When Less Is More
Part of the Dinosaurs: Ancient Fossils, New Discoveries exhibition.
Sometimes tracks are readable and sometimes they're not. The texture of the ground surface and the number of animals that passed by are among the things affecting our ability to interpret what was going on when the tracks were made. While tracks of an animal traveling alone in one direction can be clear, even experts can't always tell whether multiple overlapping prints belonged to a group of dinosaurs traveling together or solitary animals revisiting the same site.
Stomping Ground
Raised tracks like these are called "negatives." They are not the direct imprint of the animal's foot, but the sediment that filled that footprint. Negatives are exposed when geological forces overturn and then fracture the rock. To visualize the process, imagine what happens when a baker turns a cake out of a pan. In that case, you see the bottom of a cake. In this case, you see a "worm's-eye view": the bottom of the trackmaker's foot.
Mapping a Stomping Ground
Scientists often make and publish tracings of tracksites so others can study them. The tracksite on display was traced and colored to highlight each clear print.
Straight and Narrow
Fossil footprints confirm that theropods had narrow bodies and kept their feet close to the midline as they walked, the way we do. Had their feet been widely spaced the animals would have been slightly unbalanced, and we might detect this in their footprints. The slightly "pigeon-toed" stance of some theropods adds to stability.
Dinosaurs, Living and Extinct
Birds are living dinosaurs, so studying the way large, modern ground birds--ostrich, emu and rhea--walk and run helps scientists interpret extinct theropod footprints. Experimenters encourage birds to walk across a footprint-friendly surface, such as moistened potter's clay, then photograph and measure the results. But as more than one researcher has found, convincing these excitable animals to walk on cue can be a challenge.
Walk Like a Dinosaur
Some large living ground birds--wild turkeys, for example--have footprints much like those of extinct dinosaurs.