Buried 6½ feet beneath volcanic rock on the Indonesian island of Flores, the fossilized remains of a petite hominin that lived 700,000 years ago have been discovered by scientists.

The discovery, described Wednesday in two papers in Nature, consists of just six tiny teeth and a fragment of a small lower jawbone. Still, the international research team said it is enough to suggest that the fossils belonged to a direct ancestor of the strange and diminutive human relative Homo floresiensis, also known as the “Hobbit.”

The find could help scientists unravel the mysterious origins of this enigmatic human species — nicknamed the Hobbits for their miniature size — that was isolated on a small island between Asia and Australia for at least 1 million years.

The world was first introduced to Homo floresiensis in 2004, when an international team of researchers announced the discovery of a never-before-seen hominin that had been found in the Liang Bua cave on Flores. The fossil record suggests that these ancient human relatives lived between 100,000 and 50,000 years ago. Adults stood just 3½ feet tall — the height of an average 4-year-old modern-day child.

But the new fossils found at Mata Menge were even smaller. The researchers estimate the jawbone was 23 percent smaller than the Homo floresiensis jaw found at Liang Bua.

“They were truly little people, smaller even than the Liang Bua Hobbits,” said Richard Roberts of the University of Wollongong, who was part of the original discovery team but was not involved in the new study.

In the intervening years, competing views of the Hobbits’ origins emerged. One hypothesis posits that Homo floresiensis descended from the large-bodied hominin Homo erectus that lived between 1.89 million and 143,000 years ago.

Scientists say it is possible that Homo erectus may have arrived on Flores from Java, perhaps after being washed out to sea by a tsunami. Over time, this species began to shrink on its new island home — known as island dwarfism.

The other hypothesis is that Hobbits descended from smaller and more ancient hominins such as Australopithecus africanus or Homo habilis that were already diminutive at the time they reached the island.

Both theories have challenges. One might accept that Homo erectus grew smaller in stature by two-thirds over time. After all, a smaller body is easier to feed. But for some scientists, it is hard to believe that it made evolutionary sense for its brain to shrink by half. Losing brain power doesn’t seem like a likely evolutionary development.

On the other hand, if you buy that Homo floresiensis was descended from Australopithecus or Homo habilis, then you have to explain how either of these species made their way to Indonesia when their remains have never been found outside of Africa.

Other researchers are convinced that the Hobbit fossils belonged to anatomically modern humans who had some type of disorder, such as microcephaly or Down syndrome.

But in another study published Wednesday in the journal PLOS One, Karen Baab, a paleoanthropologist at Midwestern University in Glendale, Ariz., and her colleagues concluded that any resemblance between people with Down syndrome and the fossils was superficial and that the fossils belonged to a separate species.

A total of 30,000 fossils were unearthed during excavations led by Gerrit van den Bergh of the University of Wollongong in New South Wales, Australia; Adam Brunn of Griffith University in Queensland, Australia, and Iwan Kurniawan of the Geological Museum in Bandung, Indonesia.

Digging at the Mata Menge site is not easy. The fossils are embedded in solid rock, not sediments. To uncover them, researchers spent years chipping away at stone in unrelenting heat. It wasn’t until 2014, 20 years after the work there began, that researchers recognized a molar belonging to a hominin in a layer of sandstone dated to 700,000 years ago.

A few days later the group unearthed a mandible fragment — the lower piece of a jawbone in the same layer. A handful of other teeth followed.

Yousuke Kaifu, a biological anthropologist and ancient-hominin tooth specialist from the National Museum of Nature and Science in Tokyo, initially thought the mandible belonged to a juvenile because it was so tiny. But they discovered a wisdom tooth erupting from the jaw. “That means that it was an adult,” Van den Bergh said.

A close examination of the number and placement of cusps or bumps on the individual teeth revealed that they were very similar, although not identical, to teeth that had been discovered at Liang Bua. They were also, unexpectedly, up to 28 percent smaller than the teeth from Liang Bua. “That was a surprise,” Van den Bergh said. “Mata Menge is more than half a million years older than Liang Bua. We thought we would find something bigger — something closer to the initial founder population.”

Kaifu’s analysis also showed that the Mata Menge teeth were more similar to Homo erectus teeth than to teeth from Australopithicus or Homo habilis.

And so now, a more definitive story of the origin of the Hobbit can be told. The earliest known evidence of stone tools on Flores dates to 1 million years ago, suggesting that hominins arrived on the island around that time. If these first colonizers were indeed Homo erectus, then it seems that they rapidly evolved a small stature within 300,000 years of their arrival — a shorter time span than was previously thought.

 

The New York Times contributed to this report.