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CC BIO 44 - Evolution of Tetrapods Lecture Notes

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Evolution of tetrapodsSlide 2Origin of lungsSlide 4Slide 5Concept of “Preadaptation”Slide 7Earliest AmphibiaSlide 9Slide 10Slide 11Slide 12Why come out on land??Modern amphibiaSlide 15Slide 16Slide 17Earliest reptilesSlide 19Why become a reptile (why lay eggs on land)Needed to become a reptileSlide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Evolution of tetrapodsAmphibia through reptilesThe Crossopterygian fish,EusthenopteronOrigin of lungs•A gill pouch that fails to open to the outside•Carries vagus nerve into the chest•Requires a major change in circulation.Series heart to parallel heart and separation of oxygenated and unoxygenated blood.Concept of “Preadaptation”•Crossopterygian fish had lungs for breathing in low oxygen water.•Crossopterygians had muscular fins for pushing through swamp vegetation•Both features allow them to live on land.Earliest Amphibia•Very much like crossopterygians, plus•Legs•No other changes!!!•Already had lungs•Very large, heavy•Carnivores, food in water.Crossopterygians (Sarcopterygians) had fleshy fins to push through swamp vegetation.Note: 8 toesEryops – one of earliest amphibia. 6 ft long, carnivorous probably couldn’t lift chin off ground for very long. Poor limbs.Why come out on land??•Story 1.• dry period – need to find another water hole•Practice walking to it.•Story 2• young ones come into shallow water and land to avoid bigger carnivorous onesModern amphibia•Small –•Reduced head, skeleton, weight•Some better lungs (toads) some no lungs but skin respiration, some ext feather gills•Lay “fish” egg.•Big original ones eaten by reptiles? Only little inconspicuous ones remain.Surviving amphibia: frogs, toads, salamanders, legless salamanders..Axolotl. External “skin” gills unrelated to internal fish gills.Earliest reptiles•Microsaurs• a reptile because• no larva (tadpoles)• lay reptilian type egg?Larval fossil amphibian: poorly ossified limbs, in some impression of external gills.Why become a reptile(why lay eggs on land)•Free of water – metamorphosis unnecessary•No double life; plant eater in water, carnivore on land (More food available on land now (insects))•Avoid nasty predatory fish•Egg safetyNeeded to become a reptile•No metamorphosis (some salamanders)•Lay eggs on land ( some salamanders)•Internal fertilization (behavior change)•Develop egg shell (soft in some reptiles (turtles), harder in birds. Calcium deposition.•Development of extra-embryonic membranes. (the biggie)amplexusUrchin gastrulation; total and equal clevageFrog gastrulation, total but unequalGastrulation in chicken or reptile; partial clevage, primitive streakOutgrowth to form membranesDevelopment of the 4 extra embryonic membranesGrowth outwards of ectoderm and mesodermForms amnion and chorionGrowth outwards of endoderm and mesoderm forms yolk sac.Later outgrowth of endoderm and mesoderm forms the allantoisAmphibian to reptile – monophyletic due toComplexity of egg difference4 extra embryonic membranes, no intermediates.Living Reptiles: Turtles Lizards and snakes crocodilesExtinct: Plesiosaurs (aquatic) Ichthyosaurs (aquatic) dinosaurs mammal like reptilesDescendents birds (dinosaurs) mammals ( mammal like reptiles)Anapsids; solid cheek, no hole – primitive reptiles and turtles.Turtles: shell is vertebrae and ribs, limb girdles inside!Ichthyosaurs – totally aquaticplesiosaursLizards and snakesPelvic structure separates dinosaurs into two groups.Velociraptor (Jurrasic park) – had feathers.Pterosaurs = hang glider wings.Periodic mass


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CC BIO 44 - Evolution of Tetrapods Lecture Notes

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