Homework 3. Due Friday Feb 13, by noon.
1. Go back to
Kevin Padian's testimon regarding homology, tasmanian wolves, kangarroos, etc.
Based on the traits presented, draw a phylogeny that shows the relationship between N. American
wolves, dogs, tasmanian wolves, kangaroos, and oppossums. On the phylogeny,
mark and label the appropriate branches with synapomorphic characters that
unite subgroups. Include the cranial traits (for example, a) # of molars; b)
presence/absence of palatal holes; c) reflected lamina; # of pre-molars; d)
presence/absence of ear bulla; e) presence/absence of para-occipital process;
f) carnassial teeth; g) position of lacrimal bone), presence of placenta, and
"overall dog like morphology" that Pandas focused on.
2. The following questions refer to the squirrel
article by Mercer et al.
In class we'll cover: What data were used to estimate the
squirrel phylogeny? ; In figure 1, which branch do we have the least confidence
in? Which one(s) do we have the most confidence in?
- In
figure 2, how did the authors determine the timing (in years (Ma) before
present) of branching events? [hint: molecular clock]
- Aplodontidae
(Mountain Beaver, found only on the PNW coast) is not a squirrel. Why was
it important to include it in the phylogeny?
- Do the
results support the traditional claim that flying squirrels form a group
relatively distant from all other squirrel lineages?
- Bishop
thinks that the congruence of major diversification events and major
changes in sea-level or formation of land bridges is remarkable. One
reason is that this congruence required agreement of several independent
types of data: 1) Identifying the nature and timing of
geological/sea-level changes based on the geologic & biological (non-squirrel)
record; 2) The branching pattern of the phylogeny, based on three
different genes; and 3) the calibration of time and DNA substitution rates
using fossil squirrel ancestors (note, this last item really requires
several independently collected types of data – fossil position in
geologic record, radiometric dating of fossil age, and DNA substitution
rates on each branch).
Questions : 4a) What do these congruencies suggest about factors affecting
squirrel diversification? (for example, are they causal or just
correlated? If causal, how?) Your answer should refer to figure 3 as an
example.
4b) What does this study suggest about scientist's ability to reconstruct
pre-historical events? [Hint, apply the 7 criteria for supporting
scientific theories or hypotheses, except ones that don't seem to apply].