Estimating Dinosaur Speed from Trackways: A Step-by-Step Guide

1 Estimating Dinosaur Speed from Trackways Testing the Method of R. McNeill Alexander (1989) Fossil footprints are of great interest to paleontologists because they record information about what an extinct animal was doing while it was alive and moving around. Careful analysis of fossil tracks has the potential to reveal several aspects of the behavior of the trackmaker, including posture, herding behavior, and walking or running speed. A basic fact of vertebrate motion is that the faster an animal is moving the farther apart its footprints fall along a trackway (Figure 1). By measuring the spacing of fossil footprints it is possible to estimate the speed of the trackmaker, but only after making several assumptions based on footprint size and the behavior of a wide range of living animals. A widely applied method for estimating speed from trackways was developed through the research of R. McNeill Alexander, an expert in biomechanics. This exercise is designed to lead you step-by-step through the methods and principles involved in estimating speed of movement from trackway data using Alexander’s method. We will apply it to measurements taken from a variety of dinosaur trackways. Establishing the Nature of Trackway Data Footprints / tracks: individual foot impressions. In a continuous line these form a trackway. Footprint size is also important because it can be used to estimate leg length, which is an important parameter for estimating speed. Estimating leg length from footprint size. How do we arrive at an estimate of how long an extinct animal’s leg was from the size of its footprint? We note a basic physiological fact - larger animals have larger feet. This makes sense because the larger you are the more you weigh and the larger your feet need to be to support that weight. The best way to test this idea is to measure foot size and leg length for a wide variety of individuals (and species) and examine the data to see if there is a simple relationship. For dinosaurs, Alexander (1989) notes that most dinosaurs have leg lengths that are about 4 x the length of the foot (based on his own copious measurements of a variety of dinosaur skeletons).

2 Establishing the relation between speed and stride length. Stride: The distance between footprints from the same leg / foot. Dynamic Similarity and Dimensionless Speed Alexander’s method is base d on the concept of dynamic similarity , which is the idea that structurally similar animals (for example, tetrapods) function equivalently according to the laws of physics. Put simply, the dynamic differences between a Chihuahua and an elephant when they are both walking come from their different sizes. If we can adjust for size, they will show the same dynamic behavior. How do we adjust for size? We need to calculate a quantity called dimensionless speed . This is speed that has been adjusted for the size of an organism based on its leg length and the force of gravity. Two animals moving at the same dimensionless speed will be dynamically similar. Alexander (1989) measured speed and stride length for a variety of living animals, including large and small mammals, ostriches, and humans. When he calculated relative stride (stride / leg length) and dimensionless speed, he discovered a consistent linear relationship between these two quantities (Figure 4). In other words, regardless of what kind of tetrapod you are, your stride is related to your speed in the same way once you make adjustments for your size. If we make the reasonable assumption that extinct tetrapods like dinosaurs functioned the same way as the great variety of living tetrapods, then we can apply this same relationship between stride and speed to dinosaurs. Measuring stride from a fossil trackway and estimating leg length from the size of the footprint, we can arrive at an estimate of speed for different types of dinosaurs.

3 Estimating Speed from Trackways – Steps to Calculate Measurements

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4 Part I - Estimating Dinosaur Speed from Trackways - Applying the Method Having demonstrated that Alexander’s method works, we can now apply it to actual fossil trackways to learn something about the behavior of dinosaurs. Figures 5 and 6 show five different dinosaur trackways made by different species of dinosaurs during different periods of the Mesozoic. For each trackway, use the scale bar provided to measure footprint length and stride length. Try to be as accurate as possible, measuring as many strides as possible for each trackway to obtain an average. Note that some trackways only permit measurement of a single stride. Trackway #5 (Figure 6) is shown in a photograph with a meter stick lying between tracks of the left and right foot. Estimate this distance (the pace) and then double it to estimate the stride. Recall that there are 100 centimeters in a meter and that a meter stick is divided into 10 cm segments (these are enhanced with black lines in the photograph). Because of the angle at which the photo was taken the apparent distances are somewhat distorted – for example, the footprint in the foreground is about 30 cm in length but looks larger relative to the measuring stick. Make your best estimate! 1. Complete the table below: Trackway Measured foot size Estimated leg length Measured stride length Relative stride length Estimated dimensionless speed Estimated speed MPH 1. Cret. Ornithopod x4 2. Jur. Sauropod x4 3. Trias Theropod x4 4. Trias Prosauropod x4 5. L. Cret. Theropod x4 Meters/sec x 2.24 = miles/hour (MPH) STEP 1 STEP 2 STEP 3 STEP 4 STEP 5

5 Figure 5 Dinosaur Trackways

6 Figure 6 Dinosaur Trackways

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7 Answer the following discussion questions from Part I: 2. Which dinosaurs appear to have been walking and which were running? What do the running dinosaurs have in common and why might they have been habitually moving faster than other dinosaurs? 3. What does it mean when the method for estimating speed from trackways yields a negative number? 4. Do these estimates probably represent the extremes of dinosaur speed? In other words, should we conclude from these trackways that most dinosaurs were incapable of running? Part 2 - Dinosaur Trackways at Dinosaur Valley State Park, TX The following dinosaur tracks are visible at Dinosaur Valley State Park, TX: Five main track site areas have been mapped within Dinosaur Valley State Park. Each of these areas has named individual track sites. These Tracks are Cretaceous in Age and estimated to be 115 million years old. Two types of tracks are visible at these sites: 1. Sauropod tracks, large elephant-like tracks believed to have been made by Sauroposeidon proteles (blue tracks)

8 2. Theropod tracks, smaller and often with a distinct three-toed pattern, believed to have been made by Acrocanthosaurus (red tracks). Some of the theropod tracks are classified as "elongated" because the dinosaur was walking on its metatarsal bones. Many of these tracks do not show the typical three- toe pattern because the tracks were made in runny, deep mud, and the toe impressions were buried. Assignment Directions • Use the following link to download Google Earth Pro to your desktop. https://www.google.com/earth/versions/ • Next, with GOOGLE Earth open, click the link for the kmz file for Dinosaur Valley State Park from Canvas, this will open the file in your temporary places in GOOGLE Earth • Click on the kmz file to open it in Google Earth. This will give you a file for the State Park in the Google Earth Temporary Places. • When you click on this file the following box will open: • Click on the link for Park Website. It will take you to Texas Parks and Wildlife. • Next, click on the Mapping Dinosaur Tracks tab near the top of the page below the name of the park. • There are several trackway overlays that you will need to click on and add to Temporary Places under the Park File. Do this by scrolling down, finding the file, and simply clicking on the following trackways files in their corresponding areas. • These are the trackways you will need to add: o Area 2 ▪ Main Site Tracks Overlay ▪ South Main Site Tracks Overlay ▪ Ozark Site Tracks Overlay ▪ South Ozark Site Tracks Overlay o Area 5 ▪ Lone Ranger Site Tracks Overlay ▪ West Taylor Site Tracks Overlay

9 • Right click on the kmz file and each trackway file and save them to “My Places” so your files will be saved if you have to exit Google Earth. • Using the measurement tool in Google Earth, take measurements of the following tracks at each site and complete the table below • Answer the discussion questions • Refer to figure 2 in the handout to help you obtain your measurements. 1. Complete the table below Estimating Dinosaur Speeds from Trackways at Dinosaur Valley State Park, TX Trackway Measured Foot size Estimated Leg length Measured Stride length Relative Stride length Estimated dimensionless speed Estimated speed MPH Main Site Tracks – Sauropod South Main Site Tracks - Theropod South Ozark Tracks - Sauropod South Ozark Tracks - Theropod Lone Ranger Site – Theropod West Taylor Site – Theropod Leg length = 4x foot size Discussion Questions – Part II 2. Look at the Theropod tracks to the left of the trackway in South Main Site. What are the possible reasons these tracks are side-by-side? 3. At the Ozark Site what differences do you find in the sizes and strides of the theropod tracks? Were they walking, running, adults, juveniles? Assuming these tracks were made at the same time, what could this mean? What about the sauropod tracks at the same site?

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10 4. Compare the size of the sauropods to the theropods in South Ozark Site based upon the track width x 4 = leg length. Which ones were likely to be adults? 5. The Lone Ranger Site Trackway is the longest trackway in the park. Use the measurement tool in Google Earth to determine how long the trackway was. How big was the theropod that made this trackway? Did they appear to be running or walking? 6. The West Taylor site tracks have a very different appearance from the Lone Ranger Tracks. What are the differences that you see in the tracks at West Taylor? How many different animals do you think made these tracks? What type of sediment were they likely walking in? Knowing that theropods were not swimming dinosaurs, what could this indicate about the environment that they were walking in at the time? What to Turn In: This worksheet, Including completed tables of measurements and calculations from the worksheet and from Google Earth, answers to all discussion questions References Alexander, R. McNeill, 1976, Estimates of speeds and dinosaurs. Nature 261:129-130. Alexander, R. McNeill, 1989, Dynamics of Dinosaurs and Other Extinct Giants, Columbia University Press. Kuban, G. K., 2004, An Overview of Dinosaur Tracking [online]. Available: http://paleo.cc/paluxy/ovrdino.htm [6-08-2005]. Lockley, M. and Hunt, A.P., 1995, Dinosaur Tracks and Other Fossil Footprints of the Western United States, Columbia University Press, 338 p.

Module 13 Investigation-2

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