Ask anyone to name some dinosaurs. Chances are, they will mention Velociraptor right after the mega superstar T. rex. All over the internet, we can hear the sound of hearts breaking when people find out that the sickle-clawed predator was no bigger than a turkey, and likely just as fluffy.
Little did they know, its all-American cousin Utahraptor, is actually as large as the oversized monsters from Jurassic Park.
Comparable to an adult bear in size, this 6.5 meter (21 ft) long hunter is the largest known member of the Dromaeosaur family, popularly known as raptors. In life, it would be taller than the average person today. The largest Utahraptor specimen discovered so far had a 22 cm (8.7 in) long sickle claw, a feature that would make it a fearsome hunter.
Size comparison of well-known dromaeosaurs and an adult human by Gabriel Ugueto
Back in 2001, a graduate student reported his sighting of a single bone, protruding from a rock bed in Utah. When paleontologists tried to excavate the bone, they kept hitting another bone, and another, and another. It turns out, that particular protruding bone led to the discovery of multiple other individuals buried together in close proximity.
At least six Utahraptor specimens, ranging from juveniles to adults, have emerged from this peculiar block. By looking at these fossils, researchers have noticed that they started out slender and agile, then grew up to be bulky, formidable hunters. Even when the bones are still embedded in the slab, they already show a different side of the animal that we didn’t know before.
It is rare for dinosaurs to be found fossilized together. When it happens, their death usually captures a unique snapshot about their lives. A graveyard of this scale, especially containing such a rare species, is like a treasure trove for paleontologists. In an attempt to grasp the full story of the dinosaurs, the whole nine-ton slab was excavated from the ground and moved to a lab in 2014. Jim Kirkland, the Utah State Paleontologist who gave Utahraptor its name in 1993, claimed it to be the most exciting discovery of his life.
Also trapped between the fossilized predators, were the bones of a herbivorous dinosaur. Was this place a petrified hunting ground? Did they hunt in packs as some movies want us to believe?
By looking at the surrounding rocks, Kirkland hypothesized that the unlucky herbivore found itself sinking in the middle of a quicksand pool. Attracted by the sight of an easy meal, multiple Utahraptors jumped into the scene, leading to their own eventual demise.
An illustration of the scene frozen in time by Julio Lacerda
If correct, this hypothesis explains why the predators, normally thought to be solitary hunters, died huddled together in such a big number.
However, it can only be tested by inspecting the fossils in greater details. For example, if the limbs of the animals are found to be tangled together, it’s a good sign that the animals hunted together. By looking at how much the bones were exposed by the sun, researchers can determine if the raptors all died at once or at different times.
The answer to this mystery may not emerge in the coming years. As powerful as they were in life, the Utahraptor fossils are delicate objects that require time and special skills to prepare.
This big undertaking requires Scott Madsen, a professional fossil preparator, to meticulously chip the block with needles to reveal the bones. Don DeBlieux, Assistant Utah State Paleontologist, will also create a 3D mapping of the block as Scott progresses. This kind of imaging allows researchers to better reconstruct the scene of their death.
Scott Madsen and Don DeBlieux jacketing the block with plaster and burlap, image by The Utahraptor Project
