Cannibalism

by Bill Schutt

So was dinosaur cannibalism a rare event? There appear to be two contrasting issues here. First, knowing what we do about the prevalence of cannibalism in the animal kingdom, it makes sense that dinosaurs might have exhibited the behavior for the same reasons other animals do—namely overcrowding, predation, competition, and hunger. Alternately, cannibalism is relatively rare in birds, the only surviving link to the Mesozoic dinosaurs. The problem with comparing the two groups, though, is that birds are gape-limited predators while carnivorous dinosaurs certainly were not.

  Then there’s the lack of widespread physical evidence that dinosaur cannibalism occurred, and because of this, some paleontologists, like Mark Norell and his colleagues, are unwilling to make any sort of speculative leap. Instead their explanations for the strange bite marks on ancient T. rex bones fall back onto behavior they do have evidence for—like fighting. According to Norell, “There’s nothing like a smoking gun that anyone has ever presented to me and said, ‘This is it!’ ”

  “Can you give me an example of a paleontological ‘this is it’ moment?” I asked.

  Norell brought up the now-generally-accepted claim that modern birds were actually theropod dinosaurs and would, therefore, show similar anatomical and behavior traits.

  “We found evidence that dinosaurs sat on their nests,” he said. “We were able to show that. Dinosaur feathers—we were able to show that. In our lab we tend to be incredibly careful about what we say about this stuff . . . but no one has ever been able to come up with a total case for dinosaur cannibalism, like a member of the same species that’s inside the body cavity. Like Coelophysis was supposed to be.”

  In a telling side story, Raymond Rogers provided another example of just how attractive the word cannibalism is to the media. “I took this story of dinosaur cannibalism to the Society of Vertebrate Paleontology meetings, and I called it “Conspecific Scavenging,” which is what I think it is. I remember that a guy from Science News looked at it, but nobody else really took much notice at all. I went home and thought about it, and I was like, ‘You know, why don’t I just call it cannibalism?’ So I did . . . and after that the story got in Nature and it was on the front page of Google News for about a week.”

  “Well there you go,” I responded with a laugh. “That word does set something off in us.”

  “Right,” Rogers agreed. “Before I knew it, USA Today was talking about dinosaurs, chianti, and fava beans.”

  7: File Under: Weird

  Cannibalism is found in over 1,500 species. Anthropophagusphobia (fear of cannibals) is found in only one. Which seems unnatural now?

  — Author unknown

  Is eating one’s own fingernails or mucus an example of auto-cannibalism? And what about breast-feeding? Is this type of parental care actually a form of cannibalism? Raymond Rogers considers scavenging the body of a conspecific dinosaur a form of cannibalism. Mark Norell, not so much. All are examples of a gray area between what most people consider cannibalism and other forms of behavior.

  Like breast-feeding, the following example is a form of parental care, but one that extends further into the realm of cannibalism-related behavior. It occurs in the caecilians, a small order of not-very-obvious amphibians, whose legless bodies often get them mistaken for worms or snakes. Caecilians inhabit tropical regions of Central and South America, Africa, and Southern Asia—a neat trick that definitely lends support to the theory of continental drift. Although some caecilians are aquatic, it is not believed that their ancestors were strong enough swimmers to cross the Atlantic Ocean. Instead, prehistoric caecilians were likely separated when the current continents of South America and Africa split apart between 100 and 130 million years ago.

  Caecilians also serve as great examples of convergent evolution, in which unrelated organisms each evolve similar anatomical, physiological, or behavioral characteristics, because they inhabit similar environments. As a result of their subterranean lifestyles, caecilians share a number of anatomical similarities with moles and mole rats. In each, the eyes are either set deeply into the skulls or are covered by a thick layer of skin, and as a consequence they are nearly blind.

  Caecilians also possess a pair of short “tentacles” located between their nostrils and eyes. These chemosensors enable the subterraneans to “taste” their environments without opening their mouths, as they burrow through the soil or leaf litter in search of insects and small vertebrates. Similar types of sensory structures can be seen in other burrowing creatures, most notably the aptly named star-nosed mole (Condylura cristata).

  As a group, caecilians exhibit a fair degree of reproductive diversity (which will become an important aspect of their cannibal-related behavior). Approximately half of the 170 species are oviparous (egg layers), and hatchlings either resemble miniature versions of their parents or pass through a brief larval stage. Other species are viviparous, giving birth to tiny, helpless young.

  All caecilians do share one characteristic unique to the amphibians: internal fertilization, and during this process, sperm is deposited into the female’s cloaca with the aid of a penis-like structure called a phallodeum. For the orifice-challenged, a reminder that in many vertebrates (like amphibians, birds, and reptiles), the cloaca is a single opening shared by the intestinal, reproductive, and urinary tracts.

  But as interesting as the concept of legless caecilians wielding their penises underground might be (admittedly, it disturbed some of my older Italian relatives until I explained the spelling differences), information about caecilian cannibalism began emerging from Marvalee Wake’s lab at the University of California, Berkeley. The herpetologist extraordinaire was looking at fetal and newborn individuals from several viviparous species and began investigating the function of their peculiar-looking baby teeth (better known to scientist-types as deciduous dentition).

  While some of the teeth were spoon-shaped, others were pronged or resembled grappling hooks, but none of them resembled adult teeth. Wake also performed a microscopic comparison of caecilian oviducts. She observed that in pregnant individuals, the inner (i.e., epithelial) lining of the oviduct was thicker and had a proliferation of glands, which she referred to as “secretory beds.” These glands released a substance that fellow researcher H.W. Parker had previously labeled “uterine milk.” Parker described the goo, which he believed the fetuses were ingesting, as “a thick white creamy material, consisting mainly of an emulsion of fat droplets, together with disorganized cellular material.” He also thought that the caecilians’ fetal teeth were only used after birth, as a way to scrape algae from rocks and leaves. Wake, however, had her doubts, especially since she noticed that these teeth were resorbed before birth or shortly after.

  Pressing on with her study, Wake saw something odd. In sections of oviduct adjacent to early-term fetuses, the epithelial lining was intact and crowded with glands. However, in females carrying late-term fetuses, the lining of the oviduct was completely missing in the areas adjacent to the fetuses, although it was intact in regions well away from the action. Wake proposed that fetal caecilians used their teeth before birth to scrape fat-rich secretions and cellular material from the lining of their mother’s oviduct. Although this behavior couldn’t be seen directly, she had gathered circumstantial evidence in the form of differences in the oviduct between early-term and late-term individuals. After an analysis of fetal stomach contents revealed cellular material, Wake had enough evidence to conclude that caecilian parental care extended beyond the production of uterine milk and into the realm of cannibalism. Unborn caecilians were eating the lining of their mothers’ reproductive tracts.

  But if the consumption of maternal epithelial cells in viviparous caecilians gave this admittedly strange behavior a cannibalistic slant, it was in the egg-laying species that the story really took off.

  In 2006, caecilian experts Alexander Kupfer, Mark Wilkinson, and their coworkers were studying the oviparous African caecilian, Boulengerula taitanus, when they made a remarkable discovery. This species had be
en previously reported to guard its young after hatching, and the researchers wanted to examine this behavior in greater detail. They collected 21 females and their hatchlings and set them up in small plastic boxes designed to resemble the nests they had observed in the field. Their initial observations included the fact that the mothers’ skin was much paler than it was in non-moms and that hatchlings had a full set of deciduous teeth resembling those employed by their oviduct-munching cousins.

  Intrigued, the researchers set out to film the parental care that had been briefly described by previous workers. On multiple occasions, Kupfer and Wilkinson observed a female sitting motionless while the newly hatched brood (consisting of between two and nine young) slithered energetically over her body. Looking closer, they noticed that the babies were pressing their heads against the female, then pulling away with her skin clamped tightly between their jaws. As the researchers watched, the baby caecilians peeled the outer layer of their mother’s skin like a grape . . . and then they consumed it.

  Scientists now know that these bouts of “dermatophagy” reoccur on a regular basis and that the mothers’ epidermis serves as the young caecilians’ sole source of nutrition for up to several weeks. For their part, female caecilians are able to endure multiple peelings because their skin grows back at a rapid rate.

  “The outer layer is what they eat,” Wilkinson said. “When that’s peeled off, the layer below matures into the next meal.”

  In addition to the ability of the skin to quickly repair and replenish itself, the nutritional content of this material is yet another interesting feature in this bizarre form of parental care. Normally, the outermost epidermal layer, the stratum corneum, is composed of flattened and dead cells whose primary functions are protection and waterproofing. But when the researchers examined the skin of brooding female caecilians under the microscope, they noticed that the stratum corneum had undergone significant modification. Not only was the layer thicker, it was also heavily laden with fat-producing cells, which explained why the baby caecilians experienced significant increases in body length and mass during the weeklong observations. It also explained why mothers of newly hatched broods experienced a concurrent decrease in body mass of 14 percent. In short, dermatophagy is a great way to fatten up the kids, but for moms on the receiving end of their gruesome attentions, the price is steep.

  Scientists now believe that the presence of dermatophagy in both South American and African oviparous species offers strong support for the hypothesis that these odd forms of maternal investment originally evolved in the egg-laying ancestor of all modern caecilian species. Consequently, when the first live-bearing caecilians evolved, their unborn young were already equipped with a set of fetal teeth, which took on a new function, allowing them to tear away and consume the lining of their mothers’ oviduct.

  8: Neanderthals and the Guys in the Other Valley

  Here is a pile of bones of primeval man and beast all mixed together, with no more damning evidence that the man ate the bears than that the bears ate the man—yet paleontology holds a coroner’s inquest in the fifth geologic period on an ‘unpleasantness’ which transpired in the quaternary, and calmly lays it on the MAN, and then adds to it what purports to be evidence of CANNIBALISM. I ask the candid reader, Does not this look like taking advantage of a gentleman who has been dead two million years.

  — Mark Twain, Life As I Find It, 1871

  In 1856, three years before publication of Charles Darwin’s On the Origin of Species, a worker at a limestone quarry near Düsseldorf, Germany, uncovered the bones of what he thought was a bear. He gave the fossils to an amateur paleontologist, who in turn showed them to Dr. Hermann Schaaffhausen, an anatomy professor at the University of Bonn. The bones included fragments from a pelvis as well as arm and leg bones. There was also a skullcap—the section of the cranium above the bridge of the nose. The anatomist immediately knew that while the bones were thick and strongly built, they had belonged to a human and not a bear. They were, though, unlike any human bones he had ever seen. Beyond the robust nature of the limbs and pelvis, the skullcap had a low, receding forehead and a prominent ridge running across the brow. These anatomical differences led him to conclude that these were the remains of a “primitive” human, “one of the wild races of Northern Europe.”

  The next year, the men announced their discovery in a joint paper, but the excitement they hoped to generate never materialized. This was, after all, a scientific community that had yet to reject the concept that organisms had not changed since God created them only five thousand years earlier. It was no real surprise, then, when a leading pathologist of the day examined the bone fragments and pronounced them to be modern in origin, insisting that the differences in skeletal anatomy were pathological in nature, having been caused by rickets, a childhood bone disease. He blamed the specimen’s sloping forehead on a series of heavy blows to the head.

  By the early 1860s, thanks to the publication of On the Origin of Species, there was increased interest in evolution, especially the topic of human origins. Now the concept of “change over time” was no longer alien, and in the newly minted Age of Industry, the idea of the survival of the fittest was not only palatable, it was profitable. By 1864, the rickets/head injury hypothesis had been overshadowed by the discovery of new specimens with identical differences in skeletal structure. Neanderthal Man became the first prehistoric human to be given its own name, a moniker derived from the Neander River Valley, where the presumed first fossils had been uncovered.11

  Thrust into the scientific and public eye, Neanderthal Man became a Victorian era sensation. Scientists like Darwin’s contemporary and friend Thomas Huxley believed these particular remains were important because they established a fossil record for humans that supported Darwin’s newly published theory. With none of his friend’s famous restraint, Huxley announced that Homo sapiens had descended with modification from apelike ancestors, and the Neanderthals were just the proof he needed.

  Huxley’s rationale was that, although Neanderthals shared many characteristics with modern humans, they also exhibited primitive traits, thus serving as physical evidence that humans, like other organisms, had evolved gradually and over a vast time frame. Neanderthals, he reasoned, were a part of Darwin’s branching evolutionary tree, with this particular branch leading to modern humans.

  The most serious argument against Huxley’s hypothesis was put forth in 1911. Marcellin Pierre Boule, a French anthropologist and scientific heavyweight, had been called upon to study and reconstruct a Neanderthal specimen that had been uncovered in France several years earlier. Once Boule was finished, anyone viewing the reconstruction would come away with some strong ideas about what Neanderthals looked like. Significantly, he gave the skeleton a curved rather than upright spine, indicative of a stooped, slouching stance. With bent knees, flexed hips, and a head that jutted forward, Boule’s Neanderthal resembled an ape. The anthropologist also claimed that the creature possessed the intelligence (or lack of intelligence) to match its apelike body.

  Boule commissioned an artist to produce an illustration of his reconstruction, and the result depicted a hairy, gorillalike figure with a club in one hand and a boulder in the other. The creature stood in front of a nest of vegetation, another obvious reference to gorillas. Boule’s vision of Neanderthals, with their knuckle-dragging posture and apelike behavior, also left an indelible mark on a public eager to hear about its ancient ancestors. For decades to come, Neanderthals would become poster boys for stupidity and bad behavior. The epitome of a shambling, dimwitted brute, “Neanderthal” became synonymous with “bestial,” “brutal,” savage,” and “animal.”12 In “The Grisly Folk,” an influential story written by H. G. Wells in 1921, the author stuck to the Boule party line, depicting “Neandertalers” as cannibalistic ogres: “when his sons grew big enough to annoy him, the grisly man killed them or drove them off. If he killed them he may have eaten them.” According to Wells, the grisly men also developed a taste
for the modern humans who had moved into the neighborhood, finding “the little children of men fair game and pleasant eating.” Because of this type of rude behavior (“lurking” was also a popular activity), Wells felt that the ultimate extermination of the Neanderthals was completely justified, allowing modern humans to rightfully inherit the Earth.

  The only problem with Wells’s character, according to paleontologist Niles Eldridge, was that it was based on Boule’s misconceptions. “Every feature that Boule stressed in his analysis can be shown to have no basis in fact.”

  Since the early 20th century, Neanderthals have undergone a further series of transformations and today there are two main hypotheses.

  That they were our direct ancestors (Homo sapiens neanderthalensis) became part of what is known as the Regional Continuity hypothesis. It is a view currently supported by paleoanthropologist Milford Wolpoff, who believes that Neanderthals living in Europe and the Middle East interbred with other archaic humans, eventually evolving into Homo sapiens. According to Wolpoff, similar regional episodes took place elsewhere around the globe as other archaic populations intermingled, hybridizing into regional varieties and even subspecies of humans. Importantly, though, there would be enough intermittent contact between these groups (Asians and Europeans, for example) so that only a single species of humans existed at any given time.

  Alternatively, the Out of Africa hypothesis holds that modern humans evolved once, in Africa, before spreading to the rest of the world where they displaced, rather than interbred with, the Neanderthals (Homo neanderthalensis) and others who had been there previously. The groups driven to extinction by Homo sapiens had themselves evolved from an as-yet-undiscovered species of Homo (perhaps H. erectus) that had originated in Africa and migrated out earlier.

  I interviewed Ian Tattersall in his impressively cluttered office at the American Museum of Natural History, where he is curator emeritus in the Division of Anthropology. Tattersall is one of the world’s eminent paleoanthropologists and has authored (or coauthored) more than a hundred articles on ancient hominids, as well as popular books on the topic. He is a major proponent of the Out of Africa hypothesis.