I have to apologize to carnivores. In an article about how to become a fossil, published last summer, I wrote that I wasn’t enamored with the idea of being deposited in the fossil record as bone scraps in carnivore dung. That’s still true, but I should have done more than make a passing joke about my fossilization preferences. There’s more to the story than scat. Carnivores have contributed greatly to literally assembling the fossil record.
From crocs to hyenas, predatory animals past have inadvertently assisted paleontologists by bringing their meals to lake bottoms, caves, and other places amenable to preservation. Worse for wear the skeletons they may be, but it’s better to have bitten bones than none at all. And among all these carnivorous accumulators, leopards have been especially helpful.
Watch any nature documentary about big cats and you’re likely to see a guarding a kill the cat has stashed up a tree. Prehistoric leopards likely did the same, but they also dragged carcasses back to caves. Lairs replete with bones are cat-created records of prehistoric fauna, including early humans, and one such Ice Age site in northeastern Spain is the focus of a new PLoS One paper by paleontologist Víctor Sauqué and colleagues.
Known as Los Rincones, the cave contains a Pleistocene mix of mammals that lived in the area prior to 12,000 years ago. From 1,443 collected fossils, the researchers counted brown bear, wolf, leopard, lynx, red deer, roe deer, Spanish ibex, Pyrenean chamois, a large bovid, and two horse species among the large mammals. From the details of those bones – including the ages of the animals that deposited them to the pattern of remains preserved – Sauqué and coauthors concluded that leopards were the primary agents creating the assemblage. To do that, though, they had to navigate some tricky aspects of the boneyard.
Looking at the representation of animal remains found in Los Rincones, brown bears might initially seem to be the most important carnivores. Their skeletons are far more complete and significantly more numerous than those of leopards, embodying a range of ages from cubs to adults. But rather than representing a predatory presence, Sauqué and colleagues argue, these aspects of the bear bones indicate that the ursids were hibernating in the cave. Maybe they chewed on bones already there, but, since bears aren’t known to take food back to lairs, their numerous bones mean that they used Los Rincones as a spot to snooze more than anything else.
A few of the cave’s bones also bear cutmarks made by humans. Was the cave a slaughterhouse used by prehistoric people? Unlikely. The cut marks and remnants of stone tools are few, and there’s no sign of sustained human presence. People may have used the cave to butcher kills on occasion, Sauqué and coauthors suggest, or the bones could have been scavenged by carnivores after humans had taken their share from carcasses. If humans stopped by the cave at all, they didn’t stay.
Given that the cave’s bones looked to be accumulated by animals, rather than washed in from the outside, this left Sauqué and colleagues with two candidates – hyenas and leopards.
Hyenas are bone hoarders, and also roamed across Spain during the last Ice Age. But they probably had little, if anything, to do with Los Rincones. For one thing, no sign of hyenas has been found in the cave so far. No scat, no bones chawed in a hyena-like fashion, no milk teeth from the pups they would have raised there. Not to mention that hyenas often tear off pieces of larger mammals to run back to their dens. A hyena-created cave assemblage would have elements from mammoths and other big beasts, which are lacking at Los Rincones.
Leopards are a better bet. Not only are they the second most common carnivore at the site – their bones making up a little more than 12% of the recognized fossils – but the details of the rest of the assemblage fit their modus operandi. The majority of the herbivorous animals found in the cave are juveniles of mid-sized herbivores such as the especially-prevalent Spanish ibex. These horned herbivores fit within the preferred prey range seen among leopards alive today – big enough for a good meal, but not so big as to be impossible to haul away to a secretive spot. More than that, leopards left the skeletons of the carcasses much more intact than hyenas would. Cats mainly feed on soft tissues with hyenas are capable of crunching bones down to shards.
Based on the fossil trail the cats left behind, it seems that the leopards pounced on unwary ungulates that grazed and browsed near the cave. Rather than dismember their prizes at the scene, though, the spotted felids dragged their kills back to the cave to eat in relative safety, littering the lair with skeletal leftovers. The cats didn’t stay there permanently – brown bears and humans left their mark on the assemblage as they took their turns in Los Rincones – but leopards were responsible for hoarding most of the fossil riches paleontologists now pick over. Thanks, cats.
Sauqué, V., Rabal-Garcés, R., Sola-Almagro, C., Cuenca-Bescós, G. 2014. Bone accumulation by leopards in the Late Pleistocene in the Moncayo Massif (Zaragoza, NE Spain). PLoS ONE. 9, 3: e92144. doi:10.1371/journal.pone.0092144