In the Late Cretaceous period, 72 million years ago, a warm and shallow sea divided North America into two landmasses, one to the east and the other to the west.
The area known today as Mexico was the southernmost tip of a peninsula-like landmass called Laramidia.
The arid desert terrain where the dinosaur was recovered in the early 1990s looks nothing like the humid estuary that existed there 72 million years ago.
Many of the dinosaur bones found in the area have been buried together with snails and clams, indicating that the animals inhabited environments near the shore.
"This type of site is relatively common in Coahuila, but we are still trying to understand why," said Gates, the study lead author.
"Opening the door to the world of the dinosaurs requires not only figuring out how the animals lived, but also how they died.
"Much of our future work in Mexico will focus on deciphering the various bone beds that have been discovered," added Gates, whose research was partially funded by the National Geographic Society. (National Geographic Society owns National Geographic News.)
The researchers have also found large bone beds containing other duck-billed and horned dinosaur skeletons in the area.
The scientists speculate that powerful storms may have devastated the region at times, killing off entire herds of dinosaurs.
(Read related story: "Did the Rise of Germs Wipe Out the Dinosaurs?" [January 15, 2008].)
A large assemblage of dinosaur tracks in the area suggest it was home to many species of dinosaurs, the most common having been duckbills, which scientists know sometimes congregated in large groups.
However, scientists note, the many different dino species do not seem to have been as widely dispersed as was expected.
"Not long ago, we would have predicted that the same dinosaur species would be found throughout such a small landmass—less than one-fifth the present-day size of North America—but the emerging picture is strikingly different, with coexisting species of giant animals restricted to relatively small areas," said Sampson, the co-author.
"In addition, there appears to be plenty of species evolutionary turnover—that is, species came and went at a relatively rapid rate with life spans [of] less than a million years."
Most hadrosaurs known to have lived in North America in this period have been found in Alberta, Canada.
"One of the things we are trying to find out is how the dinosaur communities of Canada differed from those that lived at the same time in Mexico," said Don Brinkman, of the Royal Tyrrell Museum of Paleontology in Alberta.
Brinkman is studying the non-dinosaur vertebrates found at the Mexican site.
"With this discovery, we are starting to see how the dinosaurs that lived in these regions are different.
"Once we understand [these] patterns at a single time, we hope to start tracking how these patterns change with changing climate," he added.
Philip Currie is a paleontologist at the University of Alberta in Edmonton who was not involved in the study.
"The description of the new crested hadrosaur is particularly cool because it is related to forms in Canada and Asia, and will change some of our ideas about the southern distribution of these animals," Currie said.
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