Phylum Chordata - Chordates Internal skeleton with muscle ...

Sharks became dominant predators about 300 myaClass Chondrichthyes - sharks, skates, raysSkeleton is made of cartilageHave bony teeth and scales with enamelHave always been large agile predatorsenlarged pectoral fins allow greater lift andmaneuvering during swimmingHave internal fertilizationyoung are well-developed when bornskates and rays have flattened bodies andare more sedentaryClass Osteichthyes - bony fishesEvolved at same time as sharks, but in freshwaterDeveloped heavy skeleton made completely of boneOssification replaces cartilage with boneExternal plates and scales also made of boneAdded swim bladder for respiration/buoyancyPrimitive fishes use swimbladder for respiration - a lungModern fishes use swimbladder for buoyancy