Why Paleontologists Should Love Meat-Eaters

Let's face it: Carnivory isn’t for everyone. (Try taking a vegetarian to a steakhouse if you need further convincing.) But there is one case in which paleontologists agree that chewing flesh is an unassailable good: Meat-eaters helped make our remarkable fossil record.

Consider an unfortunate human known to experts as SK 54. We don’t know whether this young Paranthropus was happily skipping along or grumpily trudging through the veldt just before tragedy struck, but what we do know is that this prehistoric human became a leopard’s dinner. Two rounded punctures in the 1.5 million year old skull roof mark where a big cat dragged the youngster off by the head, the big cat’s interpretation of getting take-out.

It’d be easy to look at SK 54’s fate as a chilling reminder that humans spent millions of years as prey. Not merely being killed, but more specifically getting eaten, is an enduring fear. But for paleontologists, there’s a deeper lesson here: Far from being an anomaly, SK 54 represents one of many fossils that may never have made it into the fossil record without the hunger-motivated intervention of prehistoric carnivores. By helping themselves to a hot meal, meat eaters assembled a record of our past.

The textbook version of fossilization goes something like this. Alive or dead, an organism needs to be rapidly buried. Sand, mud, ash—almost any sediment will do. This geologic blanket keeps the bones safe from scavengers that would otherwise destroy and scatter the remains. Carnivores are thus cast in the role of natural enemies of paleontologists. But, in truth, fossil hunters owe a debt of gratitude to a variety of prehistoric predators—especially those who preyed on our own predecessors.

Consider the crocodile. Dozens of schlock horror movies have banked on the terror of being snaffled up by the toothy saurians, but the reptilian ambush predators of Olduvai Gorge actually did paleontologists a valuable service.

Back in the days that Homo habilis was wandering around Tanzania, around 1.8 million years ago, Olduvai was a marshland inhabited by huge, horned crocodiles. It’s difficult to say whether these prehistoric giants were able to catch the prehistoric people fresh or scavenged bodies, but a Homo habilis foot and two leg bones bear crocodile bite marks. This led paleontologist Christopher Brochu and colleagues to name the Olduvai predator Crocodylus anthropophagus – the human-eating crocodile. And while such scenes might be unsettling to envision, those crocodiles dragged human remains into an environment where sediment was being laid down and therefore fossilization could take place.

The giant hyenas of China’s Dragon Bone Hill provided a similar service. While Homo erectus – famously known of Peking Man upon discovery – are indeed found in the 750,000 – 200,000 year old sediments of the cave, the most numerous fossils belong to Pachycroctua bervirostris – a stocky hyena as heavy as a lion. This was their turf, and, according to paleoanthropologist Noel Boaz and colleagues, damage to the Homo erectus bones only reinforces the conclusion.

About 67 percent of Homo erectus bones found at the site show signs of gnawing by large carnivores, and the giant hyena in particular. There are some indications that the Homo erectus sometimes used the cave as a refuge, their tools and evidence of fire giving away their efforts to hunker down, but the overwhelming signal was that hyenas were bringing the humans back to their den to consume at their leisure.

It was a grisly process. After finishing the meat of the body, the hyenas likely ate the easily-available muscles on the outside of the skull, Boaz and coauthors proposed, before cracking off the lower jaw to get to the tongue. From there the hyenas may have braced the skulls against the cave floor to break open the cranium to get the fatty brain inside, a delicacy for the carnivores. Yet while we might wish that Pachycrocuta were gentler with our ancient relatives, their efforts nevertheless scattered Homo erectus bones in a place where they could be buried and held safely until discovery. While most of these Homo erectus bones were later lost in transit – an open mystery of Sherlockian proportions – and only survive today as casts of the originals, they were an international sensation when discovered and were among the richest human bonebeds ever found. Thanks, hyenas.

The more paleontologists and anthropologists look at the fossil record, the more it’s apparent that meat-eating animals have helped make the fossil record we now study. Owls and other birds of prey, for example, have kept a long-running record of small mammals in the pellets they deposit, and crocodylians have been unwittingly contributing to the fossil record for over 47 million years. Big cats have had a paw in shaping our view of the past, too. Leopards have been stashing their prey in caves for millions of years, and, even in recent history, cougars have made enough of a habit of stashing kills in hard-to-get places that they can sometimes confuse archaeologists. Even lions, who were thought to almost never accumulate bones, can sometimes stash impressive skeletal assemblages.

Carnivore contributions to the fossil record haven’t stopped. Today, meat-eaters in Africa like hyenas, jackals and big cats are all adding to tomorrow’s fossil record, says says Smithsonian National Museum of Natural History paleoanthropologist Briana. Of these, hyenas are our heroes. The reason why, Pobiner notes, is “mainly feeding their babies in their dens, which can be already underground.” It’s a ready-made situation for future fossilization. They may destroy a fair amount of their meals, to be sure, but better to have leftovers than no future fossils at all.

Our helpful carnivore neighbors have done more than just increase the sample size of hominin remains. They’ve also helped anthropologists put us in our place. Early visions of prehistoric people saw them as exceptionally violent and brutish. The damage on SK 54 and on the Dragon Bone Hill humans were originally interpreted to be signs of murder, and even cannibalism. But realizing that early humans were often prey helped usher in a more nuanced vision of our ancestors. These were people struggling to survive while also learning from the carnivores we feared and competed with.

Once our ancestors stopped cowering in the shadow of predators and stepped into the carnivore guild ourselves, using stone tools to stand in for slicing teeth, they inadvertently started to create a fossilized record of their favorite foodstuffs. The menu has ranged from mammoth to lemurs to seafood, scattered through caves and collected in middens. People creates records of their meals just as carnivores contributed to our own story. Which just goes to show: A hominin’s trash is a paleontologist’s treasure. 

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.