A fossilized leg bone collected from Indonesia’s Liang Bua cave in 2009 and initially dismissed as an ordinary bird remain has turned out to belong to a previously unknown species of giant megapode. Estimated to have lived between 190,000 and 120,000 years ago, the ground-dwelling bird weighed about 3.9 kilograms (8.6 pounds), making it the largest member of its genus ever identified in the fossil record.
For nearly 17 years, the small fossil remained largely unnoticed. When researchers first recovered it from Liang Bua, a cave on the Indonesian island of Flores, they recognized it as a bird bone but did not realize it represented something unusual.
A closer examination has now changed that assessment. The fossil belongs to an extinct species named Megapodius rokusi, providing the first fossil evidence of a megapode in Wallacea, the island region between mainland Southeast Asia and Australia.
The discovery is particularly valuable because scientists have relatively little information about the birds that inhabited the region during this period.
“It is one of the oldest bird remains we have found at Liang Bua …,” Hanneke Meijer, a professor and curator of osteology at the University Museum of Bergen, said. “This is a period for which we have almost no data on birds, … so it is exciting that we can pinpoint this species to this period.”
A giant among ground-dwelling birds
Megapodes are chicken-like birds that spend most of their time on the ground. Unlike many other birds, they do not rely on sitting on their eggs to keep them warm. Instead, they bury their eggs or place them in large mounds, leaving environmental heat to help incubate them.
According to Meijer, “Rather than sit on their nests, they (megapodes) lay their eggs in large mounds or burrows and then leave them there (and never look back).”
The group has a long evolutionary history. Megapodes split from other fowl-like birds during the Late Cretaceous, and researchers suggest they first appeared in Australasia before spreading across eastern Indonesia, Melanesia, the Philippines and Australia.
Despite this long history and wide distribution, no fossil evidence of a megapode had previously been reported from Wallacea.
The Liang Bua discovery changes that picture. The bone came from one of the cave’s deepest layers, dating to between 190,000 and 120,000 years ago. The same cave is known for its fossils of Homo floresiensis, the small-bodied ancient human relative discovered on Flores.
The researchers concluded that the leg bone represented a previously unknown species and named it Megapodius rokusi. The name honors Rokus Due Awe, the person who first recognized the bones of Homo floresiensis and later identified the bird fossil.
“Due Awe was an incredible self-taught zooarchaeologist, and it is an honor to be able to name a species after him,” Meijer said.
Larger than any known living megapode in its genus
The fossil also points to an unusually large bird.
Based on the leg bone, the researchers estimated that M. rokusi weighed around 3.9 kilograms (8.6 pounds). That would make it the largest known member of the genus Megapodius.
For comparison, Flores is still home to the orange-footed scrubfowl, a living megapode that weighs between 0.5 and 1.2 kilograms (about 1–3 pounds). The extinct species would have been several times heavier.
Its size makes the fossil especially interesting, but the single bone leaves much of the bird’s biology unknown.
Researchers cannot say whether M. rokusi could fly because no wing bones have been found. Nor can they determine exactly when the species disappeared.
The study raises the possibility that it became extinct around the same time as several other animals known from Liang Bua, including a giant stork, a dwarf Stegodon, Homo floresiensis and vultures. But it could also have vanished much earlier. The available fossil evidence does not establish which possibility is correct.
A missing part of Wallacea’s prehistoric wildlife
The discovery also raises questions about why megapode fossils have remained absent from the region’s fossil record.
Bird bones are often overlooked in fossil collections, where researchers have traditionally paid greater attention to the remains of mammals. Meijer suspects that other megapode fossils may already exist among previously collected material but have not yet been recognized.
That possibility matters because the animals living in Southeast Asia today represent only part of the region’s former biodiversity.
“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,” Meijer said.
The newly identified species offers a glimpse of that lost diversity, although much remains unknown about its appearance, behavior and eventual disappearance. More fossils would be needed to reconstruct those aspects of its life.
Meijer believes the Liang Bua bone may be only the beginning of a larger story about prehistoric birds in Wallacea.
“I definitely think there might be more megapode fossils lying around, and I can’t wait to look at more material to find them,” Meijer said.
The research was published in Alcheringa: An Australasian Journal of Palaeontology.
