Kingdom – Animalia
Phylum – Chordata
Subphylum – Vertebrata
Vertebrates:
Include fish, amphibians, reptiles, birds, & mammals
Have a notochord (slim, flexible rod) present in early stages that may be replaced by backbone in adults
Contain a dorsal, hollow bundle of nerves called the nerve or spinal cord
Respire through pharyngeal or gill pouches during early development
Have post-anal tail in early stages
Endoskeleton made of bone &/or cartilage
Anterior head with well developed brain & sensory organs (Cephalization)
Closed circulatory system
Taxonomy of Vertebrates:
Agnatha include hagfish & lamprey with long, eel-like bodies without jaws or paired fins & cartilage skeletons
Chondrichthyes include sharks, rays, & skates with cartilage skeletons, paired fins, & jaws
Osteichthyes are bony fish with jaws, paired fins, & bone and cartilage in their skeletons
Amphibia include frogs, toads, & salamanders that go through an aquatic larval or tadpole stage
Reptilia include snakes, turtles, lizards, & alligators that live on land, are covered with scales, & lay a tough, protective amniote egg
Aves are birds covered with feathers, adapted for flying, & with hollow bones
Mammalia have hair or fur & females have mammary or milk-producing glands
Evolution:
Fossil record shows jawless fish without paired fins appeared first about 550 million years ago
Ostracoderm was a jawless, bottom-feeding ancestor to the agnathans (modern jawless fish)
Development of jaws & paired fins allowed better movement & increased ability to capture prey
Extinct acanthodians or spiny fish were first jawed fish with paired fins
Jaws probably developed from gill arches (bone that supports the pharynx)
Characteristics of Fish:
Streamlined body & muscular tail for swimming
Most with paired fins for maneuvering
Body covered with protective scales & mucus layer to reduce friction when swimming
Have less dense body tissues & store less dense lipids to help them float
Respire through gills
Most have a lateral line system or a row of sensory structures running down each side of the organism to detect changes in water temperature, pressure, current, etc.
Most with well-developed sense of sight & smell
Some can detect electrical currents
Ectotherms (adjust body temperature to environment)
