LECTURE 20 STUDY GUIDE (AMNIOTES)

what is amniote?

tetrapods that develop from an amniotic egg

which three groups of vertebrates are amniotes?

reptiles, birds, and mammals

amniotes fall within one of three lineages: diapsid, synapsid, or anapsid? how do these lineages differ?

the three groups are recognized based on openings in the skull near temples

synapsids include mammals

diapsids include all reptiles and birds

anapsids include turtles

why was the amniotic egg so significant in animal evolution?

decouples reproduction from water and enabled amniotes to stray far from water

what are the four extra-embryonic membranes and what are their locations and functions?

1. amnion: surrounds the embryo and amniotic fluid that cushions and protects the embryo

2. yolk sac: surrounds an embryo’s primary food called yolk; proteins and lipids produced by moms liver

3. allantois: reservoir for metabolic wastes and may be used in gas exchange along with the chorion

4. chorion: envelops the embryonic mass isolating it from egg albumen in shelled eggs; exchanges gases

how do the eggs of oviparous amniotes differ from ovoviviparous amniotes?

oviparous amniotes secrete significant amounts of albumen (egg white) and a leathery or calcareous shell around their eggs to offer additional nutrients/protection respectively

ovoviviparous amniotes give live birth

what is incubation?

act or process of an amniote mother sitting on her eggs to keep them warm to allow them to hatch

why might oviparous amniotes incubate eggs?

to regulate the eggs temperature to prevent them from variable temperature

what important population-level variable is influenced by incubation temperature in some reptiles?

sex ratio

in most, what is the ribcage used for?

to ventilate the lungs

turtles do not ventilate their lungs through their ribcage, why?

turtles have their pectoral and pelvic girdles within their ribcage

their ribs flatten and fuse to form the basal layer of the dorsal carapace and a superficial layer of dermal scutes later forms the visible portion of the shell

when they inhale, they expand their body out of their shell

when they exhale, they contract viscera against lungs

describe the changes in amniote skin

skin became keratinized to reduce water loss

various epidermal modifications evolved: reptiles —> scales; birds —> feathers; mammals —> hair

how many heart chambers do amniotes possess?

reptiles possess three chambered heart

crocodilians, birds, and mammals have four

what is the general blood circulation for a non bird reptile?

systemic tissues —> systemic veins —> right atrium —>ventricle —> pulmonary arteries —> lungs —> pulmonary veins —> left atrium —> ventricle —> left systemic aorta —> systemic arteries —> systemic tissues

what is the gas exchange circuit called in amniotes?

pulmonary circuit

some reptiles that dive beneath water for extensive periods have a modified cardiovascular system. what is this modification?

may use a cardiac shunt when diving which means blood is shunted away from pulmonary circulation by diverting it into the right systemic aorta (purple vessel)

what is ectothermic?

must acquire extrinsic heat by basking in the sun and must shade to cool themselves (non-bird reptiles)

what is endothermic?

derive heat intrinsically from metabolism of food

meaning they usually eat more (birds and mammals)

what is poikilothermic?

have highly variable body temperature (non-bird reptiles)

what is homeothermic?

regulate body temp at a set point via homeostasis (birds and mammals)

which three forms of nitrogenous waste do amniotes excrete?

1. urea [(NH2)2CO2] —> usually in mammals

   1. medium complexity

   2. medium toxicity

   3. medium amount of water

2. uric acid (C5H4N4O3) —> birds

   1. most complex

   2. least toxic

   3. requires least amount of water

3. ammonia (NH3/NH4+) —> aquatic forms (fish)

   1. less complex

   2. toxic

   3. requires a lot of water

the mojave desert has numerous non-bird reptiles. considering what you now know about amniotes, which adaptions do mojave non-bird reptiles possess that enable them to be so successful in such a forbidding habitat?

most of the non-bird reptiles excrete uric acid because it requires less water