Deuterostomes 2: tetrapods

most informative transitional form between tetrapods and lobe-finned fishes

Tiktaalik

tetrapod synapomorphy

four limbs

early tetrapod lineages

• amphibians

• amniotes

animals identified as amphibians

• frogs

• salamanders

• toads

• caecilians (legless amphibians)

why do amphibians need to be near bodies of water

• eggs are not dehydration resistant

• skin is not dehydration resistant

• have an aquatic larval stage which goes through metamorphosis to become adults

what two clades arise from amniotes

• reptiles (including birds)

• synapsids (give rise to mammals)

synapomorphies of amniotes critical to the colonization of land

• amniotic egg; enclosed embryo in membrane to prevent dehydration

• dehydration resistant skin made of keratin

• water-conserving kidneys

five clades of reptiles

• tuatoras

• squamata: lizards and snakes

• testudinata: turtles

• crocodilia: crocodiles and alligators

• dinosauria: dinosaurs and birds

two main lineages of dinosaurs

• saurischian dinosaurs: sauropods (long necked dinos) and theropods (most carnivores)

• ornithischian: most herbivores

where did birds arise from

feathered theropods

what did feathers initially serve for

insulation; later co-opted for flight

earliest dino capable of flight

archaeopteryx

how are dinosaurs still alive today?

as birds

synapomorphies of synapsids

• enlarged skull

• specialized teeth

• single opening in the skull behind each orbit

where do mammals arise from

synapsids

synapomorphies of mammals

• hair made of keratin

• mammary glands that secrete milk

mammalian phylogeny (3 lineages)

• monotremes: lay eggs with yolk

• therians: marsupials! embryos develop in uterus and still rely on yolk

• placental mammals: embryos develop a placenta, very little yolk

which animals are apart of monotremes

platypus

what is an effect of monotreme babies being hatched underdeveloped

long lactation period

what is the marsupium

protective pouch in marsupials

what type of placenta do female marsupials have

rudimentary, underdeveloped

what do female placental mammals possess

a true placenta connected to the mother’s blood supply

what order of placental mammals does humans belong to

primates

powerful mammalian model organism for human disease

mouse

members of the Hominidae family (great apes)

• orangutans

• gorillas

• chimps

• humans