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subphylum, do not have a true backbone, but they have the characteristics of other chordates (ex. tunicates, sea squirts)
jawless vertebrates, could not chew food, used pharyngeal slits, gills, 500 mil years ago (ex. lamprey)
major evolutionary step for fish, gills became hardened with cartilage, could eat big pieces of food
second big step for fish, cartilage became hardened due to presence of calcium salts (calcium phosphate)
first vertebrates to move on land (evolved from lungfish), increased use of limbs, dependence on oxygen
first tetrapods, mostly carnivorous, cold-blooded (ectoderms), longer snout, mobile neck, highly flexible
no operculum, large gular plates, breathes air (ex. frogs do this when their throats get big and small)
eggs laid in water, then tadpoles develop and breathe with gills, skin of adults must be moist at all times (limited habitats)
amnion membrane (protection), chorion membrane (gas exchange), allantois sac (waste disposal), yolk sac (nutrients)
evolved from amphibians, live in drier habitats, skin covered in keratin protein for protection, ectothermic but they regulate temp
large terrestrial reptiles from 300-65 mil years ago, diverse lifestyles, very agile/fast, mass extinction at end of cretaceous period
social characteristics of birds
controlled flight, complex courtship rituals, social bonding/ extended parenting, amazing navigation skills using sun/moon/stars
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