Questions for Further Thought
- Many think that the solution to the problem in sorting out the relationships of angiosperms to other seed plants lies in finding their "ancestor" in the fossil record. Is this a reasonable approach? Explain. Do you see any potential problems?
- How could the paleobiogeography of early flowering plants help you in the search for a sister taxon for the angiosperms?
- Plot the character "wood-type" (character states: "manoxylic", "pycnoxylic") on the cladogram for the seed plants. Is the character homoplastic or homologous? What does this tell you about the evolution of wood?
- If the ovulate structures observed in a number of Mesozoic seed plants are not homologous, what can you tell about the evolution of this character?
- In 1969, Delevoryas found foliage morphologically identical to Glossopteris in the Middle Jurassic of Mexico. What possible explanations for this phenomenon can you think of? Keep in mind what the Glossopteris leaf type really stands for in terms of diversity!
- If the clade containing Caytonia and the corystosperms is sister to glossopterids, what can you tell about the age of the clade? Or if not, why not?
- As you've previously learned, many propose that the cycads originated from seed plants not unlike the medullosans based on the morphology of their megasporophylls. Bearing in mind that the glossopterids also have leaf-borne reproductive organs -- why are they not as likely ancestors to the cycads?
- Compare the cladograms of Crane (1985), Doyle and Donoghue (1993) and Nixon and colleagues (1994). How do they differ? How are they similar? What different characters does each use that lead to the differences in topology of the resulting trees? Which interpretation of relationships do you prefer? Explain.
- Within the anthophyte clade, there is significant homoplasy in the distribution of bisexual reproductive structures. Consider what is known about the developmental genetics of angiosperm flower development (e.g., Coen and Meyerowitz, 1991) and the kind of homeotic mutations that have been used to study these patterns. Speculate on a mechanism that could produce such variability in reproductive structures among the anthophytes.
[Geologic Time Scale]