Colorado’s bustling thoroughfare 98 million years ago was the Dinosaur Freeway.
More than 350 newly discovered tracks, made by various dinosaurs, crocodiles and a few pterosaurs, were identified at the site, which is now the John Martin Reservoir in Bent County, Colorado. When added to previously found tracks there, the total number of fossilized prints is well over 1,000. The dinosaur freeway is described in the February issue of Cretaceous Research.
"The Dinosaur Freeway runs from Northeast Colorado, near Boulder, to east central New Mexico, near Tucumcari," co-author Martin Lockley told Discovery News. "It is a trampled zone in Cretaceous rocks representing an ancient coastal plain like the present day Gulf of Mexico."
Lockley is a professor of geology at the University of Colorado Denver and serves as director of the Dinosaur Tracks Museum. He and colleague Reiji Kukihara found and analyzed the animal tracks.
An ornithopod dinosaur that was probably an Iguanodon-like species made the most common prints. Iguanodons were bulky, large, plant-eating dinosaurs, with some having large thumb spikes that were possibly used for defense against predators.
Based on the prints, other travelers along the Dinosaur Freeway included armored Ankylosaurs and ostrich-like dinos that were probably ornithomimids.
"Sometimes the ornithopod dinosaurs appear to have walked in herds," Lockley said. "Their trackways are parallel and equally spaced, and sometimes they all belong to individuals of similar size."
Swim tracks for large crocodiles, some over 13 feet long, were also found near the Dinosaur Freeway.
Lockley explained that, back in the dino day, the freeway was the coastal plain to the Cretaceous Western Interior Seaway, which ran north to south and split North America during this period of time.
"It was riddled with waterways and wetlands ideal for crocs," he said. "The crocs were not wimpy."
Dinosaurs therefore probably sped on by, likely migrating to find new forage. The animals may have traveled in groups by age. Juvenile and subadult dinosaurs were more dominant in the south, accounting for almost half of all identified tracks in that region. The proportion of juveniles sharply reduces in the middle area, and almost disappears in the north.
Lockley shared that other similar dinosaur thoroughfares have been discovered in Utah and Switzerland, both dating to the Jurassic Period.
"They mainly show that dinosaurs roamed very freely and for long distances along coastal plains," he said.
Spencer Lucas, curator of paleontology at the New Mexico Museum of Natural History and Science, told Discovery News that he believes "the conclusions of this article make eminent sense. They follow up on decades of careful research by Lockley and his collaborators on the track sites of what he calls the "Dinosaur Freeway."
Lucas added, "Significantly, the rocks in question yield very few fossil bones, so what we know about the extinct ecosystem — dinosaurs, pterosaurs, etc. — comes to us from the footprint record."
Lockley and Kukihara hope that future investigations will reveal even more tracks, helping to shed further light on the freeway and dinosaur behavior during the Cretaceous.