Scientists Found Evidence of Our Ancient Human Ancestors Underwater, Suggesting a Sunken World

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Fragments of a Homo erectus skull were among deposits of vertebrate fossils found when the Indonesian seafloor was being dredged for a construction project
This is the first time fossils of this species have been found on the seafloor between the islands of Indonesia, and further investigation found that land bridges once connected the islands.
Evidence of Homo erectus hunting bovine ancestors and extracting bone marrow was also discovered.

During the glacial period that chilled the Earth 140,000 years ago, sea levels in the Indonesian region of Sundaland were low enough for present-day islands to tower like mountain ranges with a lowland savannah stretching between them. It was an expanse of mostly dry grasslands with strips of forest edging the rivers, and animals like crocodiles, river sharks, elephants, hippos, rhinos, and carnivorous lizards flourished in the region.

Sundaland was also a paradise for early humans. Long thought to have been isolated on the island of Java, two fossil fragments of a Homo erectus skull—which surfaced with recent ocean dredging in preparation for the construction of an artificial island—revealed that this hominin species migrated and spread throughout the islands when they could still walk over bridges of land.

Homo erectus was first discovered in Java (and was known as “Java Man” until the species was officially renamed), but sossilized remains had never before been found on the seafloor between what are now the islands of Java, Bali, Sumatra and Borneo. Now that examples have been dredged up, however, Harold Berghuis—an archaeologist from the University of Leiden in the Netherlands, who led the investigation —thinks Homo erectus took advantage of the now-drowned land, and likely settled near the riverbanks in the region.

“Under the relatively dry Middle Pleistocene climate of eastern Java, herds of herbivores and groups of hominins on the lowland plains were probably dependent on large perennial rivers, providing drinking water and terrestrial as well as aquatic food sources,” Berghuis said in a study recently published in Quaternary Environments and Humans.

These human ancestors would have had plenty to take advantage of near these ancient rivers. Trees bore fruit all year, and the ancient hominins would have been able to gather edible plants in addition to catching fish and shellfish. They may have even used mussel shells as tools—the oldest known evidence of them being used for that purpose—and engraved some of them (the most ancient human engravings have been found on shells that previously turned up in Java). The new findings show that they also hunted river turtles and terrestrial animals. Bones of river turtles and bovine ancestors showed cut marks and breakages that suggested the consumption of both meat and bone marrow.

More modern human species on the Asian mainland (such as Denisovans and Neanderthals) were already known to have hunted bovids, and while no evidence for this had been found on Java, the presence of these seafloor fossils could mean that hunting methods were transferred from one species to the other. There may have even been interbreeding. Land exposed by diminished sea levels also meant that animal species from the mainland—like the extinct Asian hippo and the endangered (but still-extant) Komodo dragon—could spread to the Indonesian islands.

Homo erectus marked a significant shift in human evolution—they were the earliest hominids to bear more of a resemblance to modern humans, with larger bodies, longer legs, and shorter arms relative to their torso. More muscle mass meant that they could walk and run faster than earlier hominins, and were likely more adept hunters. An increase in body size is also associated with an increase in brain size, and skulls tell us that their brains were over 50% larger than those of early Australopithecus species (though the human brain would eventually evolve to be 40% larger than that by the time Homo sapiens appeared).

“The late Middle Pleistocene age of the site is of great interest in terms of hominin evolution, as this period is characterized by a great morphological diversity and mobility of hominin populations in the region,” Berghuis and his team said.

When sea levels rose, the land bridges between the islands of Sundaland were submerged, but this dredging has given us an unprecedented window into the life of Homo erectus in Indonesia.

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