Interpreting the Tracks Authors: Brent Breithaupt and Judy Scotchmoor

Overview: Students will discover the relationships among foot length, leg length, stride length and speed in bipedal animals. Data collected and graphed for a student population will be applied to track data from a research site in Wyoming to make inferences about dinosaur physiology and behavior. Trackways provide direct data in the form of foot length/size and stride length. These data can provide clues about dinosaur speed.

Lesson Concepts:

• Life forms of the past were in some ways very different from living forms of today, but in other ways very similar.
• Most species that once lived on Earth have gone extinct.
• Fossils provide evidence of past life.
• Fossils provide concrete evidence of past life, including sequences of fossils showing gradual change over time.
• Form is linked to function.
• Physical, chemical and geological lines of evidence are used to establish the age of fossils.
• Scientists pose, test, and revise hypotheses based on research outcomes.
• Science explains the natural world using evidence from the natural world.
• We can learn about the natural world using our senses and extensions of our senses.
• Scientific ideas are developed through reasoning.
• Science does not prove or conclude; science is always a work in progress.
• Scientists use multiple lines of evidence to study life over time.

Grade Span: 6–8 or 9–12

Materials:

• Cm ruler and meter stick for each group of students
• Graph paper
• Calculators
• Student packet—one per group, containing copies of the following:
  — Theropod track and reconstruction [PDF version]
  — Aerial view of trackway and reconstruction of a single series of tracks [PDF version]
  — Reconstruction of complete track site [PDF version]
  — Geologic time scale and strata of the Mesozoic [PDF version]
• Overheads of:
  — All student materials as needed
  — Reconstruction of theropod traversing ripple marks [PDF version]
  — Main groups of dinosaurs and their tracks [PDF version]

Note:all images in packets courtesy of Brent Beithaupt, The Geological Museum, University of Wyoming

Advance Preparation:

— Make student packets (see materials).
— Prepare overheads (see materials).

Time: Two to three class periods

Grouping: Groups of 3 or 4 and whole class

Teacher Background:

As trace fossils, tracks and trackways represent preserved activities of animals in the past. Trackways provide direct data in the form of foot length/size and stride length. These data can provide information about the animals’ physiology, speed, and behavior. However, interpretation of the data is dependent on several factors, including whether the animal was bipedal or quadrupedal, the size and weight of the animal, how the foot was placed, how the animal stood, the number of digits, the surface on which the animal was moving, and the preservation of the tracks.

By studying the tracks and trackways made by living animals, scientists have found sufficient consistency in the data to provide accurate correlations between the trackway data and the size and speed of the trackmaker. These same correlations can be applied to the tracks and trackways of extinct animals, such as dinosaurs.

The basic measurement of a dinosaur footprint is its length, represented as FL. The ratio of footprint length and hip height (h) is different for different groups of dinosaurs, but generally the hip height of a bipedal dinosaur is roughly four times the footprint length. The speed can then be determined as relative speed, which is stride length (SL), divided by hip height (h). Generally speaking, if the SL/h < 2.0, then the animal was walking; > 2.9, the animal was running; and between 2.0 and 2.9, the animal was trotting.¹

The particular tracks and trackways used for this activity are several of thousands found in the Lower Sundance formation of the Middle Jurassic in Wyoming. The presence of ripple marks on the trackway surface, coupled with trace fossils of burrows of marine animals, have led to the interpretation that many individual theropod dinosaurs of different sizes and ages were walking together across ancient tidal flats. Thus trackways can provide information about who was there, what they looked like, what they were doing, how they were interacting, and what the paleoenvironment was like.

Teacher Resources:
¹ Wright, J.L., and B.H. Breithaupt. 2002. Walking in their footsteps and what they left us: dinosaur tracks and traces. In J. Scotchmoor, D.A. Springer, B.H. Breithaupt, and A.R. Fiorillo (eds.). Dinosaurs—The Science behind the Stories. American Geological Institute. Pp. 117–126.

Explore these links for additional information on the topics covered in this lesson:

• Fossils
• Nature of Science
• History of Life

Teaching Tips:

You may want to precede this activity with an introduction into interpreting tracks and trackways in order to differentiate between observation and inference. There are several such tracks available such as those at: ucmp.berkeley.edu/fosrec/Heindel3.html.

Vocabulary: trace fossils, tracks, trackways, stride length, hip height, relative speed, bipedal, quadrupedal, ripple marks

Procedure:

Part I: Finding Correlations
1. Class discussion: Think/Pair/Share—Ask students to think and write about what tracks and trackways can tell us.
2. The discussion may include questions such as these:
      — Where were the tracks found? This might provide clues as to the trackmaker, i.e., three-toed tracks found in rocks of the Pliocene could not be dinosaurs!
      — Who was there? What are the clues that help you determine the trackmaker?
      — How fast were they moving? What are the factors involved in speed? If you only have a series of footprints, how can you determine speed? [Hint: If a dozen of you lined up outside, somewhere safe and flat, and you each took 100 steps, would you all cover the same distance? Why not? Leg length and stride are important. But without the leg and only the track, how can we figure out the leg length? Is there a relationship between foot length and leg length?
3. Have students remove their shoes and measure their feet in cm. Using a tape measure or meter stick, have students measure the distance from their hips to the floor in cm. (Working in pairs is helpful. Hip height should be measured to the point at which the ilium protrudes.) Have each student determine the foot length (FL) to hip height (h) ratio.
   Gather all class data.
   On average, the FL:h = ~1:4 and this is generally true of all bipedal animals.
4. If time, weather, and facilities allow, have students discover the correlation between stride length and hip height as a determinant of relative speed. This can be done by having each student walk across a surface of sand and measure his or her stride length. Then have students repeat the activity while running. [NOTE: make sure that students measure a stride length from either a left to left print or a right to right print. A single step is considered a pace, not a stride.] If students divide their stride lengths by their hip heights, they will get a relative speed ratio. By gathering the class data, it will be clear that the SL/h while walking will be much less than while running. If there is not time for this activity, lead a discussion about the activity and inform students that scientists have run similar experiments on numerous bipedal animals with the following results: Generally speaking, if the SL/h <2.0, then the animal was walking; >2.9, the animal was running; and between 2.0 and 2.9, the animal was trotting.
5. Class discussion: How can we apply this information to tracks and trackways of animals in the past? What kinds of hypotheses can we make?

Part II. Applying the data:
6. Hand out the student packet and allow sufficient time for students to interpret the data. Let them know that they will be presenting their hypotheses and the evidence supporting their ideas to the rest of the class.

   Guide students as needed, but eventually students should:
      — Study the tracks and determine that the tracks were made by a bipedal animal.
      — Describe the trackmaker—three-toed, bipedal animal.
      — Notice that the tracks were found in rocks from the Middle Jurassic.
      — Perhaps infer that the track was therefore made by a theropod (carnivorous dinosaur).
      — Measure the length of the single footprint (FL) and multiply by four to determine hip height(h).
      — Determine the relative speed by dividing the stride length (SL) by the hip height (h).
      — Notice that there are numerous tracks of different sized individuals all traveling together, probably walking.

7. Have student groups present their findings and hypotheses to the rest of the class.
   Discuss and compare.
8. Ask students what other information might be available from the site.
9. Show the overhead of the theropod walking across the ripple marks. Ask students to comment on the reconstruction. There is another piece of information visible - the substrate on which we find the tracks. In this particular case we see ripple marks on the trackway surface. These coupled with trace fossils of burrows of marine animals have led to the interpretation that the dinosaurs were walking together across ancient tidal flats.
10. Class discussion to summarize how scientists use multiple lines of evidence to interpret the past.

Extensions:

Form and function are closely related. Collect pictures of the skeletons of several mammals. Have students place them into groups according to how fast the animals can run. Then closely examine the limb types and foot postures of the mammals. Introduce the terms:

   — Plantigrade: walking with the sole of the foot on the ground, such as in humans or bears.
   — Digitigrade: walking with the heel and ankle raised off the ground; the weight of the body is born by the digits only, such as in an ostrich or cat.
   — Unguligrade: walking on the toe tips, such as in a horse or deer.

Have students compare the length of the upper leg (femur) with the length of the lower leg (tibia/fibula in the plantigrade; tibia/fibula and metatarsals in the digitigrade; and tibia/fibula, metatarsals, and phalanges in the unguligrade). As T. rex has an upper to lower leg ratio rather similar to our own, this can lead to an interesting discussion on just how fast T. rex was capable of running!