Image: Rich Penney, Sandia National Laboratories FAMILY of Parasaurolophus dinosaurs, with their strange hornlike crests, grazes by a swamp in Cretaceous New Mexico.

Click here for links to download the cry of the Parasaurolophus.

It's 75 million years ago, and you are somewhere in what is now the San Juan Basin of New Mexico. At the edge of a misty swamp, a family of dinosaurs munches on the leaves of nearby plants. The adults are almost 25 feet long and have strange mouths resembling duckbills. Even more curious, large, hornlike crests rise from the tops of their skulls. The biggest dinosaur abruptly stops feeding and looks your way. He raises his crest into the air, takes a deep breath and suddenly the earth is shaken by a deep rumbling cry of warning.

The eerie sound you just heard (if your browser supports RealAudio) is not the work of a Hollywood audio engineer taking a wild stab at re-creating a saurian bellow for the Jurassic Park soundtrack. Instead it may very well come extremely close to reproducing the actual voice of a Parasaurolophus (PAIR-uh-SOAR-uh-LOW-fuss) dinosaur.

Scientists at Sandia National Laboratories and the New Mexico Museum of Natural History and Science in Albuquerque produced the low-frequency sound by analyzing computerized tomography (CT) scans of a fossilized Parasaurolophus skull and simulating, on powerful computers, the sounds its internal passages and cavities would produce if air were blown through them like a musical instrument.

Image: Randy Montoya, Sandia National Laboratories DIGITAL PALEONTOLOGISTS Carl Diegert of Sandia (left) and Thomas E. Williamson of the New Mexico Museum of Natural History and Science simulate the call of the "trombone dinosaur."

Parasaurolophus is a member of a group of duck-billed dinosaurs known as hadrosaurs--large, plant-eating dinosaurs that lived during the Late Cretaceous (100 million to 65 million years ago). Some hadrosaurs, such as Parasaurolophus, bore large, hollow crests on their heads and are referred to as lambeosaurs. The fossil making this simulation possible was discovered in August 1995 by a crew headed by Thomas E. Williamson, curator of paleontology at the New Mexico Museum of Natural History and Science. The 4.5-foot-long skull is one of only five ever found, and it is the most complete, lacking only the segment below the eyes; the bony crest was extremely well preserved (see sidebar).

The precise function of the Parasaurolophus's crest has long been a puzzle to paleontologists. Some believe the feature served to help the dinosaurs recognize one another or as a display during mating, much like a peacock's plumage. The fact that the crest is riddled with long passageways that connect to the animal's respiratory system also suggested to researchers that it served as a "radiator" to shed excess heat. Others speculated that the crests were acoustic resonators, capable of producing distinctive sounds. The latter idea and the unique shape of the crests led researchers to nickname Parasaurolophus the "trombone dinosaur."

David Weishampel of Johns Hopkins University first analyzed the potential vocal abilities of Parasaurolophus. He constructed simple plastic models of the crest to demonstrate that they could amplify low-frequency sounds. But Williamson sought further proof, so he turned to Carl Diegert, a computer scientist at nearby Sandia National Laboratories. Diegert is part of a group that creates complex, three-dimensional computer models for simulating problems that cannot be subjected to real-world tests.