Review Questions for Biology 404

HOL Ch. 7: The Early Vertebrates

1. Represent the following groups on a cladogram, reflecting current views on their relationships as reported by Cowen: cephalochordates, urochordates, craniates, vertebrates, hagfish, and chordates. Some of these are higher taxa that include others as members. Where do lampreys fit on this cladogram?

2. What are some shared-derived features (synapomorphies) of the following groups? 1) Chordata; 2) Craniata; 3) Vertebrata.

3. Conodonts are used extensively as guide fossils in stratigraphic characterization of the Paleozoic Era. What are they? For examples, see the following websites:

4. What potential advantage did early vertebrates, like ostracoderms, gain by using phosphate, instead of the more common mineral calcite, in their skeleton?

5. Why is the conventional grouping, "agnathans," no longer used by most systematists?

6. Compare and contrast the following "ostracoderm" vertebrates: the Ordovician astraspid, Astraspis, the Devonian heterostracan, Pteraspis, and the Late Silurian osteostracan, Hemicyclaspis. See the HOL Ch. 7 website for more details.

7. Jaws are thought to have evolved from what structures? How were these structures originally used before they were jaws? What is the clade of all jawed fishes and all their descendents (including humans)?

8. Compare/contrast the following jawed fish groups: acanthodians, placoderms, and cartilaginous fishes. Dunkleosteus was a giant predatory placoderm. How did its jaws operate?

9. So-called "bony" fishes correspond to which named clade? Bones are not invented by the ancestor of all bony fishes, because other jawed fishes have bony coverings. The technical synapomorphies for the bony fish clade include: endochondral bone, lepidotrichs on fins, jaws lined by dentary, premaxillary and maxillary. Characterize the two major subclades of bony fishes, the rayfins and lobefins. Name three groups of lobefin fishes, not including the terrestrial members of this clade (including humans).

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