1. Dr. Cowen is clearly a "clade thinker" but I am more "cladistic" than him in my terminology for these early tetrapods. He still is using a more traditional "grade" terminology of: fish -> amphibian -> reptile -> mammal or reptile ->bird which, in my opinion, has subtle impacts on how one thinks about the relationships among living terrestrial vertebrates. True, early vertebrates were clearly "amphibians" in terms of their dependence on aquatic habitats for reproduction but, as Dr. Cowen points out, most of these early tetrapods more closely resembled lizards in their appearance and life mode than they did salamanders or frogs. One problem is, the novelty that clearly unites living members of the amniote clade (reptiles + mammals), the amnion, is a soft part feature that is not preserved in the Paleozoic tetrapods. The amnion is clearly associated with terrestrial, not amphibious, reproduction, but we are not really sure when it evolved. This is because most of these early tetrapod lineages are extinct. So what would I differently than Dr. Cowen? I would prefer to emphasize clades (surprise?) because those are the only groups that we have can claim to have evidence that they really exist or existed in time and space. The evidence we have is shared novelties, e.g., tetrapods share four limbs, and amniotes share an amnion. In contrast, amphibians are no different than saying all tetrapods that lack an amnion. So I would prefer to use the terminology of "early tetrapods" rather than "amphibians."
So the question here is, can you organize the following tetrapods into a cladogram based on the material presented in Ch. 9?
There will almost certainly be a question on the next quiz that depend on your ability to "clade think" in this way. The tetrapods are:
Living: salamander, frog, lizard; Extinct: Ichthyostega, the temnopondyl Cacops, the anthracosaurs, Diplocaulus and Seymouria. Combine all of these into a single cladogram.
Extra challenge #1: add microsaurs and Westlothiana ("Lizzie").
Extra challenge #2: specify novelties that provide evidence for the basal (lower) nodes on your cladogram. This web link on Seymouriamorpha may help here, because Dr. Cowen does not really get into the technical details of skeletal novelties used by paleontologists.
2. What were likely habitats for early reptiles?
3. How is the amniote egg analogous to a space ship? How does the contrast between the amphibious eggs of frogs and salamanders, and the amniote eggs of lizards, affect the mode of fertilization?
4. According to Dr. Cowen, why were most early terrestrial vertebrates and arthropods predators, rather than herbivores, when so much plant material was available? What does this have to do with symbiosis in animals?
5. What is an example of a large Paleozoic insect? How large did they get?
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