A recent discovery in the seas off Java’s northeast, in the Madura Strait, is giving a previously unimaginable insight into the life of Homo erectus in the late Middle Pleistocene. Researchers dredged the seabed and found more than 6,000 fossilized remains, including two fragments of skull that have been identified as Homo erectus—the first time fossils like these have been found in the submerged lowlands of ancient Sundaland.

Facial reconstruction of Homo erectus, pH๏τographed at the David H. Koch Hall of Human Origins, Smithsonian National Museum of Natural History. Credit: Ryan Somma, CC BY-SA 2.0

The discovery, a collaborative project between Leiden University and Indonesian, Australian, German, and Japanese specialists, was made during marine sand dredging operations near Surabaya. The fossils, now housed in the Geological Museum at Bandung, were discovered in an ancient river valley now submerged—a member of the Solo River system. The study, published in Quaternary Environments and Humans, used optically stimulated luminescence (OSL) techniques to estimate that the valley fill dates to between 163,000 and 119,000 years ago, placing it in the penultimate glacial period (Marine Isotope Stage 6).

“This makes our discoveries truly unique,” said Harold Berghuis, an archaeologist from Leiden University involved in the excavation. “The fossils come from a drowned river valley, which filled up over time with river sand. We have been able to date the material to approximately 140,000 years ago.”

The five facies of the extracted material, based on uncrushed sediment blocks from the BMS reclamation site. Credit: Berghuis et al., Quaternary Environments and Humans (2025)

During times of low sea level, Sundaland, which is now submerged, was a vast lowland that connected Java with the Asian mainland. This region, similar to the present-day African savannah, had elephants, rhinos, crocodiles, hippos, Komodo dragons, and even river sharks. The newly uncovered fossils reveal that Homo erectus lived in this region, where there was constant availability of water, shellfish, fish, and edible plants. Notably, researchers also found cut marks on turtle bones and numerous broken bovid bones, which suggest that these early humans scavenged and actively hunted large prey and processed them for meat and bone marrow.

“Among our new finds are cut marks on the bones of water turtles and large numbers of broken bovid bones, which point to hunting and consumption of bone marrow,” Berghuis said.

The team believes that these behaviors were learned through interaction with other mainland Asian hominin groups, which may be due to cultural exchange or interpopulation interbreeding. This challenges the ᴀssumption that the Javanese Homo erectus was completely isolated.

Credit: Leiden University

The site itself is considered a transitional geological unit in which fluvial Solo River deposits eventually gave way to marine sediments. This reflects a drastic shift in environment from river valleys to estuarine environments due to an increase in sea levels during the warm interglacial stage referred to as MIS 5e. The transition in the valley from terrestrial to tidal conditions provided ideal conditions for the preservation of a diverse range of vertebrate fossils.

Berghuis noted, “Often, only the most attractive material is published in this type of research, such as hominin fossils. We present the results of our studies in four extensive, richly illustrated articles, creating a unique window into the drowned Sundaland of 140,000 years ago.”

The discovery in the Madura Strait expands earlier discoveries at sites like Trinil, Sangiran, and Ngandong—the latter being one of the final strongholds of Homo erectus. Unlike those earlier highland or mid-reach river terrace sites, the Madura Strait is a lowland habitat, possibly with lower rainfall and with distinct vegetation and fauna profiles. The Brantas and Solo rivers would have made this lowland region an especially attractive corridor for humans and animals during times of climatic stress.

This discovery is not only rewriting the history of Homo erectus in Southeast Asia but also providing key context for understanding human adaptation, environmental exchange, and the patterns of Middle Pleistocene migration.

More information: Leiden UniversityBerghuis, H. W. K., Veldkamp, A., Adhityatama, S., Reimann, T., Versendaal, A., Kurniawan, I., … Joordens, J. C. A. (2025). A late Middle Pleistocene lowstand valley of the Solo River on the Madura Strait seabed, geology and age of the first hominin locality of submerged Sundaland. Quaternary Environments and Humans, (100042), 100042. doi:10.1016/j.qeh.2024.100042