MARY Continued

probably served multiple purposes, such as protection, courting, intraspecific competition, and thermoregulation. Feeding was accomplished mostly through low-level grazing and browsing. Some specializations of skeletal features, such as deeply inset teeth, large hyoids, and expanded hindgut regions, meant that some thyreophorans were capable of processing huge amounts of food. Locomotion is little understood because of the scarcity of thyreophoran trackways, which means that hypotheses about social behavior are also based on limited data sets of body fossil information. However, the co-occurrence of remains of more than one individual in the same deposits, such as the Late Jurassic stegosaur Kentrosaurus and Late Cretaceous ankylosaur Picanosaurus, suggests that at least a few thyreophorans lived in social groups.

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1. What would have been a defensive disadvantage for Stegosaurus other stegosaurs if their tail spikes had pointed upward (vertically) rather than outward (horizontally)?

2. The author states that ankylosaurs probably weighed more per volume than other dinosaurs because of their armor. For example, Ankylosaurus is estimated to have been about 10 meters long and weighed about 4 tonnes. How would you calculate an estimate of its density versus that for a 10-meter long ornithopod (which did not have any body armor)? What information would you need first before attempting to calculate such an estimate?

3. What independent information besides functional morphology would be required to convince you that ankylosaurids used their tail clubs as weapons for either interspecific or intraspecific combat?

4. Examine Tables 12.1 and 12.2 and represent in a bar graph the number of genera that occur within each of the following time divisions: Early Jurassic, Middle Jurassic, Late Jurassic, Early Cretaceous, Late Cretaceous.

a. What general trend in changes of thyreophoran diversity through time can you hypothesize on the basis of these data and the bar graph?

b. Compare the number of genera in each time interval versus place (region of the world). Do any biases in both time and place emerge from such an analysis?

c. What are possible sources of error in your analysis?

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