Legend of the Killer Storks

What makes a monster? Godzilla, Medusa, Frankenstein’s monster, Fáfnir, the Alien: All these fictional fiends have disparate origins, attributes, and motivations, but they are tied together by their disregard for what we perceive as the natural order. Each is an aberrant creation — something from an earlier age, or something corrupted — that disrupts the harmonious arrangement of the universe. They are not just frightening. The tiger stalking in the jungle and the crocodile lurking in the shallows can inspire terror, but monsters are ominous beings which question the rules of existence as we know it.

There is no natural category of monstrous things. Stephen Asma, in his appropriately titled On Monsters, writes “The monster, of course, is a product of and a regular inhabitant of the imagination, but the imagination is a driving force behind our entire perception of the world. If we find monsters in our world, it is sometimes because they are really there and sometimes because we have brought them with us.” Even the ordinary can be a wellspring for monsters. Consider the plight of Scott Carey (played by Grant Williams) in 1957’s The Incredible Shrinking Man. Reduced to Lilliputian size by a mix of hydrogen gas and pesticide, housecats and ordinary spiders suddenly become fearsome giants. This situation is reversed in the formicid films Them! (1954) and Empire of the Ants (1977). Exposed to the dangerous chemical output of our industry, ordinary ants attain enormous size and attempt to claim the world for themselves.

These creature features are modern tales invented since our species has appointed itself to a position of dominance over nature — part of the point of these “revenge of nature” films is to remind us that our control is not as complete as we might believe — but it has only been recently that we have been able to develop such a conceit. Since the origin of the first humans over 6 million years ago, our kind has been prey. Many of the world’s famous fossil human deposits, from the collection of Homo erectus bones at China’s Dragon Bone Hillthe collection of Homo erectus bones at China’s Dragon Bone Hillthe collection of Homo erectus bones at China’s Dragon Bone Hill to the “First Family” of Australopithecus afarensis in Ethiopia, were created by predators. It is here, among the ranks of prehistoric predators, where science and science fiction intersect. On one peculiar Indonesian island, giant birds may have frightened some of our evolutionary cousins.

Fossil birds don’t often receive good press. Numerous papers pass through the academic literature each year without even a nod from journalists, but the description of a prehistoric stork on the island of Flores proffered such delicious headline bait that reporters could not resist. Although no bigger than its modern-day relatives, this 6-foot stork would have towered over the tiny Flores “hobbits” — a strange lineage of humans that became dwarfed during their tenure on the island. That the stork killed and consumed the humans seemed a foregone conclusion. “Giant stork ‘preyed on Flores hobbits’” said Britain’s Telegraph, while the Independent went with the cheekier title “Stork that ate babies, rather than delivering them” and the cesspool of shoddy journalism that is the Daily Mail crowed “Revealed: The giant stork that used to terrorise Indonesia’s tiny ‘hobbits.’” The Toronto Star even went a step further to rhetorically ask “Were ‘hobbit’ humans killed off by giant storks?”, implying that the disappearance of the unique Flores people were attributable to the big birds.

The coexistence of tiny humans and huge birds was the perfect setup for a new monstrous tale worthy of Hollywood. (In fact, a film about giant, rapacious birds based upon the pulp novel The Flock may be in the works.)  The island of Flores, thought to lack any sizable mammalian carnivore during the time of the hobbits, suddenly gained a predator which would have towered over the resident humans. Yet, in an occurrence frustratingly common in modern science journalism, the hyperbolic claims quickly outpaced the actual evidence and obscured the actual significance of the discovery. In order to comprehend the unique nature of these birds, we first have to understand their island neighbors and how the strange assemblage of creatures on Flores came together.

What is currently known about the hobbits and the animals they lived alongside primarily comes from a site called Liang Bua cave. Early excavations of the cave were carried out in 1965 by the local missionary and amateur archaeologist named Theodor Verhoeven. He mostly found the remains of recent Neolithic people who had been ceremonially buried with bronze axes and other goods, but he also uncovered traces of an even older culture (which he had found elsewhere on Flores and took to indicate that Homo erectus had made it to the island). Other archaeologists investigated the cave since that time, but it was only in 2001 that a team organized by Michael Morwood dug down deep into the cave to search for traces of the older Pleistocene-age fossils and artifacts that Verhoeven’s documentation showed were present.

The most famous Flores inhabitants were the hobbits. For most of the past 150 years, human evolution has been depicted as proceeding along a linear path from an ape ancestor to Homo sapiens. Anthropologists haggled over the relationship of Neanderthals to us — ancestor? cousin? throwback? — and the proper place of the australopithecines, but within the last thirty years an increasingly complex and bushy picture. Multiple species of human lived alongside one another at any one time and recent genetic studies have made a good argument for interbreeding between distinct populations of prehistoric humans during the past 50,000 years.

Where the hobbits fit into this picture is a matter of dispute. These people were small, standing a little more than 3 feet tall as adults, and their skeletons were mosaics of traits seen among earlier humans and more recent species. These strange characteristics have led some anthropologists to cast them as pathological individuals of modern humans, but others have made a strong case that they are a unique species of dwarfed humans given the name Homo floresiensis. In this latter case, these minuscule humans would have been derived from an ancestral population of Homo erectus — or an as-yet-unknown intermediate species — which became dwarfed on the island of Flores around 94,000 years ago before disappearing as recently as 18,000 years ago.

Homo floresiensis is the first known species of human to have become dwarfed — running counter to the ubiquitous onward-and-upward imagery of human evolution — but this phenomenon has been seen among other prehistoric vertebrates, too. In Transylvania paleontologists have found the vestiges of a 70-million-year-old island that was home to dwarf hadrosaurs (Telmatosaurus) and sauropods (Magyarosaurus) which may have been preyed upon by odd raptor dinosaurs with double sickle claws on their feet (Balaur). Even more recently, about 47,000 years ago, a population of Columbian mammoths (Mammuthus columbi) became stranded on what is now California’s Santa Rosa Island. They, too, became dwarfed, and are known as a unique species Mammuthus exilis. In fact, prehistoric elephants seemed especially prone to dwarfing — there were dwarf woolly mammoths as recently as 4,000 years ago on Wrangel Island off the northern coast of Siberia, and even Flores had its own dwarf species of the extinct elephant Stegodon.

Much like the Hateg dinosaurs and the mammoths of Santa Rosa, the hobbits and Stegodon of Flores were products of the “Island Effect” (also called Foster’s rule for the scientist who first identified the trend, rather than the Australian beer). For reasons not yet fully understood, large species which become isolated on islands often become dwarfed while smaller species increase in size over time. These changes are probably not attributable to any single cause, but rather to an array of pressures involving competition for resources and the absence of large carnivores which affect species in different ways.

The elephants and hobbits were not the only Flores inhabitants to have originated in isolation. Almost every species which lived on the island during the time of the hobbits was unusual. As recently reviewed by Netherlands Centre for Biodiversity Naturalis scientist Hanneke Meijer and colleagues, the hobbits lived alongside the small elephant Stegodon florensis insularis; the giant rats Papagomys armandvillei, Papagomys theodorverhoeveni, and Spelaeomys florensis; Komodo dragons (Varanus komodoensis); and the newly-described cousin of the modern Marabou stork. While traces of the hobbits go back only about 94,000 years, many of the fossil mammals correspond to an even earlier fossil site on the island at Mata Menge dating to 800,000 years ago, indicating that many of the species found at Liang Bua had been on the island for at least three-quarters of a million years.

The correspondence between the older and the younger Flores sites is significant because it shows that there few, if any, new arrivals to the island during the intervening time. This helps to explain the relatively low species diversity on Flores, and accords with the idea that the island was probably difficult to reach. The Flores fauna was not exactly like that found elsewhere. The animals present on Flores were those capable of reaching the island, and so the fauna represents an assemblage of animals which was cobbled together from various species which were capable of crossing the ocean barriers. Once they arrived, they changed in isolation, but they were also vulnerable to extinction. Both the hobbits and the Stegodon species became extinct between 19,000 and 18,000 years ago, a date which coincides with a volcanic eruption (which did not disrupt the persistence of the rodent species on the island).

The newly-described giant stork was one of the animals changed by the unique island habitat. Represented by part of the left forearm (ulna), the fused wrist and knuckles (carpometacarpus), part of a mid-leg bone (tibiotarsus), and the left femur, there was enough characteristic material to identify the bird as a distinct relative of the living Marabou stork (Leptoptilos crumeniferus). To a 3-foot-tall hobbit — about the same size as their distant australopithecine forebears — the 6-foot stork would have been huge, but in truth this bird was not much larger than its close relatives. Named Leptoptilos robustus by Meijer and Rokus Awe Due of Indonesia’s National Centre for Archaeology, this fossil stork was comparable in size to the modern Great Adjutant (Leptoptilos dubius) and the 6-foot fossil stork Leptoptilos falconeri, the latter of which ranged widely from Asia to Africa and Europe 5 to 2½ million years ago. The Flores stork was a big bird, there is no question about that, but it is not representative of island gigantism. Instead, Leptoptilos robustus became adapted in a different way.

Considerations about the origin of birds are closely tied to questions about the origin of flight. The development of the flight-stroke and powered flight have traditionally been key factors in determining what makes a bird (although, as we find more avian traits among dinosaurs, it is becoming increasingly difficult to define what a bird is). Yet, no sooner did birds start flying than some lineages began to lose that ability. The well-known toothed bird Hesperornis from the Cretaceous chalk of Kansas — one of the 19th-century fossil hunter O.C. Marsh’s prize discoveries — had only tiny nubbins of bones for its forelimbs and lived a mostly aquatic life darting after fish in the long-gone Western Interior Seaway. The ratites — a group containing everything from the extinct moas to the strange Kiwi of New Zealand — represent another famous flightless lineage, as do the penguins on the extinct “terror birds” (properly known as the phorusrhacids) of South America. Looking at it from a wide perspective, the loss of the ability to fly is a relatively common occurrence among birds, and Leptoptilos robustus appears to represent yet another case.

Although it was about the same size as other storks, the walls of bone in the lower leg of the Flores stork were about twice as thick as those in the Great Adjutant and most closely approached the condition seen in the extinct species Leptoptilos siwalicensis from the Pliocene of India. Given the size and thickness of this bone, Meijer and Due have restored the Flores stork as a tall, but stout, bird. In terms of height it would have been about 6 feet tall, but the thickness of its leg bones indicate that it was probably much heavier — approximately 16 kilograms [35 pounds] by the estimation of Meijer and Due, making it almost twice as hefty as even the largest living stork. If this is correct, would the Flores stork have been able to fly?

Lacking the complete forelimbs of the Leptoptilos robustus, we cannot know the size of its wingspan or model its flight capabilities. Based upon the size of the bird and the thickness of its lower limb bones, however, it appears that this bird would have been significantly heavier than storks of comparable size. This runs contrary to what would be expected in a flying bird in which reduced weight and thin-walled bones would be expected. Perhaps this stork spent most of its time on the ground. As Meijer and Due state, “A lifestyle with a reduced ability for flight and a greater reliance on terrestrial locomotion would subject a bone to such mechanical loading” and therefore cause the evolution of such thick bones.

This reconstruction of the Flores stork — as a primarily ground-dwelling bird which may not have been able to fly — is indicative of just how strange the island’s fauna was. Clearly the ancestors of L. robustus would have flown to the island, and so the peculiar anatomy of this newly-described stork evolved on Flores as a result of isolation. (What species it evolved from is difficult to determine from the scanty record of fossil storks in Asia. The wide-ranging species L. falconeri would seem to be a good candidate, Meijer and Due write, but it disappeared about 2½ million years before the Flores stork and therefore must be ruled out.) The bird did not become dwarfed like the hominins or the elephants, but instead became adapted into a unique, mainly terrestrial form.

The reason why the Flores stork became adapted to life on the ground might be found in the island’s unique menu. Giant storks are well-known consumers of carrion and are frequent attendees at carnivore kills, garbage dumps, and other places where meat may easily be obtained. Today these birds compete with many other scavengers, including carnivores which raid each other’s kills, but on Flores there were no large carnivorous mammals. There were Komodo dragons, but not the array of carnivorans found elsewhere. Given this lack of large predators and the abundance of large rats, Flores would have been paradise for a meat-eating bird, and this may have given a selective advantage for heavier birds with sturdier legs. This kind of selective pressure may very well have led to the origin of L. robustus, although there would have been a cost. If the Flores stork lost its ability to fly and was endemic to the island it evolved on, it would not have been able to escape.

Thanks to a few bones, Meijer and Due have identified a strange new bird which became uniquely adapted to life on the ground, but was L. robustus truly a threat to the island’s hobbit population? We honestly don’t know. As is often the case with media-mangled science stories, the degree to which a story is hyped is inversely proportional to the weight of the conclusions drawn from the research in question. In this case, Meijer and Due did not mention the hobbits as prey for the stork at all. There is not a single shred of hard evidence that the bird killed or consumed hobbits, and, to the credit of Meijer, she repeatedly told reporters this. Quoted in the Daily Mail’s article, for instance, Meijer stated “Whether or not [L. robustus] may have eaten hobbits is speculative: there is no evidence for that.” The lure of a tasty headline is difficult to resist, however, so it is no wonder that the headlines reconstructed the Flores stork as a horrific bird akin to the man-eating Giant Claw or the terror birds of the more recent 10,000 B.C.

Yet, lest I dispatch the idea of human-eating storks as a case of media fluff, the Flores stork certainly would have been a formidable predator of small mammals and it is not inconceivable that L. robustus could have consumed young hobbits (or even scavenged dead adults). There is no positive evidence for predation, but we should not be so hasty as to rule out the possibility altogether, especially since small humans in other places and at other times were killed and consumed by birds of less imposing stature.

While teaching anatomy at the University of the Witwatersand in Johannesburg in 1924, the Australian scientist Raymond Dart was informed that fossil primate remains — particularly skulls — were being found at a local limestone quarry. Dart was extremely excited to hear this. Fossil primates are exceptionally rare, and he arranged for a few crates of fossil-bearing rock to be delivered to his home. When they arrived, Dart found the skull of a juvenile hominin — a prehistoric human he named Australopithecus africanus the following year in Nature.

The juvenile status of the Taung child, as it was popularly known, was recognized from the time of its description. In fact, it was this understanding that allowed many paleoanthropologists to cast aspersions about its pedigree. The skulls of juvenile apes shared similarities with our own which disappeared as they grew, so Australopithecus africanus was marginalized as a human-like ape until the anthropologist W.E. le Gros Clark reanalyzed the fossils in the 1950s and brought the australopithecines into the human family. What many researchers had missed, however, was the pattern of scratches and broken bone seen around the eyes and back of the child’s skull.

The Taung child was not a hapless kid buried in a flood or mudslide. The unfortunate A. africanus child fell victim to a large bird of prey, just as many monkeys do today. In a 2006 issue of the American Journal of Physical Anthropology the anthropologist Lee Berger took a cue from a study of bones accumulated by crowned hawk eagles — particularly primate skulls — to reexamine damage he and R.J. Clarke had detected on the Taung skull a decade earlier. The hypothesis was originally based upon damage done to the outside of the skull, but, after seeing the patterns of damage done by raptors to modern monkey skulls, Berger was able to find similar punctures and scratches inside the eye sockets of the australopithecine child.

The fact that the Taung child was killed and eaten by a bird of prey is obviously not proof that the Flores stork captured and consumed hobbits. I mention it here because it is representative of a more general point — not only were humans prey during prehistory, but were small enough that they could have been relatively easy pickings for a variety of carnivorous animals, including birds. In the case of the hobbits, they would not have had to fear the large carnivores which fed on hominins elsewhere, such as the giant hyenas which created the unique assemblage of bones at China’s Dragon Bone Hill. As has been the case with many other insular island faunas cobbled together from species able to cross channels and stretches of sea, carnivores were absent. This is what allowed the unique character of the Flores fauna to evolve, including a large, carnivorous, ground-dwelling bird. There is no positive evidence that the Flores stork ate humans, but neither is it outside the realm of possibility, and we must await further evidence.

Regardless of whether or not the Flores stork hunted hobbits, its discovery adds another aspect to an already unusual assemblage of animals. In the absence of other dominant predators, a bird with an undiscriminating palate became specialized, and, perhaps, was ultimately trapped on the island where it evolved. In its own way, it made a common avian reversal by coming down to the ground to become one of the island’s dominant predators. Perhaps, to the hobbits, it was truly a monstrous bird, but we should be careful about allowing it to roost in such a shadowy part of our imagination.

The prospect of an upside down world — in which tiny humans fled giant, bloodthirsty storks — is so compelling that the spate of hyped news reports is not at all surprising. The Flores stork was just the latest creature to be added to the menagerie of monstrous prehistoric creatures that enthrall us. As David Quammen concluded in Monster of God, “Such creatures enliven our fondest nightmares. They thrill us horribly…. They allow us to recollect our limitations. They keep us company…. If we exterminate the last magnificently scary beats on planet Earth, as we seem bent upon doing, then no matter where we go for the rest of our history as a species — for the rest of time — we may never encounter any others.”

We live in a world depauperate of monsters. Especially from a Western, 21st-century perspective, there are no wild monsters left. We have killed ours, and exotic beasts that still frighten people in poorer, less-developed parts of the world — such as those described by Quammen — have been ensconced in zoos; not tame, but no longer threatening. (How many parents take their children up to lion, leopard, and tiger enclosures and say “Look at the big kitties!”) Prehistory is one of the few places where we can find monsters and let our imaginations run wild. From Tyrannosaurus rex to Leptoptilus robustus, these long-lost predators seem monstrous. The thought of bringing them back to life — through science or science fiction — creates imaginary perils that we find delightfully frightening (no matter how realistic the restoration, we are safe, separated by thousands or millions of years from those teeth and claws). But such hyperbole may blind us to the intricacy and wonder of how such a bizarre creature came to exist in the first place.

UPDATE: Reader Paul Threatt has sent me an alternate hypothesis about the relationship between the Flores storks and the hobbits. Perhaps the prodigious birds were more relevant to human evolution than might be initially supposed…

Top Image: Flickr/Freddie H

References:

Berger, L. (1995). “Eagle involvement in accumulation of the Taung child fauna” Journal of Human Evolution, 29 (3), 275-299 DOI: 10.1006/jhev.1995.1060

Berger, L. (2006). Brief communication: “Predatory bird damage to the Taung type-skull of Australopithecus africanus Dart 1925″ American Journal of Physical Anthropology, 131 (2), 166-168 DOI: 10.1002/ajpa.20415

Meijer, H., & Due, R. (2010). “A new species of giant marabou stork (Aves: Ciconiiformes) from the Pleistocene of Liang Bua, Flores (Indonesia)” Zoological Journal of the Linnean Society, 160 (4), 707-724 DOI: 10.1111/j.1096-3642.2010.00616.x

Meijer, H., Van Den Hoek Ostende, L., Van Den Bergh, G., & De Vos, J. (2010). “The fellowship of the hobbit: The fauna surrounding Homo floresiensis” Journal of Biogeography, 37 (6), 995-1006 DOI: 10.1111/j.1365-2699.2010.02308.x