willi_b.jpg ACANTHODIANabc.jpg

They are sometimes called Spiny Sharks. In forn they resembled sharks but thier epidermis was covered with tiny rhomboid platelets. They appearead at the beginning of the silurian period, which was about 50 million years before the first sharks appeared. They had characteristics of both sharks and fish. They existed about 438 to 258 (mya). They were the earliest known jawed verterbrates.