Birds, Mammals, Circulation


Almost 200 million years ago, the first birds appeared

Birds are tiny dinosaurs

There are a lot of clues that birds are reptiles

  • scales

  • same amniotic egg (birds are oviparous)

Unlike reptiles, after the egg hatches, birds often do bi-parental care

  • mom and dad are bringing food to the nest to help out

  • over 90% of bird species are monogamous

  • many birds form pair bonds

Another thing that sets them apart is adaptations for flight

  • they have feathers

  • feathers came from reptile scales (both are homologous)

  • air is not only pushing from below, but pulling from above

  • lift is aided by wing shape

    • air that is passing the wing on the top side has farther to travel than the air that is passing beneath (decreasing air pressure above, greater air pressure below)

  • feathers are made of strands interlocked with hooklets

  • feathers good for insulation

Birds are light

  • lost their teeth

  • bones are mostly hollow

  • reduced some of their internal organs (no urinary bladder, only 1 ovary)

  • however sternum is not light

    • it has a keel (flat plate that sticks out)

    • acts as an attachment point for flight muscles


Birds are very mobile, so they rely on their long range senses

  • good vision

    • vast majority of birds are diurnal (active during the day time)


Archaeopteryx

  • complete transitional fossil

  • early birds with feathers

  • fossil shows imprints of teeth and tail bone (modern birds don’t have this anymore, but reptiles do)

Mammals first appeared 200 million years ago (age of dinosaurs)

  • some of the early mammals co existed with early dinosaurs

  • while the dinosaurs reigned, the mammals were a small group

    • the ones that did exist were tiny creatures like mice

  • mammals didn’t get to diversify until around 65 million years ago after the dinosaurs went extinct


Mammal traits

  • endothermic (like the avian reptiles, they control body temperature by generating heat)

    • mammals have hair to keep the heat insulated

    • hair is made of keratin (same protein found in reptile scales and bird feathers)

  • many are nocturnal

  • good olfaction (good sense of smell)

  • good sense of smell (except for primates)

  • 3 middle ear ossicles (tiny bones that are hooked to the inside of the ear drum)

    • they’re there to amplify sound

    • other tetrapods only have 1

  • 4 chambered hearts inherited (better for oxygen delivery)

  • to inhale, contract diaphragm muscle and it lowers, decreasing air pressure in the thoracic cavity

    • diaphragm relaxed: curves up, pressure up, air out

  • teeth are heterodont (different tooth shapes)

    • flat incisors

    • canine teeth

    • pre molars and molars

    • reptiles, amphibians and fish are homodont

  • good maternal care


3 types of reproduction

  1. monotremes (egg laying mammals) = oviparous

    • amniotic eggs

    • ex: platypus, spiny anteater

  2. marsupials = short gestation in uterus, newborn climbs to pouch to finish development

    • ex: opossum, koala, kangaroo

  3. placental = placenta in uterus filled with blood to exchange nutrients from moms blood to fetal blood

    • connected by umbilical cord


Orders of placental mammals

  • rodentia (biggest) = mice, rats, beavers, capybara, squirrels, porcupines, hamsters, gerbils

  • chiroptera = bats

  • primate = monkeys, prosimians (lemurs, etc), apes

  • carnivora = wolves, coyotes, foxes, lions, tigers, bobcats (cats and dogs), bears, raccoons, weasels (otters, minks, ferrets), mongoose, seals, sea lions, walrus

  • cetartiodactyl = whales, dolphins, even toed hoofed mammals (cows, sheep, camel, deer, hippos, girraffes)

  • lagomorpha = rabbits, hares, pika

  • perissodactyl = hoofed mammals with odd number of toes (horses, zebras, rhino, tapir)

  • proboscidea = elephants (long trunks)

  • eulipotyphla = hedgehogs, moles, shrews

  • xenarthra = anteaters, armadillo, sloths (weirdly arched backs)


learn 5 orders for exam, 3 examples each


Mammalian circulation

  • bottom ventricles are strong

2 atrioventricular valves + 2 semilunar valves

4 valves = one way doors

Aorta = big powerful artery, first artery of systemic circuit, a lot of blood coming past here

Vena cava = leads to right atrium

Pulmonary arteries = on the way to lungs

Pulmonary veins = carry oxygenated blood from lungs to left atrium


When listening with a stethoscope, first half of bump is the closing of atrioventricular, second half is closing of semilunar

If they don’t close right = heart murmur

Each time the ventricles contract and relax, that is 1 heart cycle


Heart cycle = systole (ventricles contracting, blood is leaving the heart) and diastole (ventricles relaxing, blood is entering)


  • as blood leaves the ventricle, it enters the vessels (more than 50,000 miles of blood vessels)

5 types of blood vessels

  1. enters arteries first (carry the blood away from the heart), each one branches into…

  2. arterioles are small arteries that branches into lots of…

  3. capillaries (smallest vessels) go everywhere, walls are porous (where atoms and even cells can enter and leave the blood), they converge into…

    • pores allow blood to give food monomers to cells

    • as cells produce waste, they travel to the excretory system

  4. venules (small veins) converge into larger…

  5. true veins (carry the blood back to the heart)


Region in the wall of the right atrium called…

sinoatrial node = controls rhythm of contraction (can contract like a muscle and send electricity like a nerve) aka pace maker

  • controlled all things that get you excited


Artery blood is high pressure

Pressure and speed drop when blood reaches capillaries due to them being small individually, however the total cross section of capillaries is larger

Venous blood is low pressure, but one way valves in the veins keep the blood going toward the heart

  • skeletal muscles help squeeze venous blood along