Utahraptor: The Salty Saga of a Killer Dinosaur

By: Mark Mancini  | 

Utahraptor
The first fossils of the Utahraptor weren't discovered until 1975. At the time, paleontologists weren't sure what to make of them. Kostyantyn Ivanyshen/Getty Images/Stocktrek Images

Full disclosure: We're a little jealous of the 9,600-odd people who live in Grand County, Utah. You see, their home is the only place in the world where scientists have ever found the remains of an astonishing, bear-sized predator.

We're talking about Utahraptor. A carnivorous dinosaur with frightful claws, it lived around 135 million years ago and boasts a few "Jurassic Park" connections.

Yet by various estimates, Utahraptor could grow to be 15, 18 or perhaps even 23 feet long (i.e.: 4.65, 5.48 or 7 meters long). That made the dino a whole lot bigger than any "raptor" in Stephen Spielberg's filmography.

And as far as we know, its fossils are totally unique to Grand County.

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Land of the Lost

Utah is prime dino-hunting country. Fossils representing more than 115 dinosaur species have been unearthed inside the state's borders. Most of those species weren't identified until recently — as in, within the past 29 years. Truly, this is a golden age for paleontology in the Rocky Mountain West.

The eventual home of Jazz basketball and the Great Salt Lake looked very different when Utahraptor reigned.

Some 135 million years ago, the Jurassic Period of Earth's geologic history came to a close. It was followed by the Cretaceous Period, which lasted until a mass extinction event broke out 66 million years before the present. That calamity killed off the last of the dinosaurs (excluding birds).

Utahraptor lived early in the Cretaceous. At that time, the face of Utah was transforming, thanks in no small part to everyone's favorite pretzel topping: salt.

Without it, we might not know that Utahraptor ever existed.

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Time Plus Salt

Way before the first dinosaurs showed up, there was a deep basin along what's now the Utah-Colorado border. Seawater flowed in and left behind giant piles of salt that were literally thousands of feet (ie: hundreds and hundreds of meters) tall.

Rocky debris later covered up the salt beds. As time passed, the now-underground cache of salt started getting deformed by this heavy overlying material.

Parts of Utah's terrain were raised up by the shifting salt. Other spots went through a subsidence process and became naturally depressed.

Grand County was one of those places where below-ground salt movement — or "salt tectonics" — created big depressions across the landscape. Early in the Cretaceous, they became the home of vibrant ponds and lakes.

It was a perfect environment for future fossils.

North America was a fairly dry place in those days, and erosion was rampant. But here, the inflow of water and sediment to low-elevation lakes did a good job of covering up and preserving the bodies of dead animals.

Dead animals like (for instance) the late, great Utahraptor.

Utahraptor
The first Utahraptor fossils on record were discovered by paleontologist Jim Jensen of Brigham Young University in 1975. This Utahraptor skeleton is part of BYU's Museum of Paleontology.
Wikimedia/(CC BY-SA 4.0)

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Flora and Fauna

The two oldest assemblages of Cretaceous dinosaurs in the entire North American fossil record are both preserved in Grand County rocks. Again, we have salt tectonics to thank for that.

"About 135 million years ago, local subsidence in Grand County, uniquely preserved a series of lakes and ponds [teeming] with lungfish, chainmail covered bony fish, and spiny sharks," Utah's official state paleontologist James "Jim" Kirkland says via email.

Utahraptor was an important member of that ecosystem. There were plenty of other dinos around to keep the beast company. "Utahraptor stalked iguanodonts and young sauropods, while the heavily spined and armored Gastonia looked on," Kirkland says.

Iguanodonts were beaked animals, sauropods were long-necked giants and Gastonia was a type of armor-plated dinosaur built like a living tank. All of them had vegetarian diets. "Flowering plants had not appeared on this landscape dominated by conifers, cycads and ferns," Kirkland explains.

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Meet the Raptors

Want to impress your pals? When you go see "Jurassic World: Dominion" this summer, call the raptors by their formal scientific name: dromaeosaurs.

"Utahraptor was the largest and most massively built dromaeosaur," Kirkland says. With an estimated weight of 617 to 800 pounds (280 to 362 kilograms), he says the creature would have rivaled a "[large] black bear or small grizzly" in size.

As for the infamous Velociraptor, it likely weighed in at just 83 pounds (38 kilograms) or so.

That's not a typo. A native of Late Cretaceous Asia, the real Velociraptor was a small-bodied predator far removed from its Hollywood namesake. The raptors in the "Jurassic Park" franchise were inspired by the larger dromaeosaur Deinonychus.

Don't expect Sam Neill to issue a correction anytime soon, though.

In typical dromaeosaur fashion, Utahraptor had an outsized, sickle-shaped claw on each foot. These were held upright as the animal walked.

Both claws included a core of bone measuring up to 8.7 inches (22 centimeters) long. And that's just the tip of the iceberg. Like modern eagles, Utahraptor must have had keratin sheaths covering its claw bones.

Experts say they made the weapons even bigger than a naked skeleton might suggest.

A Utahraptor's arsenal was rounded out with long, claw-tipped arms and a mouthful of serrated teeth. All the better for tearing flesh.

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Cretaceous Park

Technically, the first Utahraptor fossils on record were discovered by paleontologist Jim Jensen of Brigham Young University in 1975.

However, nobody knew quite what to make of these until a team led by Kirkland dug up another set of raptor bones in 1991.

Utahraptor got its official name when Kirkland and his colleagues published a paper introducing the animal in 1993. Fittingly, that's the same year "Jurassic Park" stomped into theaters.

The creature's full scientific name, Utahraptor ostrommaysi, salutes dromaeosaur expert John Ostrom and animatronics creator Chris Mays (who'd helped the research effort). Scientists considered calling the dino "Utahraptor spielbergi" after a certain movie director, but that never came to pass.

Poor Utahraptor has yet to appear in any "Jurassic Park" film as of this writing ("Jurassic World: Dominion" is still a few weeks away).

On the small screen, the dromaeosaur did play a supporting role in an episode of the BBC's "Walking With Dinosaurs" TV series. Then there's "Raptor Red," a 1996 novel about a group of wild Utahraptor written by dino expert Robert Bakker.

Utahraptor
A track hoe pulls the 9-ton (8.2 metric-ton) field jacketed "megablock" from the Stikes Quarry in eastern Utah. The megablock contains the remains of at least one adult Utahraptor, 10 juveniles and three babies.
Utah Geological Survey

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The Dinosaur Trap

Real-world discoveries have upstaged the fiction. Utahraptor remains are known from four different localities across Grand County. One of these sites has yielded a 9-ton (8.2 metric-ton) sandstone "megablock" filled with assorted dinosaur bones.

According to researchers, this is probably what's left of a Cretaceous graveyard where dinos were trapped in a quicksand-like substance.

Some iguanodont bones are included in the mix, but the real highlight is the raptor material. Kirkland says the block has yielded fossils from "dozens" of individual Utahraptor. And in a stroke of luck, many of those dromaeosaurs are babies or juveniles.

That could bring us a few steps closer to understanding how the fearsome predator grew up.

By the start of 2021, fossil preparators had spent more than 3,500 hours working on the block, delicately exposing bone after bone. Anyone interested in making a donation to support their efforts can get the details over at the Utah Geological Survey's official website.

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