Ancient hypercarnivores such as dire wolves, cave hyenas, and saber-toothed cats – whose diets consisted of 80% meat – were up to twice the size of the wolves, spotted hyenas, and lions we have today. And according to new findings published in Proceedings of the National Academy of Sciences, packs of them used to keep even the most humongous of Pleistocene megaherbivores in check. These hunters had a much bigger impact on the ecosystem than we thought: Killing just 17% of juvenile megaherbivores a year would be enough to halt population growth.

Work with modern-day elephants suggests that huge, hungry plant-eaters like mammoths and giant ground sloths could devastate the vegetation when densely packed. And while elephants are the largest terrestrial herbivores these days, they’re smaller, fewer, and less widely distributed than some of those prehistoric giants. So how did those ancient landscapes survive this destruction? 

“Based on observations of living megaherbivores, such as elephants, rhinos, giraffes and hippos, scientists have generally thought that these species were largely immune to predation, mainly because of their large size as adults and strong maternal protection of very young offspring,” UCLA’s Blaire Van Valkenburgh says in a statement. Yet in Botswana’s Chobe National Park, for example, 74 elephants were killed by lions over a four-year period. The majority of the kills were juveniles and sub-adults (nine years or younger), and they were typically accomplished by groups of predators working together. Sometimes one lion would jump on and bite the back of the victim, while the others sever its himblimb muscles. 

^{If they worked together, saber-toothed cats (Smilodon) may have been capable of taking down juveniles of the Pleistocene's largest herbivores. Mauricio Anton}

To study the impact of hypercarnivores in the Pleistocene, which ended about 11,700 years ago, Van Valkenburgh and colleagues developed a series of models for estimating the size ranges of both predators and their prey. For predators, they turned to fossilized first molars. “In the fossil record, the one thing we’ve got a lot of is teeth,” Van Valkenburgh adds. To infer herbivore sizes, the team developed formulas for the relationship of shoulder height to body mass using data on modern elephants. They also analyzed kills in the wild to estimate typical and maximum prey sizes hunted by single predators and those in groups. 

Juvenile megaherbivores, they conclude, would have been susceptible to predation – especially if the carnivores were organized into groups and the young herbivores were just beginning to venture out a bit to forage for themselves. A single Pleistocene cat could have killed a 2- to 4-year old mammoth, for example. And in a group, extinct lions and saber-toothed cats could have killed adult female mammoths weighing up to 6,700 kilograms (14,770 pounds). 

“We brought together a diverse array of data (fossil, historical, recent behavioral, new body mass estimates) to try to predict the typical and maximum prey sizes of the large Pleistocene carnivores,” Van Valkenburgh tells IFLScience. “And we brought up the idea that group (pride, clan, pack) sizes were probably larger in the Pleistocene – given that they were significantly larger just 60 years ago – and this would have made killing juveniles and sub-adult megaherbivores even easier for these large cats and hyenas.” Human hunting in the last century selected against large groups, since they were easier to detect.