Evolution of Sharks

2093 WordsDec 24, 20109 Pages
Insert Name: Instructor’s Name: Course: Date: 08/July/2010 Sharks have been in existence for more than 300 million years. Their evolution occurred over 150 million years earlier than that of the dinosaurs. Most of the existing fossil data of early sharks was collected from fossilized teeth together with several skin impressions. primitive sharks (Cladodonts) , had teeth which were double-pointed, up to 2metres in length, ate fish as well as crustaceans, and existed approximately 360 million years ago. The earliest shark-like beings shown in the fossil records seem to have existed towards the start of the Silurian age, close to 450 million years ago, however the earliest fossil teeth known of actual sharks was…show more content…
One species incorporated the xenacanth sharks. They seem to have avoided extermination by relocating into freshwater. One group, Xenacanthus, was a seventy five centimeters in length, eel-like shark that looked like a modern conger eel. Its dorsal fin extended along its back and around the tail and connected to an odd double anal fin. The main striking feature was a single self-protective spine growing from the top of its head. Other survivors were the hybodonts, they were unspecialized sharks that looked like modern sharks but weren’t immediate ancestors. Their triumph confirmed that the fundamental shark structure and manner of life had evolved effectively millions of years before present sharks appeared. At the beginning of the Jurassic era, two hundred and thirteen million years ago, the initial 'modern' sharks were testing the hybodonts. The new sharks had extra flexible jaws that were capable of thrusting frontwards, providing them with a distinct advantage in the struggle for food. The hybodont ancestry started to end, and sharks amazingly similar to current species began to take over. Hybodonts Throughout the early Paleozoic and Mesozoic ages, the major sharks belonged to a set called Hybodontoidea. They had fins and bony structure
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