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Reptile Derivatives. Birds and mammals. Archaeopteryx = “first” bird. Reptilian features teeth, tail, pelvis – no sternum skull features Avian (bird) features feathers, longer front limbs. Shy feathers; insulation. Why fly?: to glide from tree to tree - PowerPoint PPT Presentation
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Reptile Derivatives
Birds and mammals
Archaeopteryx = “first” bird
Reptilian features
teeth, tail, pelvis – no sternum
skull features
Avian (bird) features
feathers, longer front limbs.
Shy feathers; insulation
Why fly?: to glide from tree to tree
or to chase insects?
Synapsids = mammal like reptiles
Pelycosaurs = Dimetrodon
Function of “sail”
Camoflage?
Swimming?
Thermoregulation
Note: nasty carnivore
Therapsids
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
A definition of mammal = three bones in middle ear, one bone in lower jaw
Mammals; monotremes, platypus and echidna
Lay eggs.
Echidna – egg in pouch,
Hatches in 9 days – young in pouch for 12 weeks. Gets milk.
Marsupials and Placentals –
Parallelism
And no eggs
Marsupial and placental reproduction;
clevage total and equal - blastula forms with inner cell mass
Inner cell mass forms layers of cells inside blastula
Embryo implants into uterine wall
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
Marsupial pouch with ‘baby’
opossum young on nipple.
Marsupiaols not primitive, but different
Designed for an unpredictable environment – can dump kid to save mother.