Phylogenetics. Answers
1. (2 pts) The node marked
with a single asterisk represents the most recent
common ancestor of A and
B; the node marked with
two asterisks represents
the most recent common
ancestor of A, B and C.
2. (5 pts) Identify the nontrivial clades by circling the
appropriate nodes.
3. (2 pts) Among the tip
taxa, identify sister taxa in
addition to A and B.
D and E.
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4. (4 pts) Consider the mammalian cladogram below. Indicated are the following: Class Mammalia, which is divided into Prototheria (monotremes) and Theria (mammals
that bear their young alive), and Theria, which is divided
into Metatheria (marsupials) and Eutheria (placental
mammals). Indicate on the diagram, appropriate outgroup(s) for Eutheria and Theria.
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Trait
Species
A
B
C
D
1
+
+
+
+
2
+
+
3
+
+
+
+
4
+
+
+
+
5. (6 pts) Assuming that characters 1, 3 and 4 are ancestral, and bearing in mind that characters can be lost as
well as gained, draw two phylogenetic trees. Indicate on
each where traits are acquired and lost.
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6. (3 pts) Draw an additional tree assuming that characters
1, 3 and 4 are not ancestral.
4
7. (6 pts) Suppose now that you have an outgroup, O, for
which characters 1-4 are present. Further assume that the
outgroup is distinguished by a fifth character not found in
species A-D. Assume that trait 5 is derived. Draw two phylogenies corresponding to your answers to Question 5
above. Which is most likely? Why?
If independent character acquisition less likely than
loss (trait 2), bottom tree more likely. Otherwise you
can’t say.
5
8. (4 pts) Assume that none of the “trait absent” characters
in the table below reflect evolutionary reversals. Draw a
phylogenetic tree. Which characters is (are) ancestral?
Trait
Species
Platypus
Echidna
Kangaroo
Dog
Lemur
Four
Limbs
+
+
Live
Birth
-
+
+
+
Milk
Pouch
+
+
-
+
+
+
+
+
+
+
-
Here are two equivalent representations of the
same phylogeny. “Four Limbs” and “Milk” are ancestral. The other traits are derived.
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9. (6 pts) Historically, terrestrial vertebrates were divided
into four classes: Amphibia, Reptilia, Mammalia and Aves
(birds). Below is a cladistic analysis that accords with the
fact that birds evolved from small, carnivorous dinosaurs. The four vertebrate clades are shown in blue and
their division into more familiar groups in black at the
right. a. What are Tuataras and squamates. b. Which of
the familiar groups are “reptiles?” c. If we lump these
groups together, resulting class, Reptilia, is paraphyletic.
Explain why. Be specific.
a. Tuataras (Rhynchocephalia) are superficially
lizard-like animals, the only living species being restricted to islands off the New Zealand
coast. Distinguishing synapomorphies involve
tooth morphology including the fact that the
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teeth are fused directly to the jaw as opposed
to being set in sockets. Squamates are lizards
and snakes.
b. “Reptiles” consists of crocodiles, tuataras,
squamates, turtles.
c. As indicated in the figure, Reptilia doesn’t include the descendant clade Aves (birds).
10. (6 pts) Three of the evolutionary trees below are
equivalent. Which is different?
Number 3. In 1, 2 and
4, F and G are sister
taxa. In 3, G and E are
sister taxa.
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