Bootherium bombifrons, an extinct musk-ox which lived 780,000–11,000 years ago, was one of at least four such species found in North America during the Pleistocene; only one still lives today. Both male and female musk-oxen have four-inch-thick horns, and the battles between males during mating season can be spectacularly violent in living musk-oxen. This specimen will be part of "Extreme Mammals: The biggest, smallest, and most amazing mammals of all time," an exhibition opening May 16, 2009, at the American Museum of Natural History
