Fish - structures to perform new functions. Jaws are...

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Fish: Vertebrates With Jaws The fish first appeared during the Cambrian Period. Whether fish first evolved in fresh or salt water is unclear from the fossil record. The jawless fish are the most primitive group, although they were a very important group during the Silurian and Devonian periods. Hagfish and lampreys are the only living members of this class today. They have long, cylindrical bodies with cartilage skeletons and no paired fins. The first jawed fish were the Placoderms, an extinct group of Devonian-aged jawed fishes. Placoderms were armored with heavy plates and had strong jaws and paired pectoral and pelvic fins. Paired fins allow fish to balance and to maneuver well in water, which facilitate both predation and escape. The evolution of jaws is an example of evolutionary modification of existing
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Unformatted text preview: structures to perform new functions. Jaws are modified gill arches, and allowed the exploitation of new roles in the habitats: predators with powerful jaws. There are two classes of jawed fish: the cartilaginous fish and the bony fish. Class Osteichthyes, the Bony Fish There are about 20,000 species of bony fish, found both in marine and freshwater, comprising the class Osteichthyes.This class is divided into two groups: the lobe-finned (Sarcopterygii) and ray-finned fish (Actinopterygii). The bony fish have a bony skeleton. Most species in this class are ray-finned with thin, bony rays supporting the fins. A few fishes are lobe-finned and are thought to be related to the ancestors of amphibians....
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Fish - structures to perform new functions. Jaws are...

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