Despite a lack of archaeological evidence, the first North Americans have often been depicted hunting with spear-throwers, which are tools that can launch deadly spear points at high speeds. But now, a new analysis of microscopic fractures on Paleo-Indian spear points provides the first empirical evidence that America's first hunters really did use these weapons to tackle mammoths and other big game. 

The new study has implications for scientists' understanding of the way Paleo-Indians lived, researchers say.

To understand the inner workings of extinct hunter-gatherer societies, it's important to first learn how the ancient peoples got the food they ate, because their lives were closely tied to their subsistence activities. Current models of Paleo-Indian society are based on the assumption that hunters sometimes used spear-throwers, or atlatls, said study author Karl Hutchings, an archaeologist at Thompson Rivers University in Canada. [In Photos: The Clovis Culture & Stone Tools]

"We can now be assured that those assumptions were right," Hutchings told Live Science.

Ancient hunting tools

Similar to bows, atlatls can propel flexible, pointed shafts — called darts, rather than arrows — at high speeds across long distances. Essentially, they were sticklike tools that contained a hook or spur at one end to hold a dart. By swinging the spear-thrower overhead and forward, hunters could launch their darts with greater force than if they were to throw them like javelins.

Archaeological evidence indicates that hunter-gathers in the Old World used atlatls beginning at least 18,000 years ago. Researchers have long thought that Paleo-Indians — including the people of the Clovis culture, who lived around 13,000 years ago and are considered one of the first American peoples — also hunted with spear-throwers.

Researchers reasoned that "if the spear-thrower originated in the Old World, then it only made sense that it must have shown up with early [North American] colonists," Hutchings said. Additionally, Paleo-Indians were thought to have hunted big animals, such as mammoths and ground sloths, which would have required powerful, long-distance weapons to take the animals down safely. "People started wondering just how crazy you would have to be to run up to these things with just a sharp, broken rock tied to a stick."

But archeological evidence of Paleo-Indian atlatls and darts is lacking because these tools were often made of wood, which doesn't preserve well — the only part of the weapons left in the archaeological record are the stone points, which could have also been used in other types of weapons, such as spears, Hutchings said. In comparison, ancient spear-throwers from Europe were often made of ivory or bone.

The earliest known evidence of Paleo-Indian spear-throwers comes from 11,000-year-old "bannerstones," which are stone objects that may have functioned as atlatl weights, though the true function of bannerstones is debated, Hutchings said. [Top 10 Mysteries of the 1st Humans]

The earliest solid evidence of atlatls in the New World, then, are 9,000- to 10,000-year-old spear-thrower hooks from Warm Mineral Springs, a sinkhole in Florida. However, these tools date back to the Early Archaic subperiod, which came after the Paleo-Indian period.

Telltale fractures

To see if the earliest North Americans — including people from the Clovis culture, Folsom culture (10,000 to 11,000 years ago) and other Paleo-Indians — used atlatls, Hutchings analyzed the fractures present in hundreds of spear points. He looked for clues that the weapon tips experienced high-velocity, mechanically propelled impacts.

If a spear point hits a target hard enough, the energy of the impact will cause the tip to break. "When it breaks, it sends a shock wave through the stone that produces fractures, which are related to the amount and kind of force involved," Hutchings said.

By measuring topographic features on the fracture surface, you can calculate the "fracture velocity" of the impact, or how quickly the fractures spread through the material, Hutchings explained. Because different weapons — spears, javelins, atlatls or bows — produce specific fracture velocities and related forces, you can work backward from a fracture to determine what caused it.

Using this method, which he developed in the late 1990s, Hutchings determined the fracture velocities for 55 out of 668 Paleo-Indian artifacts that he examined. Of these points, about half of them exhibited fracture velocities that can only be achieved using an atlatl and dart or a bow and arrow.

Because Paleo-Indians aren't thought to have had bows and arrows or other propulsive weapons, the findings suggest that they most likely used atlatls to launch their spear points, Hutchings said.

Importantly, the method may also help scientists better understand ancient projectile technologies, by allowing them to trace the origin of the technologies and how they were used across societies and continents. "We can get a better resolution of when these technologies occurred, how they spread and why they spread," Hutchings said.

Hutchings detailed his findings in the March issue of the Journal of Archaeological Science.

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