Cannibalism: A Perfectly Natural History

The topic of dinosaur cannibalism is often debated, with evidence often inconclusive or misinterpreted. One of the earliest claims came in 1947 when paleontologist Edwin Colbert examined coelophysis bauri fossils from a mass grave in New Mexico. He believed that the stomach cavities contained juvenile coelophysis bones, concluding that these dinosaurs engaged in cannibalism. However, a 2005 study led by Sterling Nesbitt and Mark Norell at the American Museum of Natural History (AMNH) disproved this claim. Their analysis revealed that the supposed juvenile bones were from prehistoric crocodile relatives.

Another case emerged in 1998 when paleontologist Aase Jacobsen suggested that bite marks on Tyrannosaurus rex bones from Alberta, Canada, were evidence of cannibalism. However, Nesbitt and Norell challenged this, noting that the site contained two different tyrannosaur species, gorgosaurus and daspletosaurus. Since cannibalism requires conspecifics (members of the same species), they concluded that cannibalism in dinosaurs was “not as prevalent as was once supposed” (71).

In 2010, researcher Nicholas Longrich and his team found bite marks on tyrannosaurus rex fossils that matched Tyrannosaurus rex dentition, suggesting scavenging of carcasses by their own species. While Longrich argued that Tyrannosaurus rex engaged in cannibalism, Norell was skeptical, noting that the gouges could have resulted from intraspecific fights rather than feeding. The strongest evidence for dinosaur cannibalism, Norell claims, comes from Majungasaurus crenatissimus, a late Cretaceous theropod found in Madagascar. Geologist Raymond Rogers discovered numerous Majungasaurus crenatissimus bones bearing tooth marks identical to those of the species. He ruled out other large predators and determined that the bite marks were made during “late stage scavenging” (74) rather than combat, as they appeared on areas like the vertebrae that were only targeted to extract the last remaining nutrition from the carcass.

The debate highlights “two contrasting issues” (76). Some paleontologists believe that, given the prevalence of cannibalism in modern animals, it likely occurred in dinosaurs. Others, like Norell, argue that without direct fossil evidence—such as a dinosaur found with another of its species in its stomach cavity—cannibalism remains speculative. The fossil record is limited, making definitive conclusions difficult. Rogers noted that the term “cannibalism” garners significant media attention. While his original research referred to Majungasaurus crenatissimus as engaging in “conspecific scavenging” (77), it gained little notice until he rebranded it as cannibalism, demonstrating how certain terms captivate public interest, even when the science remains uncertain.

The definition of cannibalism can be ambiguous, particularly when considering behaviors like eating fingernails, mucus, or even breastfeeding. One unusual example of parental care that blurs the line between nourishment and cannibalism is found in caecilians, a group of “not very obvious” (78) legless amphibians that resemble worms or snakes. These secretive creatures inhabit tropical regions and display remarkable reproductive diversity, with some species laying eggs (oviparous) and others giving birth to live young (viviparous).

In viviparous caecilians, scientist Marvalee Wake discovered a unique feeding behavior. Studying fetal individuals, she noted that their temporary teeth differed from adult teeth, resembling “grappling hooks” (80). She also observed that the inner lining of the mother’s oviduct changed throughout pregnancy, thickening and producing a fat-rich secretion known as “uterine milk” (80). Upon closer examination, she proposed that fetal caecilians used their specialized teeth to scrape and consume this lining before birth. This behavior, though technically parental care, involved consuming the mother’s tissue, bringing it “into the realm of cannibalism” (81).

In egg-laying caecilians, researchers Alexander Kupfer and Mark Wilkinson made an even more startling discovery. Studying Boulengerula taitanus, they observed that newly hatched young used their teeth to strip and eat the outermost layer of their mother’s skin in a process called dermatophagy. Unlike typical skin, this outer layer was rich in fats, serving as the sole food source for the young for several weeks. Remarkably, the mother’s skin regenerated quickly, ensuring a continuous supply of nutrition. Scientists believe dermatophagy evolved first in egg-laying caecilians before being adapted by live-bearing species. In both cases, young caecilians developed specialized teeth that allowed them to consume maternal tissue to “fatten up” (83), highlighting an extreme form of parental investment that borders between nourishment and cannibalism.

In 1856, workers in a German limestone quarry uncovered unusual human-like bones, which were initially mistaken for a bear’s remains. Anatomist Hermann Schaaffhausen identified them as belonging to a “primitive” (85) human, later named Neanderthal Man after the Neander River Valley. However, the scientific community, still entrenched in creationist beliefs, dismissed the discovery, attributing the skeletal features to disease rather than evolutionary significance.

By the 1860s, Darwin’s On the Origin of Species had sparked interest in human evolution. Scientists like Thomas Huxley championed Neanderthals as evidence of gradual evolutionary change. However, in 1911, anthropologist Marcellin Boule reconstructed a Neanderthal skeleton with a slouched posture, depicting them as primitive and unintelligent. This misconception persisted for decades, influencing popular culture and leading to Neanderthals becoming “poster boys for stupidity and bad behavior” (87).

Two competing hypotheses emerged about Neanderthal-human relations. The Regional Continuity Hypothesis, supported by Milford Wolpoff, posited that Neanderthals interbred with early Homo sapiens, gradually evolving into modern humans. In contrast, the Out of Africa Hypothesis, championed by Ian Tattersall, argued that modern humans originated in Africa and displaced, rather than interbred with, Neanderthals. Neanderthals, scientist Ian Tattersall says, were “incredibly different” (89). Recent genetic and morphological studies support the latter, showing minimal Neanderthal ancestry in modern humans.

Neanderthals were highly intelligent—using tools, fire, and clothing—and had larger brains than modern humans. Evidence of Neanderthal cannibalism was debated for years, with early claims proving inconclusive. However, sites in Spain, France, and Croatia revealed bones with butchery marks consistent with “patterns of processing” (91), suggesting Neanderthals occasionally practiced cannibalism. The discovery at Moula-Guercy, France, was particularly compelling, as Neanderthal remains were found alongside butchered animal bones, processed in the same manner.

Despite such evidence, distinguishing between cannibalism and “non-cannibalistic mortuary practices” (93) remains challenging. Secondary burials, ritualistic cutting, and environmental factors can alter skeletal remains, complicating interpretations. A controversial discovery at Cowboy Wash, Colorado, included fossilized feces containing human myoglobin, suggesting cannibalism among prehistoric Puebloans. However, skeptics argue the remains could have been scavenged by animals. In Spain’s Atapuerca region, Homo antecessor, a potential ancestor of Neanderthals, exhibited clear evidence of cannibalism, with butchered human bones found alongside animal remains. Unlike survival-driven cannibalism, this behavior may have been habitual. They may have “eaten human flesh because it was readily available and because they liked it” (97). Ultimately, Neanderthals likely vanished around 30,000 years ago, possibly outcompeted or eliminated by modern humans. Ian Tattersall suggests that as Homo sapiens developed symbolic thought, they became superior competitors, leading to the Neanderthals’ extinction.