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Evolutionary Journey: From Reptiles to Mammals

Explore the transition from reptiles to mammals, uncovering the unique features and adaptations of each group. Learn about early bird evolution, synapsids, and the defining characteristics of mammals. Delve into the reproductive strategies of monotremes, marsupials, and placentals, highlighting their evolutionary significance.

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Evolutionary Journey: From Reptiles to Mammals

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  1. Reptile Derivatives Birds and mammals

  2. Archaeopteryx = “first” bird

  3. Reptilian features teeth, tail, pelvis – no sternum skull features Avian (bird) features feathers, longer front limbs.

  4. Shy feathers; insulation

  5. Why fly?: to glide from tree to tree or to chase insects?

  6. Synapsids = mammal like reptiles

  7. Pelycosaurs = Dimetrodon

  8. Function of “sail” Camoflage? Swimming? Thermoregulation Note: nasty carnivore

  9. Therapsids

  10. How to make a Mammal • Develop for carnivory = active • Hair – warm bloodedness • Limbs; under body, toes of equal length • Teeth; regionalization, multi roots, cutting • Lower jaw – one bone • Not there – change in reproduction

  11. A definition of mammal = three bones in middle ear, one bone in lower jaw

  12. Mammals; monotremes, platypus and echidna Lay eggs.

  13. Echidna – egg in pouch, Hatches in 9 days – young in pouch for 12 weeks. Gets milk.

  14. Marsupials and Placentals – Parallelism And no eggs

  15. Marsupial and placental reproduction; clevage total and equal - blastula forms with inner cell mass

  16. Inner cell mass forms layers of cells inside blastula Embryo implants into uterine wall

  17. On plate inside embryo – primitive streak forms Get chorion, amnion, allantois and yolk sac Placenta = chorion plus yolk sac in marsupials Placenta = chorion plus allantois in placentals

  18. Marsupial pouch with ‘baby’

  19. opossum young on nipple. Marsupiaols not primitive, but different Designed for an unpredictable environment – can dump kid to save mother.

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