Coal mining in the area has revealed thousands of footprints, and at each of the more than 20 tracksites identified to date, all of them show tracks of Ankylosaurs, a heavily armored, plant-eating, tank-sized, four-footed dinosaur that had stocky legs and a short, heavy body.
"There are only a couple of sites where there is a real diversity of tracks," said McCrea. In the few places where other dinosaurs existed, he found traces of small, medium, and large-size, meat-eating, two-footed theropod dinosaurs, and also those of birds.
What McCrea wanted to know was why the Ankylosaurs were everywhere but the bipedal dinosaurs were found only in certain places. An analysis of the tracksites revealed that the places with only Ankylosaurs were muddy bogs 70 million years ago.
"Why were Ankylosaurs in those areas," he asked. "Ankylosaurs are plant eaters. So where do you find plants? You find plants in low-lying well-watered areas."
By examining the footprints left by the Ankylosaurs, McCrea learned that their feet were wide and splayed out, a design that kept the dinosaurs from sinking in the mud like a snowshoe keeps a human from sinking in snow.
The bipedal tracks all show narrow digits, a foot design that would make walking in the mud quite difficult. All of the bipedal tracks are found in sediments that resemble firm ground such as sand bars, said McCrea. He said that understanding the difference between these tracksites "doesn't make sense until you look closely at the type of environment these animals were walking on and get an idea what they are doing or why."
When scientists hunt for dinosaur tracks they look for areas where ancient layers of sedimentary rock are exposed, such as cliffs, sea coasts, quarries, open-pit mines, desert arroyos, and along the banks of rivers and streams.
"The best tracksites are often those where well-preserved tracks occur in a rock that is very hard and resistant to erosion," said Lockley. "For example, with a tough internal cement in some sandstones. The worst tracksites are in very soft rock that is easily destroyed after coming to the surface."
Usually, tracks are not found in the same location as bones. This is mostly because the conditions that are ideal for preserving tracks, such as acidic sediments, are not very good for the fossilization of bone.
"It doesn't mean the bones weren't there, but after 70 million years the bones would dissolve whereas the tracks wouldn't," said Martin.
The separation of the tracks from the bones makes it difficult for paleontologists to match tracks and bones, but Lockley expects this ability to improve as the database of both tracks and bones increases in the years to come, commanding greater respect for the study of tracks among paleontologists.
"We have already passed the point where tracks are widely accepted as serious science," he said. "We can look forward to the discovery of tracks of more groups of extinct animals that until now have remained mostly undiscovered."
More National Geographic News Stories on Dinosaurs:
Four-Winged Dinosaurs found in China, Experts Announce
Utah Dinos May Have Been Killed By Drought
Cuban Dinosaur: First Confirmed Remains Discovered
Dinosaur Cannibal?Mystery in New Mexico
Tetrapod Fossil FoundFirst Ever in Asia
New Picture of Dinosaurs Emerging
Fossil Implies Our Early Kin Lived in Trees, Study Says
Weird Buck-Toothed Dinosaur Found
Dinosaur Tracks Preserved on Scottish Island
Dinosaur Tracks Shed Light on Sauropod Evolution
Comets May Have Led to Birth and Death of Dinosaur Era
Fossil of Dog-Size Horned Dinosaur Unearthed in China
Tyrannosaurus rex Was a Slowpoke
Researchers Rethink Dinosaur Die Off Scenario
Researchers Melt Polar Dinosaur Mysteries
Scientist's Finds Spur New Thinking on Dino Evolution
Dino-Era Vomit Fossil Found in England
Study Paints New Picture of Dinosaur's Nose
Skeleton of New Dinosaur "Titan" Found in Madagascar
"Tidal Giant" Roamed Coastal Swamps of Ancient Africa
"Feathered" Fossil Bolsters Changing Image of Dinosaurs
Oddly Angled Teeth Make Masiakasaurus Stick Out
New Find: Pterosaur Had Strange Crest, Fishing Style
Dinosaur Beak Probably Used to Strain Food, Not Kill Prey
Additional Dinosaur Resources from National Geographic:
RELATED LESSON PLANS
Use this National Geographic News article in your classroom with these Xpeditions lesson plans and student activity:
K-2: Dinosaur Bodies
3-5: How Do Scientists Find Dinosaur Fossils?
6-8: The Science of Digging Up Dinosaurs
9-12: The Evolution of Dinosaurs Over Geologic Time
K-2: Those Fussy Dinosaurs!
9-12: Physical Characteristics of Places: The Fossil Record
Activity: A Dinosaur's Neighborhood
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