LAB 7

Dinosaur Trackways Exercise

Introduction

One of the goals of paleontology is to reconstruct the biology, including behavior, of extinct organisms. But because they no longer exist, we are not able to directly observe their behavior. Paleontologists must use evidence that allows them to indirectly “observe” the behavior of extinct organisms.

Trace fossils, the records of the activity of fossil organisms, provide important information about fossil behavior. Fossil footprints and trackways, important types of trace fossils, are known in the fossil record. Fossil trackways can provide information that is not possible to obtain with fossil hard parts alone. Unlike the bones, trackways are a record of the dynamics and behavior of animals (see Figure 13.2).

In the past few decades, ideas about how dinosaurs lived have changed dramatically. Dinosaurs are no longer perceived as slow, lethargic reptiles, but as active, even sprightly animals—in no way inferior to the mammals that eventually replaced them.

Some of the most important evidence for this new view of dinosaurs comes from analyses of dinosaur trackways. This evidence suggests that dinosaurs were much faster and athletic than once believed, and were able to sustain high levels of activity.

So, how fast were dinosaurs? You will use some simulated trackways and the mathematical methods of Alexander (1976) to obtain estimates of speed in two species of dinosaurs.

Estimating dinosaur speed

Two simulated trackways are painted on the sidewalk. One is of the theropod Tyrannosaurus, the other is of the ceratopsian Triceratops. You will take simple measurements from these trackways. Remember, we can never truly be sure how fast a dinosaur could run, since we don’t know if a particular trackway was made by the animal at its maximum running speed.

Step one. The first measurement you need to take is the stride length of each species. Stride length is the distance (in meters) between two successive prints made by the same foot (right to right, left to left). For each of the trackways, determine if the dinosaurs speed is constant—that is, does the stride length change within the trackways. A faster moving animal has a longer stride. If the speed (i.e., the stride length) does change, take a measurement at the longest stride (fast) and another at the shortest stride (slow). For each of the trackways, measure the average stride length and record values in Row #1 of the data sheet.

Step two. Now, calculate the relative stride length for each dinosaur. Relative stride length equals the measured stride length divided by the leg length. Leg length ( the distance from the ground to the hip joint) can be approximated as five times the foot length. Enter the measured foot lengths and leg lengths in Rows #2 and #3, respectively. Then record the calculated relative stride lengths in Row #4 of the data sheet.

Relative stride length essentially normalizes for variation in leg length. A taller dinosaur will have a longer stride length than a shorter one, even if it is moving at the same speed.

Step three. Use your values of relative stride length and Figure 13.7 (graph of dimensionless speed vs. relative stride length) to determine the dimensionless speed of each dinosaur. The dimensionless speed is a value that accounts for variation in overall body size. All other things being equal, a bigger animal moves faster than a smaller one. But the running movements of two different animals can be made similar if the skeletal length, tempos, and forces are properly adjusted, or normalized. Record the dimensionless speeds in Row #5.

Step four. An estimate of actual speed can be obtained with the following equation:

Speed = (dimensionless speed) x Ö (leg length) x (gravitational acceleration)

Gravitational acceleration = 9.8 m/sec²

Enter the calculated speeds of the dinosaurs in Row #6.

Step five. Convert the speed from metric units of m/sec to the more familiar (to Americans, anyway) English units, using the conversion

1 m/sec=2.24mph

Enter the converted speeds of the dinosaurs in Row #7.

For further reading:

Chapter 13 in your textbook

Alexander, R.M., 1976. Estimates of speeds of dinosaurs. Nature 261: 129-130

Alexander, R.M., 1989. Dynamics of Dinosaurs and Other Extinct Giants. Columbia Univ. Press. New York, 167p.

Alexander, R.M., 1991. How dinosaurs ran. Scientific American. April, 1991, p. 130-136.

Lockley, M., 1991. Tracking Dinosaurs: A New Look at an Ancient World. Cambridge Univ. Press, 28p

	Triceratops	Tyrannosaurus (slow)	Tyrannosaurus (fast)
1. Stride length
2. Foot length
3. Leg length
4. Relative Stride Length
5. Dimensionless speed
6. Speed (m/sec)
7. Speed (mph)

QUESTIONS

1. Sketch the foot print made by the tyrannosaur and both the foreprint and the hindprint of the ceratopsian.

2. Describe the walking posture of these animals. Were they upright or sprawling? You can answer this by noting if the limbs were held out to the sides or if the limbs were mostly beneath the body (see Appendix for diagram)

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3: Describe how the quadruped Triceratops moved. Note that the foreprints are very close to the hindprints. How did this happen? Do both forelimbs move, followed by both hindlimbs? Do both right limbs move, then both left? Is there an alternation of limb movement: right front, then left rear, then left front, then left rear?

4. Briefly describe one assumption made in your estimates of dinosaur speed that could be responsible for either over-estimating or under-estimating the speed.

5. A world record time for humans over 100 meters is about 1m/sec. Average speeds for this distance are closer to 7 m/sec, or 15.7 mph. Could you outrun these dinosaurs over that distance?

APPENDIX

A. The sprawling posture of primitive amphibians and reptiles; B. The semi-upright posture of crocodiles and advanced mammal-like reptiles; C. The upright posture of a dinosaur