reptile derivatives birds and mammals. archaeopteryx = “first” bird
Post on 21-Dec-2015
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Reptilian features
teeth, tail, pelvis – no sternum
skull features
Avian (bird) features
feathers, longer front limbs.
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
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
opossum young on nipple.
Marsupiaols not primitive, but different
Designed for an unpredictable environment – can dump kid to save mother.
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