OBJECT OF THE MONTH - APRIL 2007
Theropod Track
Theropod track from the Cretaceous Dakota Formation. UCM 89113.
A footprint or track is formed by the interaction of an animal's foot with a soft substrate, and is preserved by rapid infilling with mud or sand. A sequence of footprints is called a trackway, and provides scientists with important information concerning the posture, gait, foot structure, speed, and social behavior of an animal.
Footprints, bite marks, claw marks, burrows, borings, nests, coprolites, and feeding traces and all example of trace fossils. Trace fossils such as footprints are the closest scientists can get to studying extinct animals as moving, dynamic animals.
Trackways have helped paleontologist determine that dinosaurs had an upright (not sprawled) posture, held their tails off the ground (there are very few tail tracks compared to footprints), moved in herds, and used migration corridors. Additionally, trackways are often the only evidence paleontologists have recording the presence of extinct animals in a specific region. The size and shape of the footprint can help identify the type of animal that made the track.
The track pictured here is a theropod footprint from the Late Cretaceous Dakota Formation. The Dakota Formation preserves shoreline sediments deposited ~100 million years ago along the Western Interior Seaway which covered central North American from the Gulf of Mexico to the Arctic Ocean. Conglomerates, sandstone, and shales represent fluvial (river), beach, and marine deposits. Although body fossils are generally rare from the unit, numerous bird, theropod dinosaur, and ornithopod dinosaur tracksites have been described, permitting paleontologist to better reconstruct the paleoecology of the region. Theropod tracks are distinguishable by their tridactyl (three-toed) prints with narrow toes and no "heel" impression.
Dinosaur footprints have been found at several sites across Colorado. Dinosaur Ridge near Denver, Colorado, is the location of trackways preserved in Jurassic Morrison Formation sediments and Cretaceous Dakota Formation sediments. Picketwire Canyonlands near La Junta, Colorado, is the location of trackways in the Jurassic Morrison Formation.
For more information on dinosaur tracks:
- M. Lockley and A.P. Hunt. 1995. Dinosaur tracks and other fossil footprints of the western United States. Columbia University Press, New York.
- M. Lockley. 1991. Tracking dinosaurs: a new look at an ancient world. Cambridge University Press, New York.
- T. Thulborn. 1990. Dinosaur tracks. Chapman and Hall, New York.
- D.D. Gillette and M.G. Lockley. 1989. Dinosaur tracks and traces. Cambridge University Press, New York.
