Purpose: To understand how scientists can make inferences and construct explanations about animal movement by analyzing those animals’ tracks.

Procedural overview: Just as the scientists in “Robot re-creates a tetrapod’s moves” analyzed tracks and other data to make inferences about an ancient tetrapod’s gait, students will analyze tracks created by classmates. After pairs of students make sets of tracks using varied gaits of their choice, they will trade with each other and study unfamiliar tracks. By using what they know about human range of motion, gravity, friction and balance, students will try to infer how their classmates made the unfamiliar tracks and what style of gait was used.

Approximate class time: One class period.

Supplies:

Activity Guide for Students: Tracing Tracks and Guessing Gaits

Lots of newspapers, newsprint or packing paper

Clear packing tape

Plastic bowls of water

Paper towels

Pencils

Tape measures

Cell phone timers or stopwatches

Calculators

Rubber bands

Optional: Classroom computer projector to show video clip

Directions for teachers:

Have students work in pairs to make tracks on paper according to the directions for students below, ideally in locations where other students can’t watch (in different hallways at school or even at home). On a separate sheet of paper, students should write down their names and information about their tracks.

Then collect the paper trackways and student information sheet, mark each pair’s trackways and student information sheet with the same letter and redistribute the trackways so each pair has a new set.

Pairs should use the Activity Guide for Students to analyze the trackways to see how much can be learned about other students’ gaits. Be sure to provide more newspaper so students can test their hypotheses. You can choose to share the student information sheet with the pairs only after they have analyzed the trackways and tested their hypotheses.

Notes to teachers:

If time permits, before students begin, consider playing the video of the tetrapod robot from the article “Robot re-creates a tetrapod’s moves.” Remind your students that the more irregular their walks, the harder it will be for other students to analyze the gait.

Instead of using paper, students could make and study footprints in sand or soft soil outside. That approach would permit measurements of the depth of the tracks and estimates of speed based on depth and depth variations in tracks.

Students could also, or alternatively, build and then analyze the gaits of different types of walking robots. That activity ties in well with the robotic reconstruction described in the Science News article. Good sources for a variety of simple, inexpensive robot kits include American Science & Surplus, Home Science Tools, Educational Innovations Inc., and Scientifics Direct.

Directions for students:

As discussed in “Robot re-creates a tetrapod’s moves,” researchers tried to reconstruct the gait of Orobates pabsti, a creature that lived between 280 million and 290 million years ago, based on its fossilized skeleton and tracks. Inferences about a wide variety of prehistoric creatures, from worms to dinosaurs to hominids, have been made based on the tracks these animals left behind. And studying the tracks and gaits of living creatures can help us better understand everything from the population sizes and ranges of endangered animals to how to design prosthetic limbs to reconstructing crime scenes.

In the first part of this activity, you will work in pairs to make tracks on paper. Follow your teacher’s instructions to find a place where other students from the class can’t observe you.

In the second part of the activity, you will trade trackways with another pair of students. You and your partner will use what you know about human range of motion, gravity, friction and balance to analyze the trackways and try to infer how your classmates made the unfamiliar tracks and what style of gait was used.

Making tracks

1. Spread out newspaper sheets and tape them together securely to make a paper path at least 3 meters long (about 10 feet). Then flip the path over, so the tape is on the bottom, where it won’t interfere with making and measuring tracks.

2. Choose a gait to use to go down the paper path. You can choose to travel either forward or backward; to walk, run, hop, skip, etc.; to walk with your feet, with your knees, on all fours, crawling like a crab, etc.; to use different shoes, socks or go barefoot. Your gait should have the same approximate speed and method for the entire path — no speeding up or slowing down, no changing style along the way. Your partner can choose the same gait as you or a unique gait.

3. Once you have decided on your gaits, use a bowl of water or wet paper towels to wet your feet and any other parts of you that will come in contact with the paper. You want to leave good prints.

4. Now make your prints. Go down the same paper path, one at a time, to make the prints. It’s OK for you and your partner’s trackways to overlap, but try to avoid too many cases where individual prints overlap since that will make measuring the tracks difficult.

5. Have your partner time how long it takes you to get to one end of the paper to the other.

6. Immediately after making wet tracks, trace around each track with pencil or marker to outline the tracks before the water dries.

7. Write down information about your tracks on a separate sheet of paper:

Student 1 time:

Student 1 gait (describe in as much detail as possible):

Student 2 time:

Student 2 gait (describe in as much detail as possible):

8. When you are done creating your paper trackways, roll up your paper (adding additional tape for support if necessary) and put rubber bands around it. Do not write your names or other information on your paper trackways.

9. Give the paper trackways and the student information sheet to your teacher.

Studying tracks

1. Obtain from your teacher paper trackways that were made by another pair of students.

2. Can you determine two distinct sets of tracks even if the tracks overlap? How did you figure it out?

3. Use a tape measure to find the following information about one set of tracks and record your results.

Length and width of each type or shape of print (make a note if you can distinguish footprints from handprints).

Average length and width for each type of print (if they vary in size).

Student 1 length (along the trackway) from one track until that same sort of track is repeated (how far the student traveled while going through one complete cycle of motion for that gait). If there are several cycles of a given type along the trackway, measure and record them all, then calculate the average.

Are there any other quantitative measurements you could take? If so, take those measurements and record them below.

4. What type of information might be inferred about the physical dimensions of the human from the quantitative track data collected?

Leg length or overall height could be guessed, but the guess would not be conclusive.

5. What qualitative observations can you make about the tracks? Record any observations that could be helpful in determining the gait used. Consider, for example, the shape of the prints and track and how uniform the track looks across its length.

Analyzing the shape of the print should be helpful. Is it a hand, foot or something else? Is it a full print or partial print? Uniformity of the track could provide clues to whether the gait is well-balanced.

6. Based on the quantitative and qualitative track data you collected, predict the style of gait you think the student used.

Student answers will vary, but students should generate a hypothesis based on their observations.

7. At what speed do you think the student traveled down the path? Do a quick test using a measuring tape and a timer if you need a rate to use as a reference.

A typical walking speed might be about 1.5 meters per second. If tracks look like a full shape of a shoe, this could indicate a normal to slow walking speed. If partial shoe tracks are noted, then the student may have jogged or ran.

8. Test your gait hypothesis by trying to reproduce similar tracks with your own motions. If your first hypothesized gait cannot generate a similar track, generate and test other hypotheses. Describe the gaits you try and which one best matches the track pattern. Can you reproduce the exact gait? Why or why not?

Student answers will vary. A different student will not be able to produce the exact trackway due to differences in body size.

9. Repeat steps 3 through 7 for the second set of tracks.

10. Obtain the written descriptions for how the other students actually made the tracks. How well did you do at figuring it out? What were the easiest aspects to figure out, and what were the hardest aspects?

Student answers will vary.

11. How close were you on your speed estimates? Would knowing the speed have helped you figure out the gait?

Student responses on the accuracy of speed estimates will vary. Speed of movement will depend on a person’s body dimensions and how fast they choose to move with a particular gait, so it will not definitively indicate gait. However some gaits require more time to complete than others, so knowing speed might help narrow down the type of possible gait.

12. Think about the qualitative and quantitative track data that you collected. Predict how each of the following factors could change the tracks from each student’s gait.

An increased range of motion of the ankle joint in humans.

Tracks might be farther apart.

A decrease in the gravitational force on Earth.

Tracks might be farther apart and tracks might not be full impressions of the body part used to make them.

An increase in the frictional force between the surface and the body part in contact with the surface.

Tracks might be closer together.

13. What have you learned about methods of analyzing tracks?

There are many qualitative and quantitative measurements that can be made on an animal trackway, but knowledge about the animal’s body shape, size, skeletal and muscular structure, joint mobility, etc., is also very helpful when trying to infer an animal’s movement from its trackway. Animals of the same species can also have a variety of tracks.

14. What have you learned about the scientific method in general?

While analyzing the trackways, we used the scientific method to problem solve. We were presented with an unknown trackway that we had to analyze to come up with a hypothesis about a gait that could create the given trackway. Once we came up with our possible gait hypothesis for each trackway, we tested it by performing the gait and trying to reproduce the track pattern. If we could reproduce a similar gait, we knew that the gait could have been one that created the pathway. Thorough data collection, analysis and problem solving is essentially the scientific method.