Skulls from central Java may come from the last surviving population of Homo erectus, suggests a new study dating the fossil bed and the surrounding landscape. The population’s death roughly coincides with dramatic changes in the environment, which may have caused the species’ extinction long before the first Homo sapiens reached Southeast Asia.

The “last stand” of Homo erectus?

University of Iowa anthropologist Russell Ciochon and his colleagues dated fossils and sediment layers from a site called Ngandong in a naturally terraced valley carved out of the surrounding hills by the Solo River. In the 1930s, archaeologists unearthed the tops of a dozen Homo erectus skulls, along with two tibiae (shin bones). These fossils seem to be different from older Homo erectus fossils in some important ways, like much larger cranial capacity (which suggests bigger brains) and higher foreheads.

“Ngandong Homo erectus has the largest brain size and highest foreheads of any known Homo erectus,” Macquarie University geochronologist Kira Westaway, a co-author of the study, told Ars. “This indicated an important evolutionary change. The timing of this change is crucial to our interpretation and understanding of our distant cousins.”