Because dinosaurs had feet at the ends of their limbs and traveled with them, evidence of their locomotion is preserved as tracks and trackways. A track is the impression left by a foot in a sediment or other substrate, although some two-legged dinosaurs also made "hand" (forelimb) impressions, which are also considered as tracks. Tracks are preserved in two main ways: (1) as impressions (negative relief), which are molds of the original foot; and (2) as casts (positive relief) made by overlying sediments into the original impressions. Some dinosaurs were also heavy enough to deform layers of sediment below the surface; such impressions (and their overlying casts) are called undertracks because they were under the original track surface.
A trackway is two or more consecutive tracks made by the same animal. Many mammals and birds leave a walking trackway that shows an angle between the footprints from a midline of travel; some trackers refer to this progression as diagonal walking. All dinosaurs seemingly were diagonal walkers. Dinosaur trackways show no evidence of either tail or belly dragging, meaning that dinosaurs walked erect with their limbs underneath their bodies, rather than sprawled to the sides of the body.
Dinosaurs either traveled on two rear feet (bipedal) or four feet (quadrupedal). If a dinosaur was obligated to walk on two feet (such as humans) for most of its life, then it was an obligate biped; an obligate quadruped spent most of its life on four feet. If a dinosaur could walk on two feet (similar to modern bears) but spent most of its time on four feet, it was a facultative biped but an obligate quadruped. Accordingly, a normally bipedal dinosaur that could have gone onto all four limbs was a facultative quadruped. (I hope you are now thoroughly confused, because I was the first time I encountered these terms. Just reread the explanation again until it makes sense.)
Different types of dinosaurs left distinctive tracks that can be attributed to general classifications (ceratopsians, theropods, ornithopods, sauropods) but tracks rarely give enough detail to identify the genus or species of the trackmaker (e.g., Tyrannosaurus, Apatosaurus, Triceratops). Nevertheless, tracks and trackways, because they are nearly always in-situ records of dinosaur behavior, represent valuable information about what dinosaurs lived in an area during certain times, how they evolved, how individuals behaved, and how they interacted.
This foot belongs to Allosaurus, a large Jurassic theropod. Notice the three toes with a relatively narrow width. The skeleton is mounted at Dinosaur National Monument, northeastern Utah, USA.
This foot belongs to Tyrannosaurus, a large Cretaceous theropod. Although separated by millions of years, both Allosaurus and Tyrannosaurus would have left similar footprints that were attributable to large theropods. Foot is from a replica mounted in Western Colorado's Dinosaur Valley, Grand Junction, Colorado.
This theropod track is in the Morrison Formation (Jurassic) of eastern Utah. Notice the greater depth of the track in the toe region, which suggests a horizontal posture for the dinosaur while it was walking.
This track, in the Entrada Formation (Jurassic) of eastern Utah, shows only a partial impression and is probably an undertrack. However, a deep claw impression is visible on the far left toe, probably indicating a shift of the theropod's weight to the left.
The trackway shown here was on a dislodged block of sandstone from the Wingate Formation (Jurassic), eastern Utah. The right-left bipedal progression along a narrow midline, in addition to the footprint shape, is characteristic of theropods.
Ornithopods were also capable of leaving bipedal trackways but were mostly facultative bipeds. Their tracks are similar to those of theropods in that they frequently show a three-toed pattern; they differ from theropod tracks in the width of the individual toe prints, which are greater than those of theropods. Ornithopod tracks are present in deposits from the Jurassic through the Late Cretaceous but are particularly common in Late Cretaceous deposits. Hadrosaurs are probably the best known ornithopods that left tracks attributable to the trackmaker.
This is a typical ornithopod foot (a hadrosaur), showing the widely splayed three-toed anatomy. Skeleton is in the Museum of Western Colorado's Dinosaur Valley, Grand Junction, Colorado.
This ornithopod track was cast in the bottom of a sandstone bed, hence you are looking at the bottom of the footprint in positive relief. Track is in the Museum of Western Colorado's Dinosaur Valley, Grand Junction, Colorado.
The side view of the same ornithopod track depicted previously shows some pressure ridges in the central toe area, caused by the forward motion of the animal when it was walking.
The large size attained by some ornithopods late in the Mesozoic Era is shown by this Late Cretaceous ornithopod print, with my sandaled foot (size 9, men's) for scale. This track is also preserved as a sandstone cast, so you are looking at the bottom of the footprint.
The front foot of a quadrupedal animal is called the manus, whereas the back foot is called the pes. Quadrupedal dinosaurs seemingly walked like most diagonal walkers do nowadays, by moving the right manus and left pes at about the same time, alternating with the left manus and right pes. Trackways show the manus print slightly in front of the pes print on each side of the trackway.
Prosauropods, ceratopsians, ankylosaurs, and possibly stegosaurs left four-toed impressions in their tracks, both for the manus and pes. Sauropods have five-toed tracks for their pes impressions but do not show toes in manus impressions. Some quadrupedal ornithopods have three-toed tracks for their pes impressions but manus prints do not show obvious toes, either. Excellent examples of quadrupedal ornithopod prints are preserved at Dinosaur Ridge, just west of Denver, Colorado.
This sauropod print is of a right pes and is one track in a trackway. The tip of my field boot is the scale in the lower lefthand corner. The mud "push-ups" in the front of the track (toward the top of the image) and to the right indicate the shifting of the sauropod's weight forward and to the right. Locality is in eastern Utah, Morrison Formation (Jurassic).
This trackway, to which the previously depicted sauropod print belongs, registers a rarely recorded event; a sauropod that changed its direction of travel abruptly to the right. The progression of the sauropod was from the lower lefthand corner to the upper righthand corner of the picture. Both manus and pes prints are visible in the image. (If you look closely to the lower right, a theropod track is pointed in a direction perpendicular to the sauropod trackway.)
Further Reading on Dinosaur Tracks and Trackways:
Lockely, M. G. 1991. Tracking Dinosaurs: A New Look at an Ancient World. Cambridge University Press, Cambridge, 238 p.
Lockley, M. G., and Hunt, A. P. 1995. Dinosaur Tracks and Other Fossil Footprints of the Western U.S. Columbia University Press, New York, 338 p.
Thulborn, R. A. 1990. Dinosaur Tracks. Chapman and Hall, London, 410 p.