ST. PAUL, MINNESOTA--Until 10,000 years ago, a menagerie of big animals roamed North America, including fearsome predators like saber-toothed cats. Not all of the killing was done by carnivores, though. Rival mastodons, stoked by surging hormones, occasionally battled to the death, according to research presented here 18 October at the annual meeting of the Society of Vertebrate Paleontology. "It's a nice piece of paleo-forensics," says Blair Van Valkenburgh of the University of California, Los Angeles.
Mastodons and mammoths are extinct relatives of modern elephants. At 8 to 10 tons, mastodons are some 30% more massive than elephants, and their tusks are more curved. While studying six mastodons from the Great Lakes region, paleontologist Dan Fisher of the University of Michigan, Ann Arbor, came across signs of injuries that suggested a behavior found in elephants. When male elephants are in heat, called musth, they often establish dominance by knocking heads or tangling with their tusks.
In several mastodons, Fisher spotted what he interprets as signs of combat. This includes broken ribs and tail vertebrae--places where elephants in musth get injured. Looking closely at the tusks, Fisher found evidence of strong ligaments that would have absorbed shocks, which is consistent with dueling tusks. "You wouldn't expect that for other tusk uses." Moreover, the tips of tusks were fractured so badly that they probably would have been broken if ever used again; this suggests that the animals died shortly after hitting something. That something may have been other males, because several skulls had puncture wounds that could have been inflicted by a tusk. "The adult males sometimes did fight to the death," Fisher says.
Was it for love? The growth rings in the tusks show that the animals died in the late summer, not a normal time for mastodon mortality, Fisher says. The rings also suggest that the animals had been fasting before death. Elephants in musth, Fisher notes, are so fixated on sex that they neglect to eat.
"This was definitely conflict between two mastodons," says paleontologist Jeffrey Saunders of the Illinois State Museum in Springfield. He finds the extreme violence somewhat surprising because his own work on mastodons in Missouri came up with few signs of traumatic injuries. "I don't think that we've captured the whole fabric of aggression in these animals," Saunders says.