A strange new species may have joined the human family. Human fossils found in a cave on Luzon, the largest island in the Philippines, include tiny molars suggesting their owners were small; curved finger and toe bones hint that they climbed trees. Homo luzonensis, as the species has been christened, lived some 50,000 to 80,000 years ago, when the world hosted multiple archaic humans, including Neanderthals and Denisovans, and when H. sapiens may have been making its first forays into Southeast Asia.
“This is a truly sensational finding,” says Adam Brumm, an archaeologist at Griffith University in Nathan, Australia. The paper, published this week in Nature, “sent shivers down my spine.”
The discovery echoes that of another unusual ancient hominin—the diminutive H. floresiensis, or “hobbit,” found on the island of Flores in Indonesia. “One is interesting. Two is a pattern,” says Jeremy DeSilva, an expert on Homo foot bones at Dartmouth College. He and others suspect the islands of Southeast Asia may have been a cradle of diversity for ancient humans, and that H. luzonensis, like H. floresiensis, may have evolved small body size in isolation on an island.
In 2007, a team led by Armand Mijares, a paleoanthropologist at the University of the Philippines in Quezon City, found a metatarsal—one of the bones that runs along the top of the foot—in Callao Cave on Luzon. The shape of the bone clearly marked its owner as a member of our genus, the team reported in 2010. The ratio of uranium to its decay products in the bone revealed its probable age range, between 50,000 and 80,000 years old, with a likely minimum age of about 67,000 years. Intrigued, Mijares’s team went back in 2011 and 2015—and excavated what he calls a fossil “bonanza.”
In the same layer as the metatarsal, the team discovered five teeth from the right upper jaw of the same individual, two isolated teeth, two finger bones, two toe bones, and a broken femur. The bones represent at least three individuals, the team says, all presumably from the same species.
The teeth show a unique mosaic of traits found separately in other Homo species. The premolars are about the size of ours, but instead of a single root they have two or three—a primitive feature. The molars are much more modern, with single roots, but “incredibly small” at only 10 millimeters long and 8 millimeters across, says Florent Détroit, a paleoanthropologist at the Museum of Man in Paris who worked with Mijares. That’s even smaller than those of H. floresiensis. Tooth size tends to correlate with body size, so it’s possible that H. luzonensis itself was tiny, Détroit says. But only a complete arm or leg bone will say for sure.
The long, curved fingers and toes resemble those of australopithecines like Lucy, an early human ancestor thought to have both walked upright and swung through the trees. “This is a very strong indication of climbing,” says paleoanthropologist Tracy Kivell, who studies hand bones at the University of Kent in Canterbury, U.K.
Not everyone is ready to embrace these teeth and skeletal fragments as a separate species, rather than a locally adapted population of, say, H. erectus, an older hominin that lived in Asia for millennia.
“I see what they’re saying, but at the same time, I want more,” says Susan Antón, a paleoanthropologist at New York University in New York City. A skull bone could clinch the case for a new species, as could ancient DNA. But DNA breaks down fast in hot, humid conditions like those at the cave, and the fossils have not yielded genetic material.
Regardless of whether H. luzonensis was its own species, it may have evolved in isolation for hundreds of thousands of years. Butchered rhino bones on Luzon date to 700,000 years ago, though researchers don’t yet know which human species was responsible.
Mijares is already back in the field. Many more pieces of the human story could be hidden on Southeast Asia’s islands. When it comes to human evolution, Antón says, “We know a lot less than we thought we did.”
Source : Sciencemag.com | nature.com
