Submerged fossils are revealing long-held secrets from a region known as Sundaland

Over the past 2.5 million years, sea levels have waxed and waned around the islands of Southeast Asia, sometimes exposing a sunken landmass and forming a bridge between islands such as Borneo and Java and mainland Asia. This landscape, called Sundaland, let animals, including hominins, migrate onto the islands of Southeast Asia. Now, scientists have discovered some of Sundaland’s former terrestrial residents. In four studies published in May in Quaternary Environments and Humans, researchers describe the first hominin to be uncovered from this now-sunken landscape, as well as other vertebrate remains.

To Silvia Bello, a paleoanthropologist at the Natural History Museum in London who was not involved with the studies, the new findings offer “unprecedented insight” into the ecosystem that once populated lower Sundaland. She adds that the studies have “paved the way for research into a large and thus far unexplored underwater archaeological record.”

Prior work in what is now Indonesia suggests the earliest hominins in the area were members of Homo erectus, a bipedal hominin that was the first to harness fire and leave Africa. The first of these hominins arrived in the archipelago via Sundaland as early as 1 million years ago. Despite its evidently major role in hominin migration, though, no prior research had uncovered any prehistoric remains from Sundaland: a deficit that Nicholas Flemming, a marine geoarchaeologist at the University of Southampton, calls a “glaring anomaly.”

The new discoveries required digging in the right place—in staggeringly high volumes. In 2014 and 2015, an Indonesian port company dredged about 5 million cubic meters’ worth of sand from the sea floor off Java’s northern coast to build an artificial island. Geologist Harold Berghuis, a consultant with the dredging company, suspected the area might contain important fossils. In 2015, he asked the port authorities whether he could survey the dredged-up island when it was safe to do so.

Once Berghuis got there, fossils were everywhere. It took Berghuis “several lonely months” to scour the 100-hectare island. In all, he collected more than 6300 fossils from dozens of vertebrate species, including panthers, turtles, rhinos, elephants, and Komodo dragons. He uncovered teeth from ancient sharks and rays. He even uncovered one fragment of what he thought might be an ancient human skull.

Berghuis wanted to study the remains himself, but he quickly realized he needed help. So he returned to his home country of the Netherlands and convinced Thijs van Kolfschoten, a paleozoologist at Leiden University, to take him on as a Ph.D. student. “In the course of this long project, I slowly changed from a port consultant into a paleontologist,” says Berghuis, the new studies’ lead author.

To date the fossil cache, Berghuis took sediment samples from a few unbroken blocks of dredged material and the fossil vertebrae of an ancient deer. Based on a dating technique that measures when sunlight last struck the sediments, he found that the fossils were buried between 146,000 and 131,000 years ago. He also closely studied two fossils that looked like hominin skull fragments, which revealed a strong resemblance to H. erectus skulls previously found on Java.

A small sample of fossils gathered by geologist Harold Berghuis, including boar teeth, mandibles, and bovid antler (top row); crocodile teeth from two species (middle row); elephant teeth and mandible and femur fragments from rhino or hippo (bottom row)Harold Berghuis

“We are looking at a very dynamic phase in human history,” Berghuis says. “On mainland Asia we see that the older Homo erectus population is getting replaced by more modern hominins, amongst which were Denisovans and Neanderthals, but on Java—and apparently also on the plains of Sundaland—a relict population of Homo erectus prevailed.”

The haul also reveals how Sundaland’s ancient humans hunted animals. Some of the bones bear tiny cut and break marks consistent with butchery and the breaking open of bones to collect marrow. Berghuis even found some bovid mandibles with cut marks on them, which suggests the Sundaland hominins may have had a taste for tongue. “The evidence of butchery marks on some of the faunal remains suggests that Homo erectus selectively hunted fat-rich prime adult prey,” Bello says. “This is the first time that such evidence has been recorded in Southeast Asia, and is suggestive of complex hunting capabilities by Homo erectus.”

The new discovery might also shed light on how early humans in Southeast Asia evolved into dwarf hominins like Homo floresiensis, which lived on the island of Flores likely between 100,000 and 50,000 years ago. “The most logical model is that a group of Homo erectus somehow got on Flores and developed into a small-bodied island population,” Berghuis says.

Flemming adds that the study demonstrates the value of a “proactive approach” to making underwater discoveries by building collaborations between scientists and heavy industry. “The surface exposure of so many vertebrate remains is astonishing,” he says. Over the next decade, new material recovered from the now-sunken Sundaland should provide a clearer idea of how hominins dispersed—and diversified—across the region’s many islands. “One day, in the not-too-distant future, we will have a real understanding of the distribution of hominin populations on the Sunda Shelf.”