Nearly Complete Tyrannosaur Skeleton Found in Utah


Toe bones, the upper jaw and snout of the fossilized remains of a tyrannosaur skeleton found in Grand Staircase-Escalante National Monument. The skeleton is the most complete of its kind found in the Southwest United States. Mark Johnston/NHMU

Tyrannosaurus rex and its closest relatives comprised a family known as the tyrannosaurids. An awe-inspiring group, their ranks included some of the biggest land-dwelling carnivores of all time. They first appeared on Earth around 86 million years ago and would remain at large until a mass extinction wiped out the non-avian dinosaurs 20 million years later.

Tyrannosaur material has surfaced in both Asia and North America. Here in the Western Hemisphere, a century of big discoveries has made the family all but synonymous with one particular region: The Northern Great Plains. This sprawling, grassy frontier is a tyrannosaur-hunter's paradise. After all, the first partial T. rex skeleton ever found emerged in Montana back in 1905. And that was just the tip of the iceberg.

A smaller species called Albertosaurus sarcophagus was named after the Canadian province where a mass grave site— or bonebed — was discovered with 22 skeletons. Across the U.S. border, South Dakota was the final resting place of Sue, the most complete T. rex specimen ever found. Speaking of the Mount Rushmore State, Harding County, South Dakota has yielded so many Tyrannosaurus remains that it's been nicknamed "The T. rex Capital of the World."

Yet, American tyrannosaurs weren't restricted to the north; the beasts had a big presence in the Southwest, too. Paleontologists have found T. rex material in New Mexico, Colorado, Utah and Texas. Furthermore, it turns out that this iconic killer wasn't the first member of its family to inhabit the region. Since 2010, scientists have formally described three new tyrannosaurs — Bistahieversor, Lythronax and Teratophoneus — which all pre-dated T. rex and called the Southwest home.

The discovery of Teratophoneus in southern Utah's Grand Staircase-Escalante National Monument was announced in 2011. The new carnivore had an abnormally short skull for a tyrannosaur, but what really caught the media's attention was its striking genus name. Translated from Greek, Teratophoneus means "monstrous murderer." Pretty intense, right?

One of the paleontologists who co-authored the animal's scientific description was Dr. Thomas Carr, who told us a little bit about the moniker. "The name was suggested to us by a colleague who does not work on dinosaurs — Dr. Sean Modesto — but who has a talent for formulating striking [scientific] names," Carr says in an email exchange. "He suggested 'Teratophoneus' for us to consider, and the team took to it!"

Now, six years later, Teratophoneus is making headlines again. The University of Utah announced that the most complete tyrannosaur skeleton ever found in the Southwest has come to light. And paleontologists are fairly confident that it belonged to one of these "monstrous murderers."

The fossil, which is approximately 76 million years old, comes from the previously mentioned Grand Staircase-Escalante National Monument. So far, more than 75 percent of the skeleton — including most of its skull — has been accounted for. Scientists think the dino was buried — either in a river channel or by flood — which helped keep its skeleton intact. They suspect it was about 12 to 15 years old and 17 to 20 feet (5.1 to 6 meters) long at its death.

It was first spotted in 2015 by Alan Titus, a paleontologist who works for the Bureau of Land Management. The process of digging this thing up and transporting it to the Natural History Museum of Utah (where it's now located) was a herculean undertaking. Volunteers in the field spent somewhere between 2,000 and 3,000 man-hours excavating the skeleton, which was then airlifted out via helicopter. Another 10,000 hours of work remain to prepare the fossil for research.

A team from the Natural History Museum of Utah encase a tyrannosaur fossil in a plaster jacket while on an expedition in Grand Staircase-Escalante National Monument.
Mark Johnston/NHMU

Randall Irmis, the museum's curator of paleontology, says the skeleton looks very much like a Teratophoneus, but it can't be positively identified until the skull is fully prepared (with all the rock removed) in the lab. "If it isn't Teratophoneus," he says via email, "it would most likely be something new."

Should this in fact be a hitherto-unknown dinosaur, it would be in some good company. The Grand Staircase-Escalante National Monument is rife with dino species found nowhere else — including the flashy, horned herbivores Kosmoceratops richardsoni and Utahceratops gettyi.

Back when these animals were still breathing, Utah looked markedly different. At the time, the Arctic Ocean was connected to the Gulf of Mexico by a shallow, inland sea. This body of water ran through the heart of North America, splitting the continent in half. The result was two separate landmasses: An eastern expanse called "Appalachia" and a western one known as "Laramidia." Modern-day Utah sat on the latter, just a quick jaunt from the coastline. "It would have been very similar to the bayous of Southern Louisiana today, both in terms of temperature/humidity and landscape," Irmis says. A warm, wet floodplain, the area was covered by an intricate web of rivers and streams.

This find could shed a bit of light on a paleontological hot topic. The extent to which Laramidia's geography affected tyrannosaur evolution has been debated in recent years. During the early 2010s, some scientists suggested that a physical divide on the landmass separated the northern and southern species. But more recently, this idea has been challenged. According to exhaustive studies published in 2016 and 2017, the various tyrannosaurs of Laramidia were free to intermingle. Maybe the new skeleton will help clear things up a bit.

Fossil hunters have prospected the American West for well over 140 years now. Yet, even after all this time, blockbuster discoveries — like the new Grand Staircase tyrannosaur skeleton — are still being made out there. Who knows what'll turn up next.



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