Lecture 17 - chordates II - IV. The reptiles A. Extant...

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Lecture 18 – Chordates II I. The evolution of legs A. Tiktaalik 1. Has many fish-like traits (e.g. fins, scales, primitive jaws) 2. Has tetrapod-like traits (e.g. fins with wrist, neck, expanded ribs) B. Duplication of hox genes coding for tail create set new sets of appendages (i.e. legs) C. Digit number highly variable in early tetrapodomoph legs II. Evolution of Amphibians A. Important traits 1. Breath through lungs, gills and skin 2. Fertilization external 3. Reproduction tied to water III. Evolution of the Amniotes A. Amniotic egg 1. Amnion - protects and provides shock absorbtion 2. Yolk sac- stockpile of nutrients for embryo 3. Allantois - disposal sac for metabolic waste 4. Chorion - allows for respiration across shell B. Reproduction independent of water C. B. Internal fertilization D. Legs rearranged for carrying weight out of water
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Unformatted text preview: IV. The reptiles A. Extant reptiles (Turtles, crocodilians, birds, tuatara and squamates) B. Extinct reptiles (pterosaurs, dinosaurs, plesiosaurs and ichthyosaurs) V. The mammals - produce milk, have hair A. Monotremes 1. Lay eggs, produce milk (but no nipples) 2. E.g. platypus and echidna B. Marsupials Lecture 18 Chordates II 1. Rudimentary placenta, nipples 2. Pouch for fetal development 3. e.g. kangaroos, opossum C. Eutherians 1. Complex placenta 2. e.g. rodents, whales, bats, primates, elephants) 3. Primates a. Derived traits 1. Opposable thumb 2. fingerprints 3. large brain b. Two groups 1. Prosimians (e.g. lemurs and tarsiers) 2. Anthropoids (monkeys and apes) a. Hominids (apes) 1. Homo a. Bipedal b. Enlarged cranial cavity / brain c. Reduced lower jaw d. Many species of homo coexist...
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Lecture 17 - chordates II - IV. The reptiles A. Extant...

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