Prehistoric Sharks By Kelsey Hayes
How do we define sharks • sharks are a suborder of fish whose skeletons are made out of cartilage rather than bone • distinguished by their streamlined, hydrodynamic shapes, sharp teeth, and sandpaper-like skin. • skeletons made of cartilage so many prehistoric sharks are known primarily by their fossilized teeth.
Cladoselache • Meaning “branch toothed shark”. • Most prehistoric shark • Lived in oceans worldwide • Most famous for, not having scales like the sharks we know today • The teeth were not sharp, but blunt and smooth.
Cretoxyrhina and Squalicorax • They are recognizable as "true" sharks by a modern observer because of their size.
How old are sharks what fossils do we find • First sharks are believed to have evolved during the Ordovician period, about 420 million years ago. Tetrapods first appeared on earth 400 million years ago. • Fossil teeth are the most commonly found among sharks, however some skeletons have been found; especially of the genus Hybodus.
Sources • http://dinosaurs.about.com/od/otherprehistoriclife/a/prehistoric-sharks.htm