Edestus
(Edestus heinrichi)

Living during the Carboniferous period, Edestus was another of the ocean's ancient shark-like oddities. Rather than shedding old teeth like modern sharks, it simply grew new ones continuously from the back of its jaw, pushing the old teeth forward until they protruded beyond the front of its mouth in two curved, blade-like rows — one above and one below. The result was a set of jaws that looked like a pair of giant, gaping scissors, earning it the nickname "scissors-tooth shark!"