Station 1
Fossils
Read “The Formation of Fossils” and “Law of Superposition.”
1. What is a fossil? How are fossils formed? Describe at least three different
types of fossils.
2. What is the law of superposition and how does it help determine the age
of a fossil? Can superposition alone tell us how long ago a particular fossil
formed? (Be careful.)
3. What information can we get from a fossil about the organism that left it?
For three of the pictures of fossils, give one observation about the organism that
left it and one inference.
Station 2
Trilobites
These trilobites were bottom dwelling aquatic organisms that are one of the
earliest complex life forms to appear in the fossil record. All trilobites are now
extinct. Examine these specimens and try to determine if you can observe any
changes in the body structure of trilobites between the Cambrian and the
Devonian. You might try to focus on eyes, segments, or increases in body armor.
1. What changes in body structure occurred in the history of trilobites?
2. Between the Cambrian and the Devonian the fossil record shows an
increase in possible predators such as fish. Do you think there is a
relationship between this and the changes we see in body structures?
Explain.
3. Look at the Cambrian trilobites. The body structure of these trilobites did
not change for 500 years. Does this mean that evolution was not
occurring? Was natural selection occurring? Explain.
Station 3
Hominid Skull comparison
Directions: Read the following excerpt. Examine the skulls of different
species paying close attention to how features amongst them compare
and contrast.
Examine the shapes and features of each skull. The structure of fossils
such as these skulls can show us similarities between different organisms.
When you compare skulls, notice how drastically different homo sapiens
(modern humans) are to Gorillas. Humans are more closely related to every
other species at this station than they are to gorillas. Examine the
phylogenetic tree of skulls and determine the relationships. Which skulls are
more closely related?
Gorillas have a large saggital crest (the ridge top center of their skull).
This feature is also present in the chimpanzee skull and Australopithecus
boisei to a lesser extent. Also notice how prominent the supraorbital ridges
(eyebrow sections) are in the gorilla and chimpanzee. As more speciation
events occur, these features become less pronounced. The canines in the
chimpanzee and gorilla are more pronounced than in the other species. You
may notice that humans, chimpanzees, and gorillas all currently live on our
planet, while the other species are extinct. It is important to remember that
these organisms did not evolve from one another. They speciated from a
common ancestor.
The following link provides an interesting look at the relatedness
of different species closely related to homo sapiens.
http://humanorigins.si.edu/evidence/human-family-tree
Station 4
Radioactive Dating
One way (there are others) to date fossils is called radioactive dating, often done
with isotopes of carbon (then called carbon dating). Carbon usually exists as C12,
but there are some atoms of C with extra neutrons called C14. These carbon
atoms are radioactive—that is they emit these extra particles, or we say they
decay. The rate that they decay is known as the half-life. It is the time it takes
half the radioactive atoms to decay. (The half-life of C14C12 is 5,570 years.)
So, for example, an animal dies today; all of the C14 in its bones is still there.
100% is still present, or let’s say, 12g. In 5,570 years C14 = 50% or 6g. (The
other 50% or 6g has turned into C12.) In 11,140 years (2 ½-lifes) only 25% of
the original C14 or 3g will remain. Obviously, in really old specimen there are
very small amounts of C14 remaining, making accurate measurement more
difficult. Other isotopes have longer half-lifes and are used.
Example:
# of ½-lifes
Originally C14
Converted C12
Age (years)
0
12g
0g
0 (current)
1
6g
6g
5,570
2
3g
9g
11, 140
3
1.5g
10.5g
16, 710
Questions:
1. In a normal bone, there is 96g of C14. An archaeologist finds a bone and
determines there is only 12g of C14 in it. How old will she say it is?
2. A fossil tooth is dated to be 16,710 years old. It contains 13g of C14 and
91g of C12. How much C14 did it have originally?
3. You find a fossil clam. A laboratory determines its composition to be 6%
C14 and 94% C12. How old is it?
Station 5
Comparative Anatomy
Analogous Structures
Analogous Structures are those characteristics that are similar in function, but
different in structure. In these pictures (Foresman Book pp. 200-201), we see
butterfly wings and bat wings compared, along with squid eyes and human eyes.
1. Would analogous structures be used to indicate a common ancestor or a
different ancestor? Explain.
2. A common saying in biology is “Form Follows Function.” Use this to
explain why analogous structures might occur.
3. Are analogous structures a result of convergent or divergent evolution?
Explain.
Vestigial Structures
Read the section “Vestigial structures are clues to evolution origins”
(Holt Book p. 182).
1. What is a vestigial structure? What are some other examples of vestigial
structures in humans or other species?
2. Suppose you suspected that snakes descended from creature that used to
have four legs. What vestigial structures might you look for to support
your hypothesis? Would these prove you were correct?
3. Why are vestigial structures strong evidence for evolutionary
relationships?
Homologous Structures
Homologous Structures are structures that are similar in different species.
Examine the bones in the picture at the top of page 182 (Holt book). Notice the
similar position of like bones.
1. Describe the function of each set of bones below:
Animal
Human
Function
Whale
Bird
2. Are the bones arranged in a similar way in each animal? Explain.
3. Why do the same bones appear slightly different between the species?
4. What can homologous structures tell us about the relationships between
species?
Comparative Embryology
Embryonic development can give indications of how related some organisms are
to one another. Differences in genetic make up do not become apparent until
later in development. All of these organisms show gill slits and tails.
(See Foresman Book p. 202)
1. Which statement is most supported by this evidence?
a. Birds go through fish embryo stage followed by a retile embryo
stage before becoming a bird embryo.
b. Birds evolved first from fish and then reptiles.
c. Birds are more similar to retiles than to fish because they share
more similarities in genetic makeup.
2. In what way could you consider this as support for the theories, which
propose that birds arose from an ancient reptile-like animal (theocodont)?
3. What does comparative embryology tell us about relationships between
organisms?
Station 6
Comparative Biochemistry
There are many different species in the Ape family. These include the African
chimpanzees and gorillas as well as the Asian orangutans and gibbons. The only
current representative of the human family is Homo sapiens, although fossils of
other hominids have been found. We would like to analyze data to determine
the relationship of humans to these others.
1. Below are 2 diagrams showing the possible relationships between these 4
species. Draw at least 2 more that you think might be possible.
gorilla
human
Common
Ancestor
chimps
gorilla chimp
humans
Common
Ancestor
2. Modern research techniques allow biologists to compare the DNA that
codes for similar proteins to make predictions about the relatedness of
organisms. You have the following DNA strands: human, chimp, gorilla,
common ancestor. (Note: The data for human/chimp/gorilla is real. The
common ancestor is hypothetical, as no current DNA exists.)
Chimpanzee
Position 1
Position 20
A-G-G-C-C-C-C-T-T-C-C-A-A-C-C-G-A-T-T-A
Human
Position 1
Position 20
A-G-G-C-A-T-A-A-A-C-C-A-A-C-C-G-A-T-T-A
Gorilla
Position 1
Position 20
A-G-G-C-C-C-C-T-T-C-C-A-A-C-C-A-G-G-C-C
Common Ancestor
Position 1
Position 20
A-G-G-C-C-G-G-C-T-C-C-A-A-C-C-A-G-G-C-C
a. Compare the human DNA to the chimpanzee. Count the number of
bases that are not the same and record in the chart. Repeat with
human and gorilla.
Hybridization Data for Human DNA
Human DNA compared to:
Number of matches
Unmatched bases
Chimpanzee DNA
Gorilla DNA
Common ancestor DNA compared to:
Human DNA
Chimpanzee DNA
Gorilla DNA
Number of matches
Unmatched bases
b. How do the gorilla and chimp DNA compare with the human?
Which has more similarity? What does this suggest about the
relationship between these three?
c. Does this support any of your hypotheses from #1? Explain.