II. Short answer. Your answers will be graded based upon whether they are factually correct and complete. (worth 5 points each unless otherwise noted)

1. Describe the heat gain and loss experienced by this mouse sitting on a large rock. In which direction(s) does the heat move and by which mechanism(s) (e.g., conduction, convection, radiation). Assume the following:

(1 point each up to 5 points, 1/2 for correct direction and 1/2 for correct mechanism)

Heat moves from

2. Compare and contrast the dentition and digestive system of a ruminant herbivorous mammal with that of a myrmecophagous (ant-eating) mammal. Why are they so different?

For herbivory (2 points total), the following were worth 1/2 point each for up to 2 points:

For myrmecophagy (2 points total), the following were worth 1/2 point each for up to 2 points:

Herbivores have evolved a long, complex digestive tract because plant material is harder to digest than animal material. The teeth are necessary to break up the plant material to increase its surface area so that it can be broken down by the microbes in the herbivore’s digestive tract. In myrmecophagous animals, the long tongue and enlarged salivary gland helps capture insects in their burrows, lack of teeth means that another mechanism is needed, which led to the evolution of the roughened stomach. (1 point)

3. Describe at least three ways in which choriovitelline and chorioallantoic placentas differ in structure. How do these differences affect nutrient transfer and gas exchange, and the degree of infant development at birth?

(1 point) Choriovitelline placentas have fusion and vascularization of the chorionic and vitelline (yolk sac) membranes, while Chorioallantoic placentas have fusion and vascularization of the chorionic and allantoic membranes.

(1 point) The surface of the Choriovitelline placenta is convoluted for greater surface area, which allows some diffusion of gases and nutrients. The surface of the Chorioallantoic placenta has villi (tiny projections of the chorion) that work their way deep into the uterine lining. This allows closer proximity between the maternal and fetal circulatory systems, so there is more diffusion of nutrients and gases across the placenta.

(1 point) The yolk sac of the Choriovitelline placenta is very large and contains most of the nutrients needed for the development of the fetus, while the yolk sac of the Chorioallantoic placenta is much smaller and only provides nutrition for the first days or weeks of development.

Other acceptable answers:

CV has shell membrane (made of keratin) that protects the embryo from the mother’s immune system, while CA has a well-developed trophoblast layer that is a physical and chemical barrier against the mother’s immune system.

(2 points) The choriovitelline placenta is not as efficient as the chorioallantoic placenta for gas and nutrient exchange, so infant metatherians have to rely on the yolk sac for almost all their nutrients and cannot stay in utero long enough to be well developed at birth.

4. Describe, compare and contrast the alternative reproductive strategies of delayed implantation, delayed development, and embryonic diapause. In what kinds of environments or situations would you expect to find each type of strategy?

(1 point) Similarities: They all involve a pause in the development of the embryo, after which development eventually resumes after a period of days to months.

(1 point) Delayed implantation involves a pause after the embryo has divided a bunch of times, but before it has implanted in the uterus of a placental mammal. It occurs when environmental conditions are somewhat unpredictable or out of sync with the gestation period (this allows the birth to occur at the best time for offspring survival).

(1 point) Delayed development involves a pause in development shortly after implantation. It occurs in similar situations as delayed implantation.

(1 point) Embrionic diapause involves a pause in development at a time similar to delayed implantation, and occurs in metatherians that are already suckling older offspring. When the older offspring die or are weaned, the embryo resumes developing.

(1 point) Delayed implantation and delayed development occur in eutherian (placental) mammals, while embryonic diapause occurs only in metatherians (marsupials).

5. Describe 5 morphological specializations that increase stride length or stride rate. Be sure to include an explanation of how and why these specializations affect stride length or rate.

1 point each (up to 5)

Increasing stride length 


Increasing stride rate 


6. Describe at least five specialized structures of the face, cranium, and pinnae that have evolved in echolocating bats. For each structure, how does it function in sound production or sound reception?

1 point each (1/2 for feature, 1/2 for function) up to 5 points; must have at least one structure from each category for full credit, otherwise -1/2 point

7. This diagram shows rates of oxygen depletion and carbon dioxide accumulation in relation to the levels needed to maintain consciousness and trigger the urgent need to breathe in diving humans. How might the location and slopes of these lines differ for diving marine mammals such as whales and dolphins? What physiological mechanisms account for these differences and the ability of marine mammals to stay submerged for long periods of time? (worth 10 points)

Changes to the diagram might include (1 point each up to a maximum of 5 points):

Adaptations that might account for these include (1 point each up to a maximum of 7 points):