Evolution of tetrapods. Amphibia through reptiles. The Crossopterygian fish, Eusthenopteron. Origin of lungs. A gill pouch that fails to open to the outside Carries vagus nerve into the chest Requires a major change in circulation.
Amphibia through reptiles
Series heart to parallel heart and separation of oxygenated and unoxygenated blood.
probably couldn’t lift chin off ground for very long. Poor limbs.
Larval fossil amphibian: poorly ossified limbs, in some impression of external gills.
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)
Frog gastrulation, total but unequal
Gastrulation in chicken or reptile; partial clevage, primitive streak
Growth outwards of ectoderm and mesoderm
Forms amnion and chorion
Growth outwards of endoderm and mesoderm forms yolk sac.
Later outgrowth of endoderm and mesoderm forms the allantois
Complexity of egg difference
4 extra embryonic membranes, no intermediates.
Lizards and snakes
mammal like reptiles
mammals ( mammal like reptiles)