Incredibly Tiny New Fossil Arm Bone May Resolve Mystery Of Ancient Hobbits’ Family Tree

Three new fossils, including part of a humerus, have been found at Mata Menge on the Indonesian island of Flores. They suggest that Homo floresiensis , popularly known as Hobbits, were descended from Homo erectus , and became small relatively soon after arriving on Flores. Indeed, it seems at least some Hobbits from 700,000 years ago were even smaller than the ones whose diminutive size earned them the nickname.

The discovery of specimens from Liang Bua cave on Flores stunned the world, revealing that a species of human we had known nothing about had coincided with modern humans. Indeed, the timing suggested our ancestors probably reached the island in time to encounter these diminutive people, and were quite likely responsible for their extinction. With the Lord of the Rings films filling the cinemas and H. floresiensis standing only 1.1 meters (3.6 feet) high, the nickname was inevitable.

What was less clear was where the Hobbits fitted into the human family tree. The most obvious explanation was that they were descendants of H. erectus , known to have been a few hundred kilometers away in Java from considerably earlier. The phenomenon of island dwarfism , where species shrink when confined to limited locations, is widespread (as is its counterpart, island gigantism ). Dwarf stegodons (elephant relatives) are known to have inhabited Flores along with the hobbits.

However, some features of the Liang Bua Hobbits' postcranial skeleton looked less like H. erectus and closer to more ancient human ancestors such as H. habilis and Australopithecus afarensis (made famous by the individual Lucy .) A more extraordinary tale needed to be considered, where one of these ancestors, previously known only from Africa, somehow made it all the way to Southeast Asia’s islands. Since these forebearers were already quite small, little island dwarfism would be needed to explain the Hobbit’s height.

The discovery of teeth, stone tools, and partial jaw at Mata Menge , also on Flores, in 2014 raised hopes of settling the question. These remnants were from 700,000 years ago, and appeared to also be from Homo floresiensis. Now a team including Dr Gerrit van den Bergh of the University of Wollongong have found three new fossils of the same age, which make those who have examined them more confident of the Hobbits’ story.

We originally thought it must be from a child.

Dr Gerrit van den Bergh

The 2014 finds appeared small, but they were not the best body parts to measure the whole person’s size, which is why the humerus, partial as it is, is so important. It’s tiny, but investigation reveals it comes from an adult, unlike some of the teeth at Mata Menge, which are from children.

“This 700,000-year-old adult humerus is not just shorter than that of Homo floresiensis , it is the smallest upper arm bone known from the hominin fossil record worldwide,” said Professor Adam Brumm of Griffith University in a statement .  “This very rare specimen confirms our hypothesis that the ancestors of Homo floresiensis were extremely small in body size; however, it is now apparent from the tiny proportions of this limb bone that the early progenitors of the ‘Hobbit’ were even smaller than we had previously thought.”

This bone was 9-16 percent shorter and thinner than the equivalent from the Liang Bua Hobbits.

Van den Bergh told IFLScience the bone is so small “We originally thought it must be from a child.” Bones can often be identified as adults when their extremities (the epiphyses) have fused with the shaft. However, team members looked at the microstructure of a small piece. “The outside of bone is laminated,” van den Bergh said, “but it gets remolded over time, the outside is lost, and it is replaced with other bone.” The ratio of the two bone types does not provide a reliable age, but can distinguish adults from children, which was all that was needed in this case.

The fact one adult Hobbit was probably just 1 meter (3.3 feet) tall 700,000 years ago might be considered evidence for their descent from already small species. However, the authors argue the two new teeth found in the same dig show a clearer affiliation with H. erectus than those located earlier.

Van den Bergh told IFLScience, “We don’t know why the cranial and skeletal structures from Liang Bua have features similar to H. habilis . Maybe on Flores they spent more time in the trees and adapted to the local conditions.” Given that the other inhabitants of Flores included Komodo dragons with iron-tipped teeth , rediscovering your ancestors’ arboreal skills does seem wise.

The authors conclude that a H. erectus population arrived on the island 1.0-1.27 million years ago and shrank dramatically in stature by 700,000 years ago. Whether they rebounded a little by the time of the original finds, or if one of the specimens was unrepresentative of their time will take more specimens to answer.

This still leaves the question of how H. erectus reached Flores, which was never connected to mainland Southeast Asia. The paper describing the new fossils proposes they got there “Probably unintentionally (ie through accidental ‘rafting’, perhaps on tsunami debris).” Van den Bergh notes tsunamis are common in the highly volcanic Indonesian islands and points to examples of people surviving at sea for a long time while clinging to branches afterwards.

On the other hand, recent evidence that early humans crossed the Strait of Gibraltar , where tsunamis are unlikely, even earlier suggests they may have had more boat-building skills than has been acknowledged. Van den Bergh admitted to IFLScience that this is a part of the Hobbit’s story we may never know.

The work is open access Nature Communications .