By Emma Brennand
Earth News reporter
Artistís impression of the size of the giant stork next to a Homo floresiensis hobbit
A giant marabou stork has been discovered on an island once home to human-like 'hobbits'.
Fossils of the bird were discovered on the Indonesian island of Flores, a place previously famed for the discovery of Homo floresiensis, a small hominin species closely related to modern humans.
The stork may have been capable of hunting and eating juvenile members of this hominin species, say researchers who made the discovery, though there is no direct evidence the birds did so.
The finding, reported in the Zoological Journal of the Linnean Society, also helps explain how prehistoric wildlife adapted to living on islands.
Tall and heavy
The new species of giant stork, named Leptoptilos robustus, stood 1.8m tall and weighed up to 16kg researchers estimate, making it taller and much heavier than living stork species.
Palaeontologist Hanneke Meijer of the Smithsonian National Museum of Natural History in Washington DC, and affiliated to the National Museum of Natural History in Leiden, the Netherlands, made the discovery with colleague Dr Rokus Due of the National Center for Archaeology in Jakarta, Indonesia.
Finding large birds of prey is common on islands, but I wasn't expecting to find a giant marabou stork
Palaeontologist Hanneke Meijer
They found fossilised fragments of four leg bones in the Liang Bua caves on the island of Flores.
The bones, thought to belong to a single stork, are between 20,000 to 50,000 years old, having been found in sediments dating to that age.
The giant bird is the latest extreme-sized species to be discovered once living on the island, which was home to dwarf elephants, giant rats and out-sized lizards, as well as humans of small stature.
"I noticed the giant stork bones for the first time in Jakarta, as they stood out from the rest of the smaller bird bones. Finding large birds of prey is common on islands, but I wasn't expecting to find a giant marabou stork," Dr Meijer told the BBC.
Only fragments of wing bones were found, but the researchers suspect the giant stork rarely, if at all, took flight.
Instead, the size and weight of its leg bones, and the thickness of the bone walls, suggest that the now extinct stork was so heavy that it lived most of its life on the ground.
It is thought to have evolved from flying storks that colonised the relatively isolated island.
Map showing the location of the Liang Bua caves on the island of Flores
"Flores has never been connected to mainland Asia and has always been isolated from surrounding islands. This isolation has played a key role in shaping the evolution of the Flores fauna," says Dr Meijer.
Many species on the islands evolved into either giants or dwarfs.
This phenomenon is known as the "island factor", and is thought to have been triggered by few mammalian predators being on the island. That led to abundant prey species becoming smaller, and other predators becoming larger.
"Larger mammals, such as elephants and primates, show a distinct decrease in size, whereas the smaller mammals such as rodents, and birds, have increased in size," explains Dr Meijer.
Among the giants evolved the giant stork, and the giant rat, Papagomys armandvillei, as well as Komodo dragons, the largest surviving species of lizard.
Dwarf species included the dwarfed elephant, Stedgodon florensis insularis, and the human species , popularly known as the 'hobbit' H. floresiensis.
Indeed, the remains of the giant stork were found in the same section of cave as the remains of H. floresiensis.
Discovered in 2004, H. floresiensis is thought to be a new human-like species standing just 1m tall, which survived until around 17,000 years ago.
It is thought to be descended from a prehistoric species of human - perhaps H. erectus - which reached island South-East Asia more than a million years ago.
"The status of this human contemporary has been subject of intense debate since its discovery," says Dr Meijer. "But in my opinion, the associated fauna is crucial in understanding the evolution of H. floresiensis."
The distinct difference in size between the 1.8 m-tall giant stork L. robustus and 1m-tall the tiny hominin H. floresiensis raises some interesting questions.
Would the hominin have eaten the giant stork?
Direct evidence of H. floresiensis 's diet is hard to come by, but it is suspected of hunting animals on the island for meat.
However, modern marabou storks mainly eat carrion, but they do take fish, frogs, and small mammals and birds.
So would the giant stork have eaten the hominin?
A modern, smaller marabou stork (Leptoptilos crumeniferus)
"Whether or not this animal may have eaten hobbits is speculative: there is no evidence for that," Dr Meijer told the BBC.
"But can not be excluded either."
The giant storks towered over the hobbits.
More importantly, juvenile hobbits were no bigger than giant rats that existed on the island, which themselves may have fallen prey to the giant stork, she adds.
As yet is it unclear why the giant stork, and the pygmy elephants and hobbit hominins, went extinct.
"But we have several clues," says Dr Meijer.
"All the bones of the giant marabou as well as those of the pygmy elephants and the hobbits are found below a thick layer of volcanic ash," suggesting a recent volcanic eruption.
"Second, the giant marabou and its contemporaries go extinct right before modern humans appear at the cave."
Around 15,000 years ago, the climate of Flores went from dry to being wetter, and a combination of any of these factors may have been enough to drive species on the islands to extinction.