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Ravell Call, Deseret Morning News
David D. Gillette stands with a mounted skeleton, made with molds of the original therizinosaur bones.

The skull of a new species of duckbill dinosaur, deemed "one of the most magnificent" ever found, was unveiled Wednesday, and the find provides important clues about the evolution of the large plant-eaters.

The Gryposaurus monumentensis, the species name reflecting its discovery in the Grand Staircase-Escalante National Monument, was a huge, rugged, thick-boned, 800-tooth plant-eater. It is one of three dinosaur species uncovered in Utah that are earning renown.

The Gryposaurus made its debut during a press conference Wednesday at Grand Staircase-Escalante and in the pages of the Zoological Journal of the Linnean Society.

"It was a monster," said Terry Gates, paleontologist with the Utah Museum of Natural History at the University of Utah.

Another species, the therizinosaur, was a sickle-clawed dinosaur uncovered in the badlands near Big Water, Kane County, and is the subject of a handsome new exhibit at the Museum of Northern Arizona.

And two new ceratopsid (horned) dinosaurs, also discovered at Grand Staircase-Escalante, are being introduced in Survey Notes, the journal of the Utah Geological Survey, by James I. Kirkland, Utah's state paleontologist, and the survey's Donald D. DeBlieux.

Experts said the Gryposaurus monumentensis was found several years ago by the Raymond M. Alf Museum of Paleontology, which is based on a high school campus in Claremont, Calif. Excavations were carried out in 2003, and difficult preparation work on the bones continued after that.

Overseeing the work was then-University of Utah graduate student Terry Gates, who is now a paleontologist at the Utah Museum of Natural History.

Gates said other species of the same genus Gryposaurus were discovered in the Canadian province of Alberta and in Montana. They were the dominant plant-eaters of the region, including Utah, 74 million years ago during the Cretaceous Era. But only 1 million years later, the time of the new find — still during the Cretaceous — the genus was extinct except in the Four Corners area.

Some change in the environment may have been the cause of the rapid change in dinosaurs.

This type of duckbill dinosaur had powerful jaws, making it the Cretaceous version of a "weed whacker," Gates said.

In life, it was about 30 feet long, including its 10-foot-long tail. The dinosaur stood at least 10 feet tall and boasted a three-foot skull.

Arizona exhibit

The Museum of Northern Arizona's new exhibit features a towering skeletal model of the clawed 93-million-year-old therizinosaur and was curated by David D. Gillette, a paleontologist at the museum.

The exhibit includes an arrangement of the bones as they were found near Big Water, colorful art illustrations by Victor Leshyk of what the creature may have looked like — including feathers — and videos about the discovery and excavation of the bones.

The first bones of the Utah therizinosaur were found in 1999 by Merle Graffam, a Big Water resident, in an otherworldly gray shale that area residents call "The Moon," said Gillette, who was Utah's state paleontologist from 1988-98.

The bones were very badly fractured and embedded in Tropic shale. The shale was mud when the dinosaur was alive, and over the years, layers of rock accrued and compressed the shale, fracturing the bones. Eventually, erosion stripped away the layers, and bits of the dinosaur were revealed.

But the therizinosaur is a land or shoreline creature. How did it end up far from a shore at the bottom of what was, 93 million years ago, a shallow interior seaway covering the middle of what is today's continent of North America? Was it grabbed by shoreline predators? Did its body float out to sea?

And there are other mysteries: What were its large, dangerous-looking claws for? Feeding? Defense? And did the creature have feathers?

"We suspect all carnivorous dinosaurs had feathers," at least in the early stages of life, Gillette said. When young, they may have needed feathers for thermal regulation, not for flight. The largest may have lost features in adulthood.

Dinosaurs fossils found in China seem to confirm this theory. A therizinosaur found in China is known to have had feathers, and although therizinosaurs are believed to have been plant-eaters, they probably had carnivore ancestors, Gillette said.

When erect, the Big Water therizinosaur would have been 13 feet tall and weighed about a ton.

New horned dinosaurs

The September issue of Survey Notes describes two new Utah horned dinosaurs, or Ceratopsids, from Grand Staircase. They were uncovered in the Wahweap formation, which is just below the Kaiparowits formation where the duckbill was extracted. They lived about 80 million or 81 million years ago.

The two fossils are called the Last Chance skull and the Nipple Butte skull. They were found in 2002 and 2001, respectively.

According to Survey Notes, these creatures are early relatives of the triceratops. The Last Chance skull, discovered and prepared by the survey's DeBlieux, is in especially fine condition, said Kirkland, and will be displayed Oct. 15 in the lobby of the survey's offices on North Temple Street in Salt Lake City.

"It's probably the oldest animal of its kind ever found, and it's certainly the most primitive," Kirkland said.

The skull shows signs of linkage with protoceratops dinosaurs from Asia, he said. Without its long horns, the skull would measure about three feet long. It was so large that, as in the case of the duckbill, "we had to airlift it out," he added.

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