Week 3 - Origin of Birds and Mammals

Endotherm

controls internal body temperature through internal means (metabolism, fat burning, muscle shivering)

Homeotherm

maintains a stable internal temperature regardless of external factors

Avian major evolutionary events

feathers, homeothermy, flight

Avian characteristics

feathers, four-chambered heart, oviparity, one ear ossicle, endothermic homeotherm, flow through respiratory system, bill (no teeth), hollow and fusion of bones, excrete uric acid

Evolution of powered flight body form alterations

weight reduction, size reduction, flapping mechanics

dromaeosaurs

flexible and rotating wrist structure, shift in shoulder joint

Archopteryx

transitional fossil between reptiles and birds, first true bird, revealed link between dinosaurs and birds

arboreal hypothesis

jumping to gliding to flapping, leap between trees

cursorial hypothesis

running to gliding to flapping, flapping gives forward propulsion

Mammalian characteristics

hair (derived from scales), endothermic homeotherms, lower jaw made up of a single bone on either side, 3 ear ossicles, diphodonty, heterodont dentition, 4-chambered heart, mammary glands, viviparity (most)

Pelycosaurs

'sail backs' / dimetrodon, extinct, early synapsids

Therapsids

derived synapsids

Cynodonts

advanced therapsids: cynognathus ("dog jaw") displayed more mammalian characteristics

Major mammalian anatomical changes

jaw articulation (articular-quadrate to squamosal-dentary), middle ear (jaw bones moved to ear), locomotion (sprawling to under body)

Diarthrognathus

transitional fossil with both jaw articulations (reptilian and mammalian)

Prototheria

monotremes; egg laying (reptilian structure), hair, mammary glands, warm blooded, three middle ear bones

Metatheria

marsupials; born very early in development, short gestation period, hang out in marsupium while they complete development

Eutheria

placental mammals; complete embryonic development within uterus, joined to mother by true placenta, includes species adapted for a wide range of habitats and regions