Chapter 23

Chapter 23 - Chapter 23 Animal Diversity II Vertebrates...

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Unformatted text preview: Chapter 23: Animal Diversity II, Vertebrates Vertebrate animal evolutionary tree Primitive ancestral vertebrate Key Features of Chordates • All chordates possess four features at some stage of their lives 1. Notochord (stiff flexible rod extending the length of the body) 2. Dorsal, hollow nerve chord 3. 4. Are Humans Chordates? • Only one chordate characteristic, the nerve cord, is present in adult humans; however, human embryos exhibit all four – Tail will disappear completely – Notochord is replaced by the backbone – Gill slits (grooves) contribute to the formation of the lower jaw • As an example, observe a 5-week-old human embryo picture… eye heart liver tail limb bud (future leg) limb bud (future arm) gill slit Invertebrate Chordates • Lack a backbone • Include the lancelets and the tunicates – Lancelets are fishlike filter-feeders • Adults and larvae exhibit all key chordate features – Tunicates (sea squirts) live in a marine environment • Larvae are mobile and exhibit all key chordate features • Adults are sessile filter-feeders that have lost their tail and notochord Lancelet mouth gill slits notochord gut tail anus (b) mouth gill slits gut larva anus notochord tail water enters (mouth) water exits gill slits gut adult Tunicate Vertebrate Chordates • Have a backbone ( vertebral column ) composed of bone or cartilage (resembles bone, but is more flexible) – Supports body – Provides attachment sites for muscles – Protects nerve cord and brain Vertebrate Adaptations • Several adaptations have allowed vertebrates to successfully invade most habitats – Endoskeleton that can grow and repair itself – Paired appendages (fins, legs, wings) – Increased size and complexity of the brain and sensory structures Major Vertebrate Groups • Earliest vertebrate fossils were found in 530-million-year-old rocks – Resembled lancelets with a brain, skull, and eyes • Present-day vertebrates include jawless fishes, cartilaginous fishes, bony fishes, amphibians, reptiles, birds, and mammals Jawless Fishes • Jawless • Have eel-shaped bodies and smooth scale-less skin • Include the hagfishes and the lampreys Hagfishes • Exclusively marine (live near ocean floor) • Feed primarily on worms • Secrete massive quantities of slime as a defense against predators • Lack a true backbone (not a true vertebrate), but have a rudimentary brain case • Represent the chordate group that is most closely related to the vertebrates Hagfish Hagfish...
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Chapter 23 - Chapter 23 Animal Diversity II Vertebrates...

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