Utahraptor Fossil crates Largest Raptor 

Utahraptor ostrommaysi (Kirkland et al., 1993)
Pronounced “You-Taw-Rap-Tore Oh-Strum-Mays-eye’’
Means “Ostrom Mays Utah Thief”
Named for its discovery location of Utah
Lived during the Early Cretaceous 139-130 mya in Utah, North America

Utahraptor was arguably the most dangerous pound-for-pound dinosaur that ever lived. Over 20’ long and approach 1,000 pounds, this largest, and oldest, of the dromaeosaurids (“raptors” of movie and book fame!) had it all: large teeth with a powerful bite, powerful arms with sharp claws, and the largest of all the “killing claws”, the famous pedal ungual II (in paleontology terms, which means the second toe claw) that was held off the ground so it would be always sharp! Add in excellent vision and the ability to generate quick bursts of speed and an absolutely lethal predator is born! Utahraptor was the apex predator of its day, meaning it was the largest meat-eater around. It had numerous prey items to choose from: Gastonia, a nodosaur, sauropods like Cedarosaurus and Moabosaurus, the therizinosaur Martharaptor, and iguanodonts such as Cedrorestes and Hippodcraco. It is thought the animal ambushed these beasts (all of which were larger and heavier than itself), using its hugely powerful legs with sharp claws to kick, while gripping with its long, powerful arms and ripping off chunks of flesh with its sharp teeth.

Utahraptor is famous because of its gigantic “killing claw”, over 9” in length when one considers the claw would have been covered in a keratinous sheath, making it even sharper too!


In the early 90s Dr. James Kirkland realized he had discovered a new-to-science dinosaur and a big one at that! Utahraptor was named as the movie Jurassic Park came out. The movie depicted Velociraptor as being a 12’+ long, 300+ lbs dinosaur when in reality a Velociraptor is very small, 6’ long and 30 lbs tops (think of a turkey with a long tail). Even the largest known raptor at the time, Deinonychus, was 11’ long and weighed 200 lbs, making the movie raptors substantially larger. That is until Utahraptor was announced, the size of which dwarfs those in the movies!

A few of the big debates about Utahraptor include did it hunt in packs and did it have feathers. The pack-hunting evidence is thin at best for its cousins and there is no pack hunting evidence at all for Utahraptor. No direct feather evidence has been found for Utahraptor, the assumption of feathers comes from the fact some of its closest relatives, like Velociraptor, Dakotaraptor, and Microraptor, have been found with feather evidence such as quill knobs.

If you look closely at the hand claws you will see they are actually… foot claws! When the original skeletons were made for casting the hand claws weren’t well understood and a toe claw was inadvertently used for the hand claw. Recently definite Utahraptor hand claws were discovered and they are quite different, being thicker, shorter, and even more recurved than the foot claw.

Utahraptor Fun Fact: Its species name was initially ostrommaysi and was meant to honor John Ostrom, famous paleontologist, and Chris Mays, Dinamation founder. However, in 1999, it was changed to ostrommaysorum, citing the International Code of Zoological Nomenclature (ICZN) rules. In 2019 it was changed back to ostrommaysi based on a new ICZN ruling. That is why you might see two different spellings for its species name, there is in reality only one known species.