The belemnite is an extinct order of cephalopods which appeared in the late Jurassic period (213–144 million years ago) and lived through the Cretaceous period (144–65 million years ago), with a few persisting into the early part of the Tertiary period (65–2 million years ago) up to 45 million years ago. Entirely marine creatures, belemnites were characterized by a bullet-shaped, cylindrical shell.