Download Comparative Anatomy - 2nd hour exam November 19, 2001

Comparative Anatomy -
2nd hour exam
November 19, 2001
This exam is based on musculature, skin, digestive, respiratory and circulatory
systems and your answers should be based on these systems.
Answer 5 questions (20 points each)
1. Describe the major innovations, changes or advances in the evolution of the digestive
system and the reasons for them (if known).
major changes =
1. change from filter feeder Amphioxus and Agnatha - to jawed feeder on
meat = sharks, placoderms,
2. change from spiral valve intestine to either caeca system of teleosts or long
intestine of frogs up. no reason- just a new system.
3. Loss of gills (pharynx become less important)
4. development of gizzard and crop in birds and some reptiles - no teeth yet the need
to grind up plant food for digestion.
5. bacterial digestion - rumen in stomach or caecum.
6. devt of a cloaca in amphibia through reptiles - loss in mammals. function for
water reabsorbtion - loss to separate waste from reproduction.
2. What changes in the muscular system were necessary in the transition from water to
land (Fish to Amphibian)?
the word necessary is perhaps tricky.
1. - need better limb musculature
2. - need girdle musculature - propulsion in hind limbs, support of ribs and body in
front limbs. Result is a lot of ventral musculature in hind limbs, also in front
limbs but also dorsal musculature in front girdle = rhomboideus etc.
3. layering of hypaxial muscles to hold in the guts.
4. intricate attachment of epaxial muscles to vertebrae for better support.
5. beginning of muscles to back of head to hold it up.
6. additionally - loss of gill arch muscles - turn them into neck muscles.
3. Describe the relationships that exist between the circulatory system and the respiratory
system. How did changes in one system cause or require changes in the other?
1. major relationship is gill arches = aortic arches. Several when gills functional.
when gills lost - arches start to reduce in number until only one pair to lungs
and one arch to body. Flow counterflow design of gills
2. Second relationship is between gills vs lungs and heart structure.
when lungs develop, need;
a) new circulation to return lung blood to heart = pulmonary vein
b) beginning of separation of heart into left and right sides, one associated
with sending blood to lung, the other to the body.
c) this, in turn, requires the development of blood coming to the body to
come into only one side of heart rather than both sides.
d) devt. of lymph system to counteract pressure when you get rid of gills.
4. Haekel (sp.) is remembered for the statement "Ontogeny recapitulates Phylogeny." We
now generally view this statement as inaccurate. Give examples, based on
anatomy, to show where this statement has some validity.
the development of mammals most closely resembles the evolution of
mammals in the following examples.
1. heart- going from a single tube to a parallel system
2. posterior veins; going from a bilateral posterior cardinal system to
an adult single vena cava.
3. Aortic arches - going from a complete set of 6 to an adult mammal set of
1.5
4. cloaca in human embyos
5. yolk sac in human embryos.
Not all the in between steps are accurate, but in general form, ontogeny
recapitulates phylogeny in these systems.
5. We argue that animals cannot have structures "preadapted" for a future life if such
structures are not useful in their current way of life. Give some examples of
at least two cases where structures, developed for an earlier function (way of life)
proved useful later in evolution in a different way of life.
1. limbs for swimming in a swamp in crossopterygian fish prove useful in
coming out on land.
2. lungs - useful for breathing in low oxygen stagnant water are useful on
land.
3. hair - developed for sensory function - turns into insulation
4. feathers, developed for insulation - prove useful in flight.
5. jaws - first a simple way to close the mouth, prove useful in biting
things.
6. Discuss (with examples) the basis(es) of the observation that you cannot make sense of
some evolutionary changes by looking only at adult animals.
classic examples are evolution of the pattern of aortic arch coming from
heart in reptiles and mammals - can't derive one system from the other need the embryology to see how it occurred.
other examples - pattern of head circulation in rodents, pattern of posterior
veins in mammals,