Like fingerprints for a crime detective, dinosaur footprints are valuable clues for scientists who study life on prehistoric earth. Paleontologists (PALE-ee-un-TOL-uh-jists) examine the fossilized impressions and remains of ancient living things.
Dinosaur tracks help them figure out how real-life "Barneys" walked, stalked, ran, and lived when they roamed the earth millions of years ago.
The scientific study of footprints is fairly new, says James Farlow, a paleontologist who specializes in ichnology (ick-NOL-uh-jee), the study of footprints. For more than 150 years after the first fossilized footprints were discovered in New England in 1802, such tracks were simply a subject of fanciful guessing. Some said they were made by large extinct birds. Others thought native Americans had carved them. (Hopi Indians in America's West pictured dinosaur footprints in paintings and clothing.)
Trails tell tales
Today, the study of those footprints is helping to answer some difficult questions about dinosaurs: How far and how fast did they travel? Were they solitary animals or did they live in herds like buffaloes? You can't answer these questions just by looking at dinosaur bones.
"Footprints tell us about the kind of animal that made them, how they walked. Did they waddle, or were they efficient walkers?" Dr. Farlow says.
You might wonder how dinosaur tracks were preserved for 200 million years. For a footprint to survive, it must be made on sediments (mud) found in and near lakes and rivers, says ichnologist Anthony Martin. "Sediments act as fine-grained wet cement," he says.. "Once a footprint is made, it has to dry out fast enough and it will have to be buried." It also must be undisturbed for a few millennia until it fossilizes (turns to stone).
Farlow maps the footprints he finds. He also takes pictures, measures the distances between footprints, and sometimes makes plaster molds of them. He also looks for bones, eggs, nests, tooth marks, and even droppings.
Many dinosaur footprints look like large bird tracks - especially the tracks of the modern-day Australian emu. (In fact, emus look very prehistoric, and some of the birds "played" dinosaurs in the 1993 movie "Jurassic Park.") Other prints are more like elephant or hippo tracks. The round footprints of long-necked, plant-eating sauropods can be up to a meter (39 inches) across.
How fast did they go?
When humans walk, our footprints are neat and leave a complete and fairly level impression from heel to toe. But when we run, we go up on our toes. So did dinosaurs. Complete, level footprints indicate that the creature was walking. Running animals take longer strides and leave partial prints.
Using formulas, scientists can estimate how fast dinosaurs ran. The tyrannosaur in "Jurassic Park" supposedly went 35 miles per hour. No way, Farlow says. "A safe [top] speed would be around 22 miles [per hour]. If they ran at 40 miles [per hour] and stumbled, they would be seriously injured, just like dropping a watermelon from a third floor."
Tracks of dinosaurs also open a window on their social lives. Tracks found in Bandera, Texas, and other places indicate that sauropods were social creatures. They left many tracks that are side by side, indicating that they moved together in a group. To Farlow, this proves that sauropods lived in herds.
Sorry, no hopping dinosaurs
Dinosaur footprints have also set right many myths and misconceptions. First, dinosaurs never dawdled. They walked efficiently. And there was a time when people speculated that hopping dinosaurs existed. But after careful review of the "hopping" tracks, scientists concluded they actually had been made by swimming turtles.
And did you ever see an old science-fiction movie in which dinosaurs drag their heavy tails along the ground? Ah, but dinosaur trackways hardly ever show marks made by dragging tails, Farlow says. The absence of such markings led scientists to revise their images of dinosaurs. "It is difficult to drag a tail," Martin Lockley wrote in his 1991 book "Tracking Dinosaurs" (Cambridge University Press), "and tough on the tail as well."
Dinosaur track sites to visit:
*The Alameda Parkway Dinosaur Ridge near Denver. Dubbed "the dinosaur freeway," the site has hundreds of footprints. Tours are available.
*The Appleton Cabinet in Amherst, Mass. A monument to the father of ichnology, Edward Hitchcock, the museum contains the world's largest and best-documented collection of footprints.
* Dinosaur State Park, near Glen Rose, Texas.
Elementary-school students might enjoy "On the Tracks of Dinosaurs: A Study of Dinosaur Footprints," by Dr. James Farlow (Franklin Watts, 1991). Dr. Lockley's "Tracking Dinosaurs: A New Look at an Ancient World" is for high school and up.
On the World Wide Web, try:
Make a Dinosaur Trackway
James Farlow of Indiana University-Purdue University helped us draw the outline of what the left footprint of a tyrannosaur might look like. Tyrannosaurs lived about 100 million years ago. Some of the two-legged meat-eaters grew to be 15 to 18 feet tall and 50 feet from nose to tail.
You can get an idea of how big a tyrannosaur was and how it moved by making a trail of its footprints. You'll need big pieces of paper (30 by 15 inches), a ruler with centimeter markings, a yardstick, scissors, a pencil, and a tape measure.
On a sheet of paper, draw an enlargement of the grid that's on the footprint at left. Make each square on your grid 10 cm by 10 cm (about 4 inches square). Copy the footprint's outline onto your grid.
Cut out your life-size pattern and make as many copies as you like. These are left footprints. Turn over half the copies: Now you have some right footprints, too.
The stride of a tyrannosaur (or any bipedal dinosaur) is five to seven times the length of its foot. Begin your trail by putting down two left footprints in a line 13 feet, 7-3/4 inches (420 cm) apart. Place a right footprint halfway between the two lefts. Now move the right footprint to the right 14-1/2 inches (37 cm). (See diagram above.) Copy this spacing for the other footprints. Whew! This guy is big!
Trigonometry fans (or those with protractors) can calculate the track for other bipedal dinos based on scientists' observations about the trails: The ratio of stride length to foot length works for big and small bipedal dinos; three footprints made sequentially describe an isosceles triangle that contains a 155-to-160-degree angle.