Bighorn sheep have double layered skulls to protect themselves during (literally) head-to-head combat. Their horns can weigh up to 14 kg (30 pounds!). Males fight battles with their heavy heads and horns, sometimes to the death, to win access to females. Now that’s a heavy concept!
Sketch and fact contributed by Lea Pollack
Source: Bighorn Sheep – Ovis canadensis – Details. (n.d.). Retrieved from http://eol.org/pages/328658/details