You wouldn’t want to find yourself on the business end of a New Guinean bone dagger. In previous centuries, warriors on the South Pacific island used these blades in close-quarters combat to kill outright, finish off foes wounded by arrows or spears, or disable and capture enemies.
The elaborately decorated daggers were primarily made from the leg bones of large flightless native birds called cassowaries (like the bottom dagger pictured above), potent symbols of agility and aggression. More rarely, they were fashioned from human thigh bones taken from battle-proven warriors (the top two daggers pictured). Yet, historical cassowary daggers tend be relatively flat, whereas human bone daggers are relatively more curved, and nobody is quite sure why.
To find out, a team of anthropologists and engineers investigated the structural mechanics of blades made from the different bones. A computerized tomography scanner analyzed density and geometry, while a tension machine and computer simulations assessed how much force was required to break the weapons.
The human thigh daggers’ curvature granted the blades more mechanical strength, able to withstand about 31% more force than the cassowary daggers before breaking, the researchers report in Royal Society Open Science. That suggests warriors engineered their human bone daggers to be strong and durable, perhaps to preserve their symbolic value. On the battlefield, however, they may have preferred the relatively weaker, flattened cassowary daggers, which may have been lighter to carry or easier to stab into enemies.