based on several dating methods. For a science that can count the bones of some entire fossil hominin species with the fingers of one hand, finding soIn the Rising Star cave system, this resulted in a network of chambers, including those where researchers have recovered Homo naledi fossils.

For scientists piecing together the story of South Africa’s ancient environments and evolution, these caves act as time capsules. Over eons, plant and animal remains (not to mention hominins) have been found in the caves. Enough hominin bones were found that in 1999, that region in northern South Africa—and all of its fossil-filled caves—was designated as a 180-square-mile UNESCO World Heritage site called the Cradle of Humankind, dedicated to humanity’s paleoanthropological history.

These bones got into the cave through a number of routes. Rodents, for example, drag bones into the caves and have for millennia. Water from underground sources can move bones from where an animal died to