Prior to the conclusion of the Pleistocene Epoch, Earth boasted a vibrant population of enormous animals, including armadillo ancestors the size of a Volkswagen Beetle, ground sloths weighing up to 9,000 pounds and beavers the size of a black bear.

Today, the planet’s largest creatures—known collectively as megafauna—are decidedly smaller than these prehistoric counterparts. But as Marlene Cimons writes for Nexus Media, contemporary giants such as African elephants, rhinoceros and giraffes face many of the same threats as their extinct predecessors. First and foremost, according to new research published in Conversation Letters, is human activity, or more specifically, the killing of megafauna for their meat.

To assess the state of the world’s megafauna, a team of international researchers led by scientists from Oregon State University surveyed the populations of 292 large animal species. Of these, 70 percent, or just over 200, were classified as decreasing in number, while 59 percent, or 171, were deemed at risk of extinction.

Crucially, the team reports in the study, “direct harvesting of megafauna for human consumption” represented the largest individual threat for all six classes of vertebrates analyzed. Harvesting megafauna for meat presents a direct threat to 98 percent of the at-risk species included in the research. Additional threats include intensive agriculture, toxins, accidental entrapment, capture for medicinal use and invasive competitors.

Live Science’s Brandon Specktor explains that the researchers set various weight thresholds to determine whether an animal could be considered megafauna. Mammals, ray-finned and cartilaginous fish had to weigh in at more than 220 pounds, while amphibians, birds and reptiles needed to tip the scales at more than 88 pounds.

The final group of established megafauna, according to Newsweek’s Kashmira Gander, included such little-known creatures as the Chinese giant salamander, an alligator-sized amphibian prized as a delicacy in certain parts of Asia, and the Somali ostrich, a flightless bird hunted for its meat, feathers, leather and eggs. Better-known animals featured in the study include whales, sharks, sea turtles, lions, tigers and bears.

The scientists’ findings suggest that megafauna are far more vulnerable to extinction than vertebrates as a whole. (As Specktor points out, only 21 percent of all vertebrates are threatened with extinction, while 46 percent have declining populations.) This trend has become increasingly apparent over the past 250 years. During this time period, according to Oliver Milman at the Guardian, nine megafauna species, including two varieties of giant tortoise and two types of deer, have gone extinct. The decline is in part due to what Specktor describes as “human over-hunting and habitat encroachment.”

Quartz’s Chase Purdy explains that humans’ ascension to the role of “Earth’s super-predator” began toward the end of the Pleistocene, when our species became increasingly technologically savvy and started using projectile weapons to hunt larger animals from a safe distance. Today, however, humans no longer need to rely on megafauna for food. As Purdy notes, the majority of contemporary food sources derive from agriculture and aquaculture, while most “wild” meat stems from the capture of smaller, and often more abundant, prey.

"It’s a complex issue,” lead author William Ripple, an ecologist at Oregon State University, tells the Guardian’s Milman. “Sometimes large animals are killed for trophies, sometimes it’s subsistence hunting and fishing, sometimes it’s illegal poaching—it runs the gamut."

Ripple continues, “Humans have become super predators who don’t even have to come into contact with the things we are killing. Many of these large animals have low reproduction rates so once you add in that pressure they become vulnerable.”

Effective megafauna conservation will require the minimization of direct harvesting for meat or other body parts, the authors write in the study. Although such curbing efforts will likely have little influence on food supply, the team admits that “economic values, cultural practices and social norms might complicate the picture.”

Still, Ripple says in a press release, “If we don’t consider, critique and adjust our behaviors, our heightened abilities as hunters may lead us to consume much of the last of the Earth’s megafauna.”