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Chordates, Part 2

Chordates, Part 2. Subphylum Vertebrata (cont.). Plus paired appendages (2 pair). Cranium formed from neural crest cells. Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands). The amniotic egg. Shell : Retains water

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Chordates, Part 2

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  1. Chordates, Part 2 Subphylum Vertebrata (cont.)

  2. Plus paired appendages (2 pair) Cranium formed from neural crest cells Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands)

  3. The amniotic egg • Shell: • Retains water • Allows for terrestrial existence • Gases (oxygen and carbon dioxide) diffuse freely • Calcareous & inflexible (birds) OR • Leathery & flexible (reptiles) • The albumin (just inside the shell) is one source of nutrients

  4. Amniotic egg: Extraembryonic membranes • Chorion: • Mediates gas exchange with the external environment • Gases flow freely through albumin (egg white) • Amnion: • Membrane forms fluid-filled sac that houses embryo • Fluid absorbs shock • Allantois: • Disposal sac for metabolic waste • Yolk Sac: • Membrane surrounding nutrient stockpile

  5. Chapter 34: Vertebrate Evolution & Diversity What are the Classes of Amniotes?

  6. Class Reptilia: Diversity • Testudines(Turtles) • Evolutionary relationships uncertain • Sphenodontia(Tuataras) • Only found on New Zealand • Believed to be oldest order • Crocodilia(crocs, alligators) • Largest reptiles • Closely related to dinosaurs • Squamata(Snakes and lizards) • Most numerous and diverse group

  7. Class Reptilia • Adaptations for terrestrial living • Amniotic egg • Keratinized scales provide waterproofing • Vascularized lungs • Circulatory system • Some division into pulmonary and systemic circulation • Allows oxygenation of blood before circulation to body • Well-developed kidney that aids in water retention • Internal fertilization • Shell covering added after fertilization

  8. Closest living relatives: Crocodilians Thought to be closely related to an extinct group of dinosaurs similar to velociraptor Archaeopteryx, a fossil “reptile-bird” from 150 million years ago, shows clear reptilian characteristics Evolutionary branchpoint: Class Aves

  9. Class Aves: Diversity • 28 orders • 60% are within Order Passeriformes • Perching birds (a.k.a. songbirds)

  10. Class Aves: special adaptations • Adaptations for flight • Feathered wings (airfoils) • Honeycombed bones with hollow spaces • Light for flight! • Reduction of organs • Females have one ovary • Absence of teeth • Light for flight! • Endothermic • Higher metabolic rates needed for flight • Acute visual systems • Coordination of flight • Respiration: efficient, one-way flow • Circulation: four-chambered heart • Other behavior adaptations • Elaborate courtship • Substantial parental care

  11. Plus paired appendages (2 pair) Cranium formed from neural crest cells Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands)

  12. Class Mammalia: Key characteristics • Mammary glands (milk production) • Hair • Endothermic • Efficient circulatory system (4-chambered heart) • Efficient respiratory system (diaphragm) • Internal fertilization • Relatively large brains compared to similarly-sized vertebrates • Differentiation of teeth • Development of 2 additional earbones (see next slide)

  13. Evolution of earbones

  14. Major mammalian groups

  15. Monotremes (platypus/spiny anteater) • Egg-laying mammals • Hair • produce milk (no nipples) • Marsupials (kangaroos and koalas) • Born early in development • Completes development while nursing (usually in pouch) • Confined primarily to Australia • Eutheria (placental mammals) • Complete embryonic development within uterus • Extensive placenta • exchange of nutrients and gas between mother and offspring

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