The first people to inhabit the Americas had a singular obsession: the biggest animals on the landscape. A July 2026 study in Science Advances makes the case that Paleolithic populations from Alaska to Patagonia built their entire way of life around killing multi-ton herbivores, and that this strategy explains both the animals’ astonishingly rapid continental spread and the wave of extinctions that followed.

An international research team—led by Ben Potter from the University of Alaska Fairbanks and James Chatters from McMaster University—compiled evidence from 50 archaeological sites scattered across the Western Hemisphere. At each location, they cataloged animal remains and estimated how much meat different species would have provided.

The team’s goal was to figure out whether early Americans ate broadly, taking a bit of everything each new region offered, or simply zeroed in on a few giant prey animals. “One of two competing ideas is dietary generalization: exploiting a wide variety of resources that would differ based on region,” Potter said in a statement. “The other is megafaunal specialization: focusing on just a few large-bodied prey.”

The data overwhelmingly favors specialization. The researchers focused on three of the earliest and most widespread cultural groups known to have lived in the Americas: the Eastern Beringians of Alaska and the Yukon, the Clovis people of North America, and the Fishtail Projectile Point people of South America. Researchers found that in all three groups, between 83 and 88 percent of the edible biomass at archaeological sites came from megaherbivores—the very largest plant-eating animals, each weighing more than a ton.

The term “megafauna” refers broadly to animals heavier than about 100 pounds—a category that, in Ice Age America, included everything from deer-sized camelids up to mammoths. Megaherbivores are the giants at the top of that scale: multi-ton vegetarians like woolly mammoths, elephant-like gomphotheres, and bus-sized ground sloths.

The findings suggest that the first Americans were not generalist foragers sampling whatever the landscape offered, but dedicated big-game hunters who overwhelmingly targeted the continent’s most colossal herbivores. To strengthen their conclusion, the scientists calculated how many animals of each size class would naturally have inhabited the surrounding landscape, and compared those expected ratios to what actually turned up in camp refuse. They even ran sensitivity tests that deliberately overcounted smaller animals, but the giant herbivores still dominated. “Animals like mammoths and ground sloths, which were actually quite rare in the landscape, completely dominate the archaeological record,” Potter said. “Rabbits and mice, which would have been everywhere, barely register.”

That shared dietary focus also left a clear fingerprint in the toolkits that these groups carried. Weapon assemblages from sites thousands of miles apart look strikingly alike. All of them include heavy fluted spear points and butchering blades designed for thick hides and massive joints, but gear for catching fish or processing seeds is conspicuously missing.

The megaherbivore strategy also solved a logistical problem that would normally slow down any migrating population. Learning to exploit an unfamiliar ecosystem—which small animals to trap, which plants are safe to eat, and so on—typically takes generations. Hunters who simply followed mammoth herds could skip that learning curve entirely. “Mammoths, for example, can cover a tremendous range and occupy vast territories,” said co-author Mat Wooller, also of UAF. “In effect, specialist hunter-gatherers used their knowledge of megaherbivores, like mammoths, to expand successfully across the continents rather than learning about each localized ecosystem they encountered.”

The consequence of that efficiency was grim for the prey. The study documents a southward-rolling wave of extinctions that mirrors the chronology of human arrival. Large mammals vanished from Alaska roughly 13,300 years ago, from the mid-continent around 12,800 years ago, and from South America by approximately 11,600 years ago. Each disappearance came shortly after people first reached the region.

The giant herbivores were uniquely vulnerable. They reproduced slowly, bore calves at wide intervals, and because they evolved without human predators, they possessed no instinctive fear of approaching hunters. “They would have had no learned wariness of new, technologically sophisticated human hunter-gatherer populations,” Potter noted.

Once local megaherbivore populations collapsed, the people who depended on them had little choice but to push onward into territory where giant prey still roamed. This perpetuated the cycle of human arrival and megafauna extinction until the largest species in the Americas were entirely gone.