Dinosaur Speed Trap

This EarthCache will take you to the Picketwire Canyonlands Dinosaur Tracksite. Withers Canyon is the only allowable access to the canyonlands for the general public. Parking can be found near N 37 39.584, W 103 34.251. Hiking, non-motorized bicycles, and horseback are the only allowable access. It is a minimum 11 mile round-trip from the parking area to the tracksite and back, with 500 feet of steep elevation change at the beginning and end of the hike. Once you reach the tracksite, you will need to cross the Purgatoire River, which may be ankle-deep to waist-deep. Know your limits and plan your hike carefully as there is no overnight camping in the Picketwire Canyonlands. There is no drinking water available in the canyonlands, and at least one gallon of water per person should be taken with you. There is very little shade, so be prepared for the heat.

Picketwire Canyonlands is home to several rock art sites, as well as the Delores Mission and Cemetery. Please remember that cultural and paleontological resources on public lands are protected by law. Do not damage or remove cultural or paleontological resources. Making casts of the dinosaur tracks is not permitted without permission of the Comanche National Grasslands, U.S. Forest Service.

The Picktewire Canyonlands Dinosaur Tracksite is the largest dinosaur tracksite in North America. It is about one-quarter mile long, contains over 1300 visible tracks which make up over 100 distinct trackways, and is located on both sides of the Purgatoire River in rocks of the Morrison Formation. The Morrison Formation, laid down approximately 150 million years ago during the Jurassic Period, is well known for producing fossilized remains of dinosaurs and other animals. There are also at least 30 known dinosaur trackways preserved in Morrison Formation strata.

The rock layers in this formation aid in understanding the local conditions from when the tracks were made. Research of this site indicates that the tracks were made along a shallow shoreline near the edge of a freshwater lake. Remains of dinosaur fossils from sauropods (brontosaurs) have been found at the tracksite and nearby on private land. Other fossils found at the site include the remains of plants, fish, and invertebrates such as crustaceans, clams, and snails. Trampled plant stems are present, as are the remains of at least two dozen clams which were trampled and killed by sauropods.

Lockley et al. (2000) states, “Tracks are the evidence of living animals and provide biological insights into the trackmaker’s anatomy and behavior.” Tracks can tell how large an animal was, how many feet it walked on (two or four), and how many toes it had. Along with the age of the rock, this can help to identify the type of animal that made the tracks. Additional information gained from tracks at the Purgatoire Tracksite include social behavior (sauropods at this site can be seen to have moved in groups, whereas theropods such as Allosaurus moved as individuals) and the speed at which the dinosaurs moved when making the tracks.

The aim of this EarthCache will be to calculate the approximate speed that a dinosaur was moving when it made a particular set of tracks. To complete this task, you will need to: 1.) Determine that a set of tracks were made by a theropod (Allosaurus) or sauropod (brontosaur); 2.) Measure track length and stride length; and, 3.) Plug the lengths into a formula which will give you an approximate value for speed.

The first thing to do will be to determine the type of dinosaur that made a particular track. Two broad types of tracks were made at the Picketwire Tracksite: large quadruped tracks made by sauropods (brontosaurs), and three-toed tracks which were made by bipedal dinosaurs.

Brontosaur tracks at the Tracksite tend to be round in shape with no toes visible, or short stubby toes at the front of the tracks. Non brontosaur tracks at the tracksite were made by bipedal animals with three-toed footprints. These tracks often have thin indentations at the ends of the toes that were formed from claws. According to Lockley et al. (2000), “most if not all, of the three-toed tracks from the Purgatoire Tracksite were made by theropods.” Several series of good identifiable sauropod tracks are found directly to the west of the given coordinates. Theropod tracks can be found at the coordinates and on the north side of the river.

To calculate the speed of a dinosaur using a trackway, measure the footprint length (straight line distance between the tip of the longest toe to the back of the foot) and stride length (distance between two successive placements of the same foot measuring between equal points). Multiply the footprint length by four to get an estimate of the hip height. Use these measurements in the following formula:

v=0.25 (g^0.5) x (sl^1.67) x (h^-1.17)

Where v=velocity or speed, g=the acceleration due to gravity (9.8 m/sec^2), sl=stride length, and h=estimated hip height (or 4 times the footprint length). It is important that your measurements are in meters taken to at least 2 decimal places.

Your answer to this formula will be in meters/second. Your final mathematical problem will be to change your answer to miles/hour. Since it is easy enough to find estimates of dinosaur speed on the internet, you will need to show me your work in the email that you send.

So, to log this EarthCache here are the things you will need to send me in an email: 1.) The type of dinosaur track (theropod or sauropod) from which you made your measurements; 2.) The footprint length and stride length; and 3.) Your final speed in meters/second and miles/hour. Remember that you must include all work in your email!

Please consider posting photos of yourself, or the local geology, when you log this EarthCache. Photos can be an additional rewarding part of your journey, but posting them is not a requirement for logging this EarthCache, and is strictly optional.

The above information was compiled from the following sources:

Pike & San Isabel National Forests, Cimarron & Comanche National Grasslands Website: Picketwire Canyonlands Dinosaur Tracksite http://www.fs.fed.us/r2/psicc/coma/palo/index.shtml and Comanche National Grassland – Picket Wire Canyon http://www.fs.fed.us/r2/psicc/coma/main/picketwireguide.shtml

Santa Fe Trail Scenic and Historic Byway, The Mountain Branch. Website: Picket Wire Canyon on Comanche National Grasslands http://www.santafetrailscenicandhistoricbyway.org/pwdino.html

1976. Alexander, R.M. Estimates of Speeds of Dinosaurs. Nature. Vol. 261.

2006. Alexander, R.M. Dinosaur Biomechanics. Proceedings of the Royal Society: Biological Sciences. Vol. 273. Online at http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1634776

2007. American Museum of Natural History. Activity: Relative Speed of Dinosaurs. Online at: http://www.ed.mtu.edu/pd/documents/McGinnis_DinosaurFootprintActivity.pdf

2000. Lockley, M.G. et. al. A Guide to the Purgatoire Dinosaur Trackway, Excerpts from the Book Dinosaur Lake, Special Publication 40, Colorado Geological Survey, 1997; in Field Trip Guidebook A Dash with the Dinosaurs: A Mountain Bike Trek to the Purgatoire River Dinosaur Trackway and the Cretaceous-Tertiary Boundary Impact Layer of Southeastern Colorado, La Junta and Trinidad, Colorado.

University of California, Berkeley. Inferring the Possible Speeds of Dinosaurs. Online at: http://www.ucmp.berkeley.edu/diapsids/buzz/locomotion.html

Thanks to the Comanche National Grassland for allowing placement of this EarthCache!