BI 151 Biological Reasoning
Skeletons - Similarities
Consider the uses of teeth in catching and killing prey, cutting tough plant material, grinding hard seeds or nuts, etc. Look at
the teeth in the three jaws provided in lab. These are also shown below. What kinds of food do you think were eaten by each
skeleton's former owner? Justify your answer based on what you observe about their teeth. (It may be pretty easy to figure out what the
organism is. Don't base your explanation on what you know the critter eats -- base it on what you see in its teeth.)
Organism 1
Type of Foods Eaten: _____________________________________________
Explanation based upon observations of teeth:
Organism 2
Type of Foods Eaten: _____________________________________________
Explanation based upon observations of teeth:
Organism 3
Type of Foods Eaten: _____________________________________________
Explanation based upon observations of teeth:
Can you tell anything about organisms’ intelligence, eyesight, or behavior by looking at skeletons? Take a look at the opossum’s skull
and the raccoon’s skull below and in the lab.
The skull on the left is an opossum's in each case; on the right is the skull of a raccoon. The cranium, which is the bony case
that encloses the brain, is toward the bottom in the two lower pictures. (Jaw muscles pass through the opening between the
cheekbone and the skull, through which you can see the edge of the lower jaw in the pictures.)
Considering that these animals are approximately the same size and weight, what can you infer about their relative intelligence
from looking at their skulls?
Explain.
Now have a look at the "hand" (manus, to be more technically correct) of the bat and the macaque (an Old World
monkey). The manus is the appendage on the end of the forelimb -- a "front foot" in the macaque, or most of the wing of
the bat. Let's see if a specific similarity in these is due to homology or analogy, using the procedure you've gone through
before (see Homology/Analogy flow chart to review).
Consider the following structural similarity:
Each manus has five digits ("fingers").
What is the function of the manus in each organism?
bat:
macaque:
Is the specific similarity described above (that is, having precisely 5 digits, not 4, 6, or some other number) necessary in order to serve
the functions? Explain.
What do you conclude? Is the structural similarity I described above explained by homology or analogy? Explain.
What if the structural similarity had been described as "the manus in the bat and the macaque both contain long, slender bones"?
Would you have reached the same conclusion (homology or analogy) about that similarity as you did for the one above? Why or why
not? Explain fully, using the flowchart steps as above.
Each person should write a single statement that result s from these observations and conclusions about the bat and macaque.
Discuss these in your groups, and be prepared to discuss them in class.