Questions for Further Thought
- We have discussed a variety of features of Ginkgo that might ally it phylogenetically with either the conifers plus Cordaites, or alternatively with Medullosa and the cycads. Now that you have studied both groups, what do you think? What kind of information might you need to tackle a question like that? What other characters may be helpful or homology of the characters we have the real problem?
- What does the association of Dadoxylon wood with both glossopterids (we'll see them in Lab X!) and Cordiates suggest about the evolution of this character? What does it say about the evolution of the two groups? Explain. HINT: Refer to the phylogenetic interpretation available on the Virtual Paleobotany Lab Directory Page as you think about this question.
- List synapomorphies for the conifers. Can you think of any really good ones? If not, how can we say that conifers make up a monophyletic clade? Consider that this lineage, along with modern Ginkgo has suffered a lot of extinction (lost a lot of its former diversity). How might this influence our phylogenetic reconstructions? What can we do about this problem?
- In the conifers (and some other groups like the early seed plants) we notice that by the time the group enters lowland depositional environments, the lineage is well-defined with many derived traits. Presumably, early evolution of the lineage has gone on in the "uplands" outside of our preservational window. What does this observation say about the evolutionary role of the lowlands, about which we know so much?
[Geologic Time Scale]