In what some scientists are calling a “one-in-a-million find,” archaeologists have discovered a cache of butchered rhino bones and dozens of stone tools on the Philippines’s largest island, Luzon. The find pushes back the earliest evidence for human occupation of the Philippines by more than 600,000 years, and it has archaeologists wondering who exactly these ancient humans were—and how they crossed the deep seas that surrounded that island and others in Southeast Asia.
“The only thing missing is the hominin fossil to go along with it,” says archaeologist Adam Brumm, of Griffith University in Nathan, Australia. He’s the one who set the odds for what he calls a “very exciting discovery,” but he wasn’t involved with the work.
Researchers found 75% of a fossilized rhino skeleton—ribs and leg bones still scarred from the tools that removed their meat and marrow—lying in ancient mud that had long since buried an even older river channel. To determine the site’s age, researchers dated the enamel in one of the rhino’s teeth, as well as quartz grains embedded in the sediment layers above and below the bones, using electron spin resonance (ESR), which measures the buildup of electrons as a material is exposed to radiation over time. The team dated the bottom sediment layer to about 727,000 years old, the rhino tooth to about 709,000 years old, and the top sediment layer to about 701,000 years old. Several independent experts say they were impressed by the team’s careful use of the technique. “They’ve nailed it,” says Alistair Pike, an archaeological dating expert at the University of Southampton in the United Kingdom.
So who were these ancient people? They couldn’t have been our own species, Homo sapiens, which evolved in Africa hundreds of thousands of years later. The most likely bet is H. erectus, an archaic human species that first evolved nearly 2 million years ago and may have been the first member of our genus to expand out of Africa, the team writes today in Nature. H. erectus bones have been found in China and Java, so researchers know they lived in Asia around the time the rhino was butchered on Luzon. But Thomas Ingicco, a paleoarchaeologist at the National Museum of Natural History in Paris who led the research, doesn’t want to jump to any conclusions without human bones—especially not in a region that already has yielded one big surprise for scientists studying archaic humans.
Three thousand kilometers to the south, on the island of Flores in Indonesia, archaeologists discovered H. floresiensis, a diminutive archaic human species known as the hobbit. It lived from about 60,000 to 100,000 years ago and seems to have evolved its short stature, large feet, and other distinctive traits because of its long isolation on Flores. There’s no evidence that the rhino butcherers on Luzon are the ancestors of the hobbit, or connected to those unusual humans in any way. But the discovery of H. floresiensis opened up the possibility that there could be many hitherto unknown human species living and evolving in Southeast Asia. “In theory you could have something special on every single island,” Ingicco says.
Equally mysterious is how the ancestors of the rhino butchers arrived on Luzon, which was surrounded by deep water then, as it is today. “I’ve been studying H. erectus for a long time, and I think they are pretty clever,” says Susan Antón, a paleoanthropologist at New York University in New York City who wasn’t involved in the work. Recent research even suggests that stone age peoples were using boats more than 130,000 years ago in the Mediterranean Sea. But like most researchers, Antón isn’t convinced that ancient humans were deliberately crossing Southeast Asian seas so long ago. More likely, they were carried to distant islands by tsunami waves, or arrived there via floating islands of land and debris detached during typhoons. “The presumption has been that Homo erectus didn’t, at least purposefully, disperse over water,” Antón says. “But the more places you find that happening, then … the more likely it becomes that they had some kind of control over it. But that kind of a conclusion is way off in the distance.”