Diggin' For Dinosaurs - Dinosaur Ridge & Dry Mesa Quarry
Although the environment here changed from the Jurassic to the Cretaceous periods, it remained a prime place for dinosaurs. The most spectacular evidence for this comes about halfway down the eastern side. A rocky snapshot from the distant past, captured in Cretaceous sandstone, consists of 37 different trackways comprising 335 individual footprints made as dinosaurs, some alone, others in groups, strolled along the shore.
This is the "Dinosaur Freeway," a possible migration route stretching several hundred miles from Boulder, Colorado, to New Mexico, the trackways record the passage of carnivorous, ostrich like dinosaurs, and plant-eating Iguanodon-like ones. Six of the trackways were made by the meat eating ornithomimids with three toed, nine inch long prints. These bipedal dinosaurs apparently traveled alone.
Larger three-toed tracks, between nine and 18 inches long, were left by at least eight iguanodontids, both juveniles and adults from 12 to 20 feet long that walked on all four limbs. Based on the distance between their prints, the two ton herbivores who probably moved at a slow walk, about two miles per hour.
Although the iguanodontids were moving in several directions, expert analysis suggests that they occupied groups of similar sized animals: strong evidence of social behavior. For example, among the larger animals at least two pairs appear to have traveled absolutely parallel. And three other animals stuck close to the shoreline itself, if not in lockstep then certainly as part of a group.
At Dinosaur Ridge, seven different layers of Dakota sandstone contain dinosaur tracks. Extrapolating from the density found here and at other sites in the corridor between Boulder and New Mexico, experts estimate that the 30,000 square miles of territory along the mountain front could contain 240 billion tracks, though most would still be buried. The shore of the Western Interior Seaway may have been the site of epic dinosaur journeys.
Dry Mesa Quarry, Colorado
Considering the size of the dinosaurs whose bones have been found at Dry Mesa Quarry in western Colorado, including the 100-foot-long Supersaurus and the 35-foot-tall Torvosaurus, the place itself seems rather small at first glance. Rounding the last bend of a quarter-mile hiking trail, one comes upon not an expansive quarry but a bone-white gash cut into a hillside. The diminutive scale of the excavation makes sense, however, when it is understood that dinosaurs may have arrived here in a flood-induced "bonejam."
Downstream, at the site of the current Dry Mesa dig a skeleton probably got caught in the braided channels of water, and like a logjam, everything piled up behind it. Indeed, 150 million years after the flood, researchers pulling apart the bonejam have found remains of more than two dozen species of animals, allowing Dry Mesa to claim the most diverse fauna of any Morrison Formation site in the United States. Mixed with the jumble of dinosaur bones, scientists have found turtles, crocodiles, lungfish, mammals, and a flying reptile. To date, they have recovered more than 4,000 bones but never a complete skeleton, giving credence to the theory that the disarticulated pieces were all washed there by a flood.