The Continuously Evolving Picture of the World's Largest Raptor

When Jurassic Park stomped into theaters during the summer of 1993, audiences suddenly became familiar with predators of the past like Dilophosaurus and Velociraptor. Right around that time, real-life paleontologists were figuring out an even bigger velociraptor relative, a dinosaur that has become a rock star in its own right.

Back in 1991, Utah State paleontologist Jim Kirkland and his crew were excavating a bonebed outside Moab, Utah, brimming with dinosaur fossils dating back 125 million years. While excavating an armored dinosaur that would eventually be named Gastonia (in honor of fossil reconstruction expert Robert Gaston), Kirkland found something more: the front of a jaw from a theropod, the class of dinosaurs containing such meat-eaters as T. rex. “Later that same field season, we found a sickle claw,” Kirkland recalls. The shape was unmistakable: The recurved claw was a dead ringer for the characteristic foot claw of dinosaurs like Deinonychus and Velociraptor, only this one was much larger. “It was twice as big as the same claw on Deinonychus,” Kirkland says.

Kirkland and his collaborators tossed around different names. “Dinoraptor” was a contender. At one point, there was a suggestion that the species name should be “spielbergi” to court the Jurassic Park director for some funding support. But the paleontologists ultimately went in a different direction.

That claw would become the single fossil that characterized a new animal: Utahraptor ostrommaysi. Its journey from rare find to state dinosaur of Utah to inspiration for the NBA’s Toronto Raptors illustrates the difficult, treacherous way in which scientists try to unravel the colossal carnivores that once roamed the planet.

Utahraptor block being carried away for study in 2014.


(Jim Kirkland)

Many carnivorous dinosaurs live in scientific limbo for years. That’s because of the scarcity of fossils—simply put, large, predatory dinosaurs are rare, which makes sense from what we know about modern ecosystems. Plants will always outnumber herbivores, and herbivores will be more numerous than animals that eat them.

As luck would have it, though, a different team of paleontologists had stumbled upon Utahraptor decades before. In 1975, Brigham Young University paleontologist Jim Jensen collected a batch of theropod bones of about the same age from a nearby site called Dalton Wells. But few were fully prepared for study or described. They weren’t recognized as Utahraptor bones until years later when Kirkland recognized the similarities and the fossils were more fully-prepared.

Those bones made all the difference. Kirkland’s team had turned up a scant few bones from the jaw, foot, and leg at the new site. Based on the relationship of Utahraptor to other dinosaurs, the early representations of the dinosaur (including the journal description and an animatronic created for the Dinosaur Museum in Fruita, Colorado) depicted what was essentially a plus-sized Deinonychus. However, the Dalton Wells collection turned out to contain dozens of Utahraptor bones, enough to put pieces of multiple skeletons together to create a better version of the dino.

“Utahraptor is the largest dromaeosaur in the family,” says University of La Rioja paleontologist Angelica Torices. It is estimated to have stretched 23 feet long, weighed more than 600 pounds, and carried some deadly traits. “The claws on the hand seem to have been more specialized for cutting than other dromaeosaurs,” Torices says, and the teeth at the front of the lower jaw appear to angle forward farther than in other raptors.

Even so, Utahraptor probably used the same techniques that allowed most carnivorous dinosaurs to be efficient eaters. By studying various dinosaur teeth, Torices and colleagues found that carnivorous dinosaurs used a “grip and rip” feeding style. The dinosaurs would bite and pull backward, letting the serrations of their teeth do the work. Utahraptor probably chomped the same way.

Block containing utahraptor fossils


(Jim Kirkland)

In the new century, new finds changed our image of Utahraptor again.

In 2001 a graduate student roaming around Moab spotted what initially looked like a human arm bone in an area of Early Cretaceous rock layers. The remains turned out to be more Utahraptor, and not an isolated bone or skeleton this time. When Kirkland and his team dug in, they unearthed dozens of Utahraptor bones from multiple individuals, from yearlings to full-grown adults, encased in a nine-ton block of Cretaceous quicksand. It took years of work to excavate and transport the block, but this collection contained the potential to provide a clearer view of Utahraptor than any of the earlier bonebed finds.

Excavations of the block are still underway, but we know it contains hundreds of bones, including skulls from three yearlings, five juveniles and one adult. Paleontological work is slow and exacting, but especially so in this case because the bones are tiny. The premaxilla (the front of the upper jaw) of a baby Utahraptor is about the size of a penny, for example.

The big bones, too, bring surprises. Adult Utahraptors were not 20-foot-long versions of Velociraptor, but much bulkier animals. “The new limb bones are 50 percent more massive than the same-sized Allosaurus bone,” Kirkland says, indicating that Utahraptor was more burly than slender. The skulls, too, look more like what you’d expect of a small tyrannosaur than a swift snapper.

Also, Utahraptor would have been fluffy. Recent discoveries connected to related dinosaurs including Velociraptor suggest Utahraptor would have been covered in feathers—a more elegant animal than the scaly renditions of dinosaurs common in the 1990s.

The Moab site might illuminate details of Utahraptor behavior as well. The nine-ton sandstone block containing the fossils appears to be a quicksand trap. The dinosaurs became stuck and were buried by the sloshy sediment that killed them. It’s unclear whether the animals were trapped at the same time or over a longer span, but the examination of how the bones are arrayed and the age of each Utahraptor might dovetail with evidence from tracks that some raptors were social and lived in groups.

Utahraptor Ridge, Utah.


(Jim Kirkland)

All of these threads have made Utahraptor a Cretaceous celebrity. During the 1990s, the Toronto Raptors got their logo inspiration from Utahraptor and the dinosaur was the subject of the “paleofantasy” Raptor Red. Utahraptor has become such a dinosaur fan favorite that 10-year-old Kenyon Roberts was able to bend the ear of Utah state senator Curt Bramble and convince him that Utahraptor should become the state’s dinosaur.

Just one problem: Utah already had a state dinosaur. The Jurassic predator Allosaurus had been selected because of the huge amount of Allosaurus bones from more than 48 individual animals that had been uncovered in eastern Utah’s Cleveland-Lloyd Dinosaur Quarry.

It was a 21st-century dinosaur showdown. Some Utahans felt the state didn’t need a new state dinosaur and didn’t want to push aside part of the state’s fossil history. So a compromise was struck: In a 26-0 vote conducted in 2018, Utahraptor was made Utah’s state dinosaur and Allosaurus was shifted to be the state fossil. The Mesozoic meat-eaters were able to coexist as state symbols.

Utahraptor may be poised to jump to even greater fame. A proposal to preserve the Dalton Wells quarry as Utahraptor State Park recently ran through the Utah legislature. Unfortunately, the bill became a bit stuck—not unlike the dinosaurs themselves from the quicksand block. but when asked if there is still hope for the proposal, Kirkland says “Absolutely!”

Utah is rife with dinosaurs, but this super-sized raptor seems to be a cut above.

#Nature | https://sciencespies.com/nature/the-continuously-evolving-picture-of-the-worlds-largest-raptor/