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.
Grade Span: 68 or 912
Note:all images in packets courtesy of Brent Beithaupt, The Geological Museum, University of Wyoming
Make student packets (see materials).
Prepare overheads (see materials).
Time: Two to three class periods
Grouping: Groups of 3 or 4 and whole class
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.
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.). DinosaursThe Science behind the Stories. American Geological Institute. Pp. 117126.
Explore these links for additional information on the topics covered in this lesson:
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: www.ucmp.berkeley.edu/fosrec/Heindel3.html.
Vocabulary: trace fossils, tracks, trackways, stride length, hip height, relative speed, bipedal, quadrupedal, ripple marks
Guide students as needed, but eventually students should:
Study the tracks and determine that the tracks were made by a bipedal animal.
Describe the trackmakerthree-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.
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!
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