Fishes

Vertebrate Evolution Oldest known vertebrate fossils Tadpole – like (6inches in length) Jawless fish were only vertebrates for more than 50 m.y.a

Vertebrates (Subphylum Vertebrata) Backbone enclosing a nerve cord, or spinal cord Phylum Chordata Notochord Pharyngeal pouches Postanal tail Dorsal Nerve Chord

Phylum Chordata Subphylum Vertebrata Super Class Agnatha Jawless fishes Class Myxini (Hagfishes) Class Cephalaspidomorphi (Lampreys) Class Chondrichthyes, Cartilaginous fishes, (Sharks, Sharks and Rays, Ratfishes) Class Osteichthyes, Bony fishes Class Actinopterygii (Ray – finned) Class Sarcophterygii (Lobe – finned)

Fig. 8.1

Tab. 8.1

Class Agnatha: Jawless Fishes Hagfishes and lampreys lack jaws, most primitive of living fishes Feed by suction Lack paired fins and scales Hagfish (slime eels) No vertebrae Retains notochord Lampreys, freshwater Primitive Vertebral column composed of cartilage

Origin of Jaws and Paired Fins 450 m.y.a Paired fins increased fishes’ stability and maneuverability Jaw allow to seize prey Jaws are thought to have evolved from 1st pair of gill arches (support pharynx)

Class Chondrichthyes: Cartilaginous Fishes Sharks, rays, skates, and ratfishes Endoskeleton of cartilage Paired fins, movable jaws, gill slits Rough sandpaper – like skin placoid scales pointed tip that is directed backward same composition as teeth

Fig. 8.4

Super Class Osteichthyes: Bony Fish Largest group of living vertebrates Gills covered by operculum Usually swim bladder Highly maneuverable fins Cycloid scales

Superclass Osteichthyes: Bony Fish Class Sarcopterygii (lobed – fin finned) Class Actinopterygii (ray – finned)

Class Sarcopterygii (lobed – fin finned) Fins supported by main axis of bone Lungfishes (video) http://www.nationalgeographic.org/media/west-african-lungfish/ Modified swim bladder Breath air

Class Sarcopterygii (lobed – fin finned) Coelacanth Were thought to be extinct but were rediscovered in West African waters Coelacanth species are thought to be ancestors of amphibians

Class Actinopterygii (ray – finned) Most common of boney fish