Giant extinct bird identified from single bone in cave that held "hobbit" human fossils

Paleontologists have identified a new species of extinct ground bird from a single fossil leg bone recovered inside Liang Bua, the limestone cave on the Indonesian island of Flores famous as the site where the diminutive hominin Homo floresiensis was discovered in 2003. The bird, a giant relative of today's chicken-sized megapodes, lived in the same cave system tens of thousands of years before modern humans reached the island, according to a paper published in the journal Alcheringa: An Australasian Journal of Palaeontology.

The species has been named Megapodius rokusi. It is the first fossil megapode ever described from Wallacea, the biogeographically distinct zone of islands between Asia and Australia that includes Flores, and it is the largest member of its genus known to science, living or extinct.

A single bone, a big bird

The fossil itself is modest: the lower half of a right tarsometatarsus, one of the long bones of a bird's lower leg, cataloged as LB-Av-1542. It was excavated in 2009 from one of the deepest and oldest sediment layers at Liang Bua and set aside, unidentified, until the research team compared it against the skeletons of living and extinct megapodes.

Based on the bone's dimensions, the researchers estimate the bird weighed roughly 3.9 kilograms, or about 8.6 pounds. That is several times the mass of the only megapode living on Flores today, the orange-footed scrubfowl, which typically weighs between 0.5 and 1.2 kilograms. The sediments that held the bone date to somewhere between about 190,000 and 120,000 years ago, placing the bird well within the span of Pleistocene fauna that once populated the cave alongside pygmy elephants, Komodo dragons and, eventually, Homo floresiensis itself.

Megapodes, which include living genera found across Southeast Asia, Australia and the Pacific, are unusual among birds for the way they reproduce. Rather than incubating eggs on a nest, they bury them in large mounds of sand, soil or volcanic ash and leave the heat of decomposition or geothermal activity to do the work. Without wing or shoulder bones to examine, the authors say they cannot determine whether Megapodius rokusi retained the ability to fly, a trait some island megapodes lost entirely.

A record of vanished fauna

Liang Bua has produced one of the more detailed fossil records of extinction in island Southeast Asia. Besides H. floresiensis, excavations at the cave, which began in earnest in 2001 under Indonesian field coordinator Thomas Sutikna, have yielded the remains of a dwarf relative of the elephant known as Stegodon, giant rats, an extinct vulture and an extinct giant marabou stork, several of which disappear from the cave's layers at around the same time as the hobbit-sized hominin, roughly 50,000 years ago. Researchers, including Lakehead University paleoanthropologist Matthew Tocheri, who helped establish that revised chronology in a 2016 reanalysis of the site's sediments, have long noted that the cause of this broader faunal turnover remains unresolved. The new megapode adds one more entry to that list of island species that vanished without a clearly identified cause, whether climate shifts, volcanic disruption or the eventual arrival of modern humans.

The species name honors Rokus Due Awe, the Indonesian excavator who first recognized the significance of the bones that would become the H. floresiensis holotype and who later identified the leg bone itself as avian. Hanneke Meijer, the paper's lead author and a paleontologist and curator of osteology at the University Museum of Bergen in Norway, described Due Awe in comments reported by Phys.org as "an incredible self-taught zooarchaeologist" and said naming a species after him was "an honor." The study's other authors, Sutikna, E. Wahyu Saptomo and Tocheri, have worked together on Liang Bua material for more than a decade, and all were involved in the original excavation and dating of the hominin remains described by the Smithsonian's Human Origins Program and other researchers.

Why a single leg bone matters

For researchers who study the biogeography of Wallacea, a single bone from a previously undocumented species carries weight disproportionate to its size. Islands such as Flores, isolated for long stretches of geological time, tend to produce unusual evolutionary outcomes: dwarfed elephants, a diminutive hominin and, now, an oversized ground bird. Meijer, whose account of the discovery was also covered independently by the science-news outlet Sci.News, said the find highlights how incomplete the fossil record for the region still is.

"Southeast Asia is considered a biodiversity hotspot, but it is important to realize that what we see today is only a remnant of what once was."

That remark reflects a broader concern among paleontologists and conservation biologists working in the region: current inventories of Southeast Asian and Wallacean wildlife, however rich, likely understate the diversity that existed even in the relatively recent geological past, before a wave of late-Pleistocene extinctions whose causes are still debated. Conservationists tracking the status of living megapodes, several species of which are already threatened by habitat loss and egg harvesting across Indonesia and the Pacific, have cited that same pattern of historical loss as a caution against complacency about currently stable populations.

What comes next

The immediate scientific questions are narrow but unresolved. Researchers do not know when Megapodius rokusi went extinct, whether it persisted until the arrival of modern humans on Flores around 46,000 years ago, or whether it disappeared earlier for unrelated reasons. Nor can they say, absent wing material, whether the species flew at all, a detail that would clarify how it dispersed to or evolved on the island in the first place.

Meijer has said she expects more bird material to turn up as collections from decades of Liang Bua excavation are re-examined, noting there are likely additional megapode fossils "lying around" in existing collections that have not yet been matched to a species. The team's broader project, a systematic reassessment of the cave's full faunal record, continues alongside ongoing study of the hominin remains themselves, work that has already revised the timeline of H. floresiensis's disappearance once and could still revise it again as new material, or new identifications of old material, comes to light. For now, the bird adds one more data point to a site that, more than two decades after it produced one of paleoanthropology's most debated discoveries, continues to yield new species from bones first pulled out of the ground years or even decades ago.