HONR219D Due 3/29/16 Homework VI

Transcription

1 Part 1: Yet More Vertebrate Anatomy!!! HONR219D Due 3/29/16 Homework VI Part 1 builds on homework V by examining the skull in even greater detail. We start with the some of the important bones (thankfully few) that you actually need to recognize. We ve already examined the tooth bearing bones, and opercular series. Now let s look at the major bones of the dorsal surface of the dermal skull roof. Pictured are: Osteolepis, a classic aquatic sarcopterygian Panderichthys, an aquatic sarcopterygian with adaptations for shallow water. Ichthyostega, a mostly aquatic sarcopterygian with the ability to come onto land Paleoerpeton, a tetrapod. Some midline skull roof bones are visible in all of them: Parietals, which enclose the parietal foramen (the vertebrate third eye. ) Postparietals, located posterior to the parietals. Tabulars, which form the posterior corners of the skull roof and touch the postparietals. Some skull roof bones are visible only in the fully aquatic ones: Opercular series Extrascapulars bones that attach the pectoral girdle to the skull Others aren t clearly recognizable in Osteolepis but take on identity in some of the others: Frontals anterior to the parietals Nasals anterior to the frontals and near the external nostrils.

2 1. Judging from the figure above, what changes occur in the relative length of the front and back of the skull during the transition from water to land? 2. Osteolepis and Panderichthys clearly possess an opercular series, and Paleoherpeton clearly does not. Identify, circle, and label the remnant of the opercular series in Ichthyostega. 3. The image at right shows the skull of Protocaptorhinus, a Permian age sauropsid. Identify and label the following elements in at least one each of the drawings: - premaxilla - maxilla - parietals - frontals - nasals For 2 pts extra credit, are postparietals or tabulars present? If you think you see either, label them. Skull openings: There are some of these that all bony vertebrates have: Nares (sing. naris) for the nostrils. Orbits for the eyeballs. These are clearly visible in Protocaptorhinus above. Others only occur in some groups: Supratemporal fenestra paired openings in the skull roof behind the orbits Infratemporal fenestrae paired openings in lateral surface behind the orbits. Antorbital fenestrae openings in the side of the snout Mandibular fenestrae openings in the side of the jaw.

3 4. The sketch at right by Evan Dahm shows the skull of the dinosaur Allosaurus in an oblique view. In it, identify and label the following: - Naris - Orbit (careful!) - Antorbital fenestra - Supratemporal fenestra - Infratemporal fenestra - Mandibular fenestra These openings may or may not be present in a given vertebrate. If present, they may have combined with other openings or been modified in other ways. Sometimes, their homologies can be truly difficult to decipher. 5. In the image of the skull of the mosasaur Clidastes at right, skull roof bones are white or light gray and internal braincase elements are dark. See how many of the openings discussed in Q 4 you can identify. Which are absent? For 2 pts extra credit, how has one of the openings been significantly modified from its ancestral form (like shown in the example)?

4 To understand a skull s anatomy, you have to look at it in ventral view. A palatal view shows the skull with the lower jaws removed. For example, the palatal view of Crassigyrinus. This reveals: Ventral edges of the bones of the skull roof. (Like the maxillae and premaxillae.) Midline bones of the braincase Paired bones that from or around the palatoquadrate. (Shaded in.) Two of interest: Pterygoids: (dermal) cover much of the surface of the palate and enclose a midline space that can be narrow or wide. Quadrates: (endochondral) form the knobs to which the lower jaw articulates. Together the palatoquadrate bones and the skull roof enclose subtemporal fenestrae meat-holes through which the muscles that close the jaws pass. In palatal view, one often glimpses the inner surface of the bones of the skull roof through various openings. 6. At right is the palatal view of the early amphibian Nigerpeton. Identify and label its: Quadrates Pterygoids Braincase elements Subtemporal fenestrae Be careful. The exact shapes and proportions of these elements are slightly different than in the example above, but the basic geometry of the skulls is similar.

5 Part 2: Consensus in cladograms. Now we return to phylogenetic systematic methods to address a problem. Often, a parsimony analysis will identify more than one most parsimonious tree. It frequently happens that there are too many of these to be able to describe or even talk about them all. When that happens, we need a way of presenting a synopsis of the information that they contain. We do this by means of consensus algorithms, whose results are given as consensus trees. In the example above, three trees have identical numbers of steps but tell subtly different stories of evolution. We can t convey all of that information in one cladogram, but we can convey the parts on which the three trees agree, using a consensus tree like the example at right. This tree reflects the facts that: In all the trees, B, C, and D are closely related. A always branches toward the bottom of the tree E shows up all over the place. But the problem: There are different methods for producing these. In the following questions, you will explore them. Strict consensus: If you want to be absolutely rigorous about it, you would use the strict consensus method. A strict consensus tree shows only the monophyletic groups that appear in all of the most parsimonious trees. 7. Your first task is to figure out what those are. So first, identify the monophyletic groups occurring in each tree using the following simple shorthand. Tree one is already done for you: Tree one: (A, B, C, D, E) (B, C, D, E) (C, D, E) (D, E) Tree two: Tree three:

6 8. Circle or indicate the monophyletic groups that appear in all three trees. Now draw a cladogram showing only the groups that you circled. Anything else must be shown as a polytomy. (If, for example, the only group that the trees had in common were the in-group, you would show A E emerging from a basal polytomy.) Majority Rule consensus: If you are willing to sacrifice a little rigor in order to preserve information, you can use the majority rule consensus. 9. Step one: Refer back to your list of monophyletic groups in question seven. For each one, indicate the percentage of trees in which it was found. (Should be 100%, 67%, or 33% in each case.) 10. List only the monophyletic groups that appear in at least 50% of the trees. Now, draw a consensus tree showing the groups on your list. Next to each node, indicate the percentage of trees in which it occurs. (Hint: You should end up with one polytomy somewhere.) Extra credit 5pts. Was the consensus tree example given above generated using either the strict or majority rule method?