Giant crabs with oversized right claws are the poster crustaceans for sexual selection: the reason male crabs have such huge claws is to attract female crabs. Now, a paleontologist has discovered the fossil of an especially large giant-clawed crab of the aptly named Megaxantho family, which lived in the late Cretaceous period alongside the last of the dinosaurs.

What's interesting about this crab--besides its size--is the prominent tooth-shaped structure on its giant claw, which presumably was used to pry snails out of their shells. Also, this species of Megaxantho lived 20 million years earlier than paleontologists had previously believed, which may cause some rapid rewriting of the "crustaceans" section of biology textbooks.