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How Do They Know That Dinosaurs Held Their Tails Erect? What's the Physics?


When you think of bridges, you probably don't think of a dinosaur. Did you know that the structure of a dinosaur can be compared to a bridge? When you built your "bridge" out of fettucini, you learned about how bridges can support weight. Now, we are going to see how this knowledge of physics can be used to discover the answers to other questions.

How do they know that dinosaurs held their tails erect? What's the physics?

When museums first began displaying dinosaur skeletons, they were assembled with their tails laying flat on the ground. Scientists now know that this design would make it impossible for dinosaurs to support their weight and walk or run with speeds estimated from the fossil record. Now it is believed that the tails served as a counterbalance. It has become commonplace to show bipeds such as Deinonychus (a Raptor such as those seen in Jurassic Park) as having a tendon-stiffened outstretched tail acting as a counterpoise and a horizontal backbone (see image). Deinonychus had a modified toe bearing a five inch sickle-shaped claw designed to gouge and slash its victims. That meant the animal had to stand on one leg while simultaneously grappling with a struggling prey. To balance like this, the rigid tail had to act like a built-in tight-rope walker's balancing pole (Desmond 77).

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Image of Deinonychus

Image of a suspension bridge.
Permission for use granted by Nova

Image of cable-stayed bridge.
Permission for use granted by Nova

Compare the images of Deinonychus and the bridges. Do you see any similarites in the structures?

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This activity has two parts. In the first part, students search Internet sources to develop background information. Students will list three reasons found in the sources below that support the arguement that dinosaurs carried their tails outstretched with horizontal backs. Students will cite the URL of the site in which they found their information. Next, students will assume the role of scientist. Using their newfound knowledge, they will propose a reason that they feel supports the argument about how dinosaurs carried their tails.

In the second part, students will use knowledge gained from their study of forces and weight distribution to compare a dinosaur of their choice to a bridge. Students will compare their model of a dinosaur with an outstretched tail and horizontal back to the bridge of their choice.

  1. Develop background information. Why do scientists believe that dinosaurs had erect tails and horizontal backs? Use the links given to support this claim.
  2. Determine the characteristics of cable-stayed and suspension bridges using the link given. Which do you think best represents the "structure" of a dinosaur--a cable- stayed bridge, a suspension bridge, or a combination of these two types? Support your arguments. Remember--you are trying to convince ME!
  3. This looks like a neat activity. Let me know what you think.

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Evidence for dinosaurs holding their tails erect and their backs horizontal
10 pts -- Three supporting reasons using only suggested links.
15 pts -- Four supporting reasons. Additional reason should be creative. Examples: You could compare dinosaur dimensions to those of a bridge in a scale drawing. You could compare estimates of weight distribution in the dinosaur and in the bridge.
20 pts -- Fulfill the requirements above and find a new link to support your argument (hyperlink must be given and its contents printed out and included).
Type of bridge represented by a dinosaur
10 pts -- length approximately half a paragraph; two supporting statements)
15 pts -- length approximately three quarters of a page; three supporting reasons
20 pts -- length approximately a page; more than three supporting reasons

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