Brooklyn College
City University of New York
Lab #6, ASSIGNMENT 3#Page 2

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POSTURE INDEX: We can solve this problem of whether bipedal dinosaurs had a sprawling or erect posture by finding the value of a parameter which we can call an animal's "posture index". The plan would be to calculate the posture index of a dilophosaur using the trackway painted on the floor of the corridor adjacent to Rm 4152, and to use the result to assess the stance of this dinosaur. The whole operation depends on the fact that tetrapod sprawlers have much more widely spaced feet than tetrapods with an erect posture (refer to the sketch on the previous page if necessary).

We will define posture index as:

         Posture Index = (leg spacing)/(foot length)

where leg spacing is the distance between the rear feet measured across the body; and foot length is the toe to heel length of a rear foot. The sketch below shows how to make these measurements.

To reach our goal, we need to calculate posture index for the corridor dilophosaur, and for a modern sprawling and erect tetrapod. We need posture indices for the modern animals to provide a framework in which to evaluate dinosaur posture indices. The idea is to compare the dilophosaur posture index value to values for modern tetrapods in order to see whether the dilophosaur figure falls closer to that for a sprawler or to that for an erect animal.

We will do this on page 3, starting with a modern sprawler.