A dino 'dance floor'

A passel of natural potholes in a sandstone formation along the Arizona-Utah border testifies not to the erosive power of water on rock. Instead, two geologists from the University of Utah argue that the oddly shaped depressions are evidence of a sauropod version of the salsa.

In what they call the dinosaur dance floor, the team says that the depressions in the rock actually are footprints that creatures laid down some 190 million years ago, when the region was part of the supercontinent Pangea. At the time, the scientists say, sand dunes at the site covered a region larger than the Sahara. The dance floor likely was an oasis where migrant dinosaurs stopped for water and food.

The "trample surface" in the Vermilion Cliffs National Monument covers roughly three-fourths of an acre and contains at least 1,000 footprints, as well as markings indicating that some animals were literally dragging their tails by the time found water. Several dinosaur-tracks sites have been found in the West, as well as in places like Connecticut's Dinosaur State Park, where prints date to roughly the same period. The Vermillion Cliffs site, however, seems to have the highest concentration of them all. The duo, led by University of Utah geologist Marjorie Chan, says it has identified at least four groups of dinosaurs. The team has spotted three-toed eubrontes (the name of the footprints, not the critters that left them), tracks from two-legged therapods known as grallators, prints from long-necked sauropods, and signs from yet another group of therapods that grew to between six and 13 feet long.

The results appear in the current issue of the journal Palaios.