The smaller prints, with their three-toed impressions, are the traces of a theropod, a meat-eating dinosaur that walked on its two hind feet. The larger ones, so well preserved that they contain impressions of the dinosaur's toes, were almost certainly left by a plant-eating sauropod dinosaur, like Apatosaurus. The hind feet of these colossal dinosaurs measured one yard in length and three-quarters of a yard in width.

The footprints in the Glen Rose Trackway were saved through an unusual combination of events. They were originally made in soft mud, which was soon covered by silt that had filtered through quiet water. Millions of years later, inland seas covered parts of Texas, leaving sediments that buried the footprints deeper still. Within the last few thousand years, the Paluxy River eroded the sediments away and exposed the mudflat, with its superbly preserved footprints. A trail such as this offers scientists information about how dinosaurs stood and how they moved.

The Glen Rose Trackway was collected in 1938 by Roland T. Bird, who was in Texas looking for dinosaurs and other fossils for the Museum. Since the trail led into the river, part of it was either underground, underwater, or both. With a large work crew, Bird excavated the trackway and divided it into three sections, one of which you see here. The others are at the University of Texas and the Smithsonian Institution.