Fishes Vertebrate Evolution Oldest known vertebrate fossils Tadpole
Fishes
Vertebrate Evolution • Oldest known vertebrate fossils – Tadpole – like (6 inches 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 1 st 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 – finned) • Class Actinopterygii (ray – finned)
Class Sarcopterygii (lobed – finned) • Fins supported by main axis of bone • Lungfishes (video) – http: //www. nationalgeographic. org/media/westafrican-lungfish/ – Modified swim bladder – Breath air
Class Sarcopterygii (lobed – 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
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