Actually, whales are an excellent example of why molecules
and fossils go together. Molecular sequences, of course, can only
be obtained from living species, meaning those 90 or so living species
that are the end members of a huge number of fossil species representing
either other extinct clades or ancient members of extant
clades. The molecules can never get us any resolution of the
topology of the real tree of whales because they do not include
fossils. For whales, this is critical because the extinct group we
used to call archaeocetes go unrepresented in the molecular phylogeny--a
mere 30 or so million years of pre-Miocene history including the taxa
that entered the sea. Molecular phylogenies of whales help a
lot but it's only part of the story, and a fairly incomplete part as
well. Fossils and morphology complete the picture but even
then it remains unresolved at detailed levels. So molecules often
can get us an overview of phylogeny but fossils can show what really
happened (and of course combined with lots of good geology,
paleoenvironmental analysis, functional analysis, etc, can sometimes tell
us why it happened). No good paleontologist will reject
molecular data but will add it to his/her data bank as a possible means
to test their own hypotheses.
So Tom you should get your students to compare both a morphological
phylogeny and a molecular one, using for the first many of the fossils
and for the second all the molecular data. That will help them to
understand how different disciplines working somewhat independently but
ultimately together come to more substantial conclusions than either
working alone.
Unfortunately the thread you asked about includes too much bitching about
single hypotheses developed along the way. This is a dynamic
field now, and we will soon, or should, see combined data that will give
us a much better picture.
I don't think your class really needs to read the tread here--you
have an excellent plan as it is, and the tread is not representative of
paleontology or molecular biology in general anyway.
Jere
At 07:28 PM 9/12/02 -0400, you wrote:
>I'm teaching a high school elective that compares the paleo record of
whale
>evolution with that yielded by mtDNA sequences. Students study
modern whale
>bones, examine an Oligocene mysticete in a nearby museum, use online
and
>literature sources for paleo data, and isolate mtDNA (chicken proxies
for the
>techniques), run PCR reactions, manually sequence mtDNA fragments,
and use
>Genbank sequences for aligning and building trees.
>
>I'd be grateful if someone could email the full thread (to date) of
this
>discussion on paleo and molecular data (to me, not the
listserve). Even if
>the discussion is occasionally overheated, it will illustrate to
students the
>tension that arises from using different data sets to resolve a
single
>problem.
>
>Tom DeVries
>