In October 2004, excavation of fragmentary skeletal remains from the island of Flores in Indonesia yielded “the most important find in human evolution for 100 years.” In 60,000 to 100,000-year-old sediments of the Liang Bua cave, archaeologists discovered a previously unknown human species later described as Homo floresiensis, dubbed by the media “The Hobbit” due to the reduced size of this hominid.
H. floresiensis displays some very unusual anatomical characteristics: a cranial volume reported as only 380 milliliters, suggesting a brain less than one-third the size of an average modern human’s, and short thigh bones, which were used to reconstruct a hominid standing just 1.06 meters tall.
The Liang Bua cave also contained bones of rodents of extraordinary size, pigmy elephants, an oversized Komodo dragon species, and fragmentary remains of a giant bird.
Leptoptilos robustus is the first fossil bird species described from the island of Flores. This extinct marabou stork was a giant, standing 1.8 meters tall, towering over the small H. floresiensis.
Previous research suggested that L. robustus evolved from a smaller Asian ancestor species and was too large and heavy to fly. Birds tend to reduce their wings on islands without natural enemies, preferring to walk and hunt prey on the ground. During the Pleistocene, about two million years ago, the island of Flores was cut off from the mainland by rising sea levels. As large carnivorous mammals never made it to the island, Leptoptilos evolved to become an apex predator and scavenger in the local ecosystem.
But the discovery of wing bones in recent excavations shows that the wings of Leptoptilos were well developed. Also, there was no reduction in the skeletal system as seen in modern flightless birds, like ostriches, suggesting that powerful muscles attached to the bones, allowing powered flight.
It is unclear if Leptoptilos actively preyed on Homo floresiensis, or why fossils of H. floresiensis were found buried together with Leptoptilos bones. Likely the birds entered Liang Bua cave in search of carcasses of animals butchered by H. floresiensis. The discovery of stone tools shows that this human species, despite the smaller brain, was able to process, maybe even actively hunt, large prey.
The paper “More bones of Leptoptilos robustus from Flores reveal new insights into giant marabou stork paleobiology and biogeography” is published in Royal Society Open Science (2022).