Most complete tyrannosaur fossil in Southwest excavated in Utah

The dinosaur's bones, including its toes, upper jaw and snout, can be seen protruding from the sedimentary rock in Grand Staircase-Escalante National Monument. Scientists estimate more than 75 percent of the skeleton is intact, the most complete of tyrannosaur fossil ever recovered in the Southwest United States. Photo by Mark Johnston/NHMU

Oct. 21 (UPI) — Paleontologists have completed the excavation of a 76 million-year-old tyrannosaur fossil in Southern Utah.

With approximately 75 percent of the dinosaur’s bones preserved, the fossil is the most complete tyrannosaur skeleton recovered from the American Southwest.

The fossil took a total of five weeks — and roughly 2,000 to 3,000 people-hours — to excavate, three weeks in May and two weeks in October.

“By the end of the second week, we had exposed enough to show that nearly all of the skeleton was still in the rock,” Randall Irmis, an associate professor of geology and geophysics at the University of Utah, told UPI.

Irmis is also the curator of paleontology at the Natural History Museum of Utah, where the fossil is now housed. In the lab, scientists will begin removing the rest of the rock from the fossilized bones.

The newly excavated fossil is one of several dinosaurs found inside southern Utah’s Grand Staircase-Escalant National Monument. The fossil was found in 2013 by Alan Titus, the monument’s resident paleontologist.

According to Irmis, Titus’ discovery happened the way most fossil finds happen.

“When we’re looking for new sites, where the rocks are exposed, we’re basically hiking around looking for new pieces of bones sticking out of the rock,” Irmis said. “He saw part of vertebrate sticking out of the rock and could see that most of the bones were still there.”

Researchers believe the dinosaur was buried by a shifting river channel or flash flood, preserving the skeleton in sediment.

The early evidence suggests the fossil belongs the tyrannosaur species Teratophoneus curriei, but paleontologists won’t know for sure until the skeleton is fully exposed.

“The features of the skeleton that allow one to identify the species are very specific,” Irmis said.

The skull shape is one of the most helpful indicators, but it could be several months to a year before the skull is completely exposed.

Researchers believe the fossil represents a sub-adult tyrannosaur, between 12 and 15 years old and measuring between 17 and 20 feet in length.

“When we put this specimen in combination with others that we’ve found, we’re going to get a really good sense of the different growth stages from juvenile to adult,” Irmis said.

Future analysis will help scientists better understand how the dinosaur’s physiology changed as it matured — whether the tryannosaur got faster or developed a more powerful bite as it matured.

Such a well-preserved and complete skeleton can also help paleontologists answer questions about the species behavior and biology.

“We can look at things like reconstructing the muscles, we can look at the bone that surrounded the brain and get a sense of which parts of the brain were structurally supported and likely to have grown larger than other parts,” Irmis said.

The most famous tyrannosaur is, of course, T. rex. And most tyrannosaurs, including T. rex, have been discovered to the north — most often in the Dakotas, Wyoming and Alberta, Canada.

But more attention is now being paid to the tyrannosaurs of the Southwest.

Teratophoneus curriei and its peers emerged some 8 to 15 million years before the first T. rex showed up, but the latest specimen could help scientists better understand the relationships between the two species.

In fact, southern tyrannosaur species are some of the closest in relation to T. rex.

“The more complete specimens we have too study, the more information on each species’ anatomy we have, the more we’re able to fill in the details of the family tree,” Irmis said.


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