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UMD GEOL 104 - Homework 5: Dinosaur Physiology

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Name: GEOL 104 Dinosaurs: A Natural History Homework 5: Dinosaur Physiology DUE: Wed. Nov. 28 Part I: Growth Rates The curves above represent the body mass (in tons) of the giant crocodylian Deinosuchus (line A) and the ceratopsian Triceratops (dashed line B), both of which are found in the Late Cretaceous deposits of the American West. 1) At what age does Triceratops growth slow down? 2) At what age does Deinosuchus growth slow down? 3) Which of these reptiles grew at a rate more like a modern mammal (i.e., fast)? [ Triceratops | Deinosuchus ] 4) Typical modern large mammals have lifespans of many decades. Which of these Cretaceous reptiles had a mammal-like lifespan? [ Triceratops | Deinosuchus ] Part II: Predator-Prey Ratios Robert Bakker has suggested that we can use “predator-prey” ratios to test if an extinct community were primarily endothermic, primarily ectothermic, or somewhere in between. The ratio (represented as the percentage of the total biomass made up of carnivores) would have higher values for ectotherms (with their lower food requirements) and lower for endotherms (which need to eat constantly in order to fuel their bodies). Based on theoretical and observational data, ectothermic communities should have predatory-prey ratios over 20%, while true endotherms should be below 7%. 1Name: Below are values Bakker discovered for various assemblages (from particular formations or localities) of fossils (and one modern: the Serengeti). These are arranged by the Amniote Radiation in which they occurred. Basal Synapsid Communities Therapsid Communities Crurotarsan Communities Locality Pred/Prey ratio Locality Pred/Prey ratio Locality Pred/Prey ratio Williams Ranch 26% Tapinocephalus zone 12% Er-Ma-Ying 15% Black Flat 28% Daptocephalus zone 13% Ischichuca 17% Dinosaur Communities Mammal Communities Locality Pred/Prey ratio Locality Pred/Prey ratio Morrison 3.5% Wasatch 4.4% Cloverly 3.7% Chadron 5.4% Dinosaur Park 3.5% Harrison 4.3% Hell Creek 1.9% Serengeti 0.3% Mammals are known to be endothermic. Essentially all researchers agree that basal synapsids were ectothermic. 5) The values for the dinosaur communities are [ like basal synapsids | like mammals | intermediate ]. 6) The values for the crurotarsan communities are [ like basal synapsids | like mammals | intermediate ]. 7) The values for the therapsid communities are [ like basal synapsids | like mammals | intermediate ]. Part III: Dinosaur Respiration (Lungs) Food is only part of metabolism. Another important aspect is respiration: without oxygen, there isn’t much metabolism!! Recent work by Colleen Farmer, David Carrier, and Elizabeth Brainerd on modern animals have revealed a lot more diversity in vertebrate respiration than previously known. For example, mammalian breath (which uses the ribs plus a muscular diaphragm, but doesn’t use a throat pump) is just plain weird! Here is a look at some of the techniques used to get air down into the lungs: • Buccal pumping (swallowing air): used by air-breathing fish and amphibians • Gular pumping (using an actively pumping throat): used by advanced lizards • Costal breathing (moving ribs in and out): all tetrapods but ribless frogs and shelled turtles • Diaphragm breathing: mammals • Hepatic piston (liver pumping): crocodilians • Air Sac pumping: birds Interestingly, both crocodilians and birds use their pelvic (hip) muscles in breathing. In the figure on the previous page, A is a modern alligator. When the rectus abdominis muscle 2Name: contracts it pulls the pubis forward, pushing the liver forward and forcing air out of the lungs (expiration). When the ischiopubic and diaphragmatic muscles contract, it pulls the liver backwards, causing the lungs to expand and draw in air (inspiration). B shows respiration in a pigeon. During inspiration the sternum rotates downward and the longissimus dorsi muscles contracts to pull the tail up: together, these inflate some of the air sacs in the body. During expiration the infrapubic and suprapubic abdominal muscles contract to pull the sternum up and the tail down, pushing air out of the sacs. Below is a drawing showing the air sac system of a bird, in left lateral view. C, I, AT, PT, and AB are different individual air sacs—you don’t need to worry about that level of detail. The bold arrows show how the air sacs invade the vertebrae: Farmer and Carrier have extrapolated back to suggest the following as the ancestral breathing condition for archosaurs (that is, the condition in the common ancestor of birds and crocodilians). To the left below is the primitive archosaur EupAs the ischiotruncus muscle contracts, it pulls the gastralia (belly ribs) down, which would expand the lungs. It seems that such a mode of breathing might be possible for primitive theropods. To the right is thehypothesizedarkeria. breath cycle for Allosaurus. 8) Dinosaurs tend to have long pubes and ischia for archosaurs. How might these skeletal changes be related to an increased lung capacity? 3Name: 9) Ornithischian dinosaurs lack gastralia. Would it be possible for them to use the ancestral archosaur mode of breath? To the left are the pelves of some advanced ornithischians, so that the pubis (or the pubis plus ischium) can move relative to the ilium. 10) A is the pelvis of Triceratops in left lateral view. Like other ceratopsids, but unlike more primitive ceratopsians and most other ornithischians, the pubis and ischium can move together as a unit. As the rectus abdominis (RA) muscle contacted, it would have pulled the pubis and ischium forward; as the ischiocaudalis contracted it would have pulled the two bones back. This motion is most similar to the breathing system in [ birds | mammals | crocodilians | ancestral archosaurs ]. 11) B is the pelvis of the hadrosaur Corythosaurus. Its pubis (like those of many advanced ornithopods) was able to rotate slightly outward. When the iliopubic muscle would contract, the pubis would move slightly to the sides. On the drawings to the left, label which of the two dorsal (overhead) views shows the pelvis during inspiration, and which in expiration. 12) Other than advanced ornithopods and ceratopsids, the pelvic elements of ornithischians are immobile. If mobile pelvic elements exist to help increase the oxygen


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