A Mesozoic Moment
Over the space of a few minutes, on a single day 100 million years ago, about two dozen long-necked plant-eating dinosaurs crossed a mudflat. The smaller animals in the group trailed after the bigger ones. A large meat-eating dinosaur visited later.
All this information is in the tracks you see before you. Decoding what looks like a confusing jumble can be tricky. But as more and more trackways are unearthed, not just in Texas but in thousands of sites around the world, scientists are developing techniques for reading those hidden messages.
Davenport Ranch Tracksite
Researchers from the American Museum of Natural History uncovered a tracksite in 1940 containing prints made by four of the 23 sauropods and one of the three or more theropods at the site. In the illustrations, the sauropods are moving from right to left; the theropod, which arrived later, is moving left to right. Because some tracks shown in orange are on top of some shown in blue--in what's known as an overprint--we know that the "blue dinosaur" walked across the mud first. This huge tracksite preserving the trails of 23 sauropods was exposed, photographed and carefully drawn in 1940. Then the excavators covered it up to protect the tracks.
It was to those drawings that dinosaur tracker Martin Lockley turned in 1995 when he wanted to investigate herd behavior. Lockley examined the size, shape and direction of each sauropod print and overprint. When he could assign each set to a specific animal, he color-coded the results for easier interpretation. Lockley concluded that small and full-grown animals were indeed traveling together, with the small animals following in the tracks of the large ones--just as elephants do today.
Deep in the Heart of Texas
The Davenport Ranch tracksite is one of more than 40 such sites in the center of present-day Texas, spread throughout an area of 100,000 square kilometers (about 40,000 square miles). During the Cretaceous period, the region was a low coastal plain similar to the present-day coast of the Gulf of Mexico. The western United States from Boulder, Colorado, to northeastern New Mexico is also rich in tracksites; 100 million years ago that area was the western shoreline of an inland seaway.
Tracks Tell No Tails
The prints of 23 long-tailed plant eaters at Davenport include not a single tail track. These dinosaurs evidently kept their great tails aloft, not dragging in the mud!
What if you walked on all fours? Think how different the prints left by your hands would look from the prints made by your feet. The front and back prints of many animals--including sauropod dinosaurs--can be just as different. Among the long-necked plant eaters, the back foot was often three or four times the size of the front foot.