Everything you know about Utahraptor hands is wrong!

Utahraptor, the Early Cretaceous apex predator of Utah and the largest dromaeosaurid "raptor" ever discovered, is mounted with toe claws on its hands!

 

Utahraptor hand claw

Toe Claws on its hands! (Toe claw on bottom right side of image)

 Utahraptor toe claws pedal ungual

Utahraptor toe claws (note similarity to hand claws)

Known from multiple locations in southern Utah, Utahraptor material is entirely disarticulated, meaning none of its bones were found attached to each other.  Instead it was found in what I lovingly refer to as a "bone salad", a scenario where over 20 big animals died and were on the surface for quite awhile and thus scavenged and subjected to rainstorms, wind, and trampling, only to be buried in a flash flood.  It is relatively easy to identify individual bones belonging to nodosaurids versus iguanodontids versus sauropods versus theropods, but when working on entirely new animals it becomes more difficult to know which claws go to which sized individual, or in the case of Utahraptor, which claws went on the hands versus the foot!

When Utahraptor was named in 1993 the very first identifying character used was its giant hand claws.  In 2001 it was learned that the large hand claws are actually toe claws, the hand claw had a much different morphology, very recurved, resembling a meat hook, rather than the slashing blades on display around the world.  This conclusion was confirmed in 2007 by a study that provided instructions on how to differentiate the hand from toe claws.  Using this knowledge a second hand claw of Utahraptor was identified!  

 

Utahraptor hand claw manual ungula

Notice how recurved it is!

 

Utahraptor toe claw pedal ungual

Not as recurved as the hand claw

 

What we don't know is which hand claw goes with which toe claws. We don't know how large the hand claws were as the two known hand claws are small and might go to a small individual.  However, they could go to a larger individual, which would indicate it had much smaller hand claws than we believed it had.  Until we find one articulated we won't know for sure.  Our best hope is the megablock being worked on in Salt Lake City!

Utahraptor captured the world's imagination when it was named due to its massive size.  Up until it was announced, the largest known dromaeosaurid was Deinonychus.  An enterprising author visited Dr. Ostrom, the man that named Deinonychus, and saw how amazing it was, armed with its "killing claw", a massive second toe claw that was kept off the ground so as to be perpetually sharp.  Dr. Ostrom also showed this author, Michael Crichton, another killing machine, the tiny (25 lbs or so) Velociraptor.  Crichton took the name Velociraptor, made it even larger than Deinonychus, and wrote a best-selling book that became a movie released June 9, 1993.  The public gushed over the effects, and the amazing "raptors", and thus was born a massively successful franchise that put dinosaurs front-and-center to an adoring world. 

Enter Utahraptor!  Paleontologists were quick to dismiss the fact the Velociraptors in the movie were larger than the largest at-the-time known dromaeosaurids (= raptors to the public), and were especially disappointed to see Velociraptor, one of the smallest of these animal types, to have been made so large.  Then, June 18, 1993, only 9 days after the movie came out, Utahraptor was published, making the on-screen "raptors" small fries in comparison to this 20'+ long, 1,000 lb. + gigantic killing machine.  When it was published it had the largest hand claws of any dinosaurs outside of the therizinosaurs, and the largest killing claw of any animal ever discovered!  

We now know the hand claws on the mount, and the ones named to be a unique feature of Utahraptor, are actually toe claws, and the hand claws were smaller and, in many ways, even more terrifying as they have a meat hook/fish hook quality to them, being so recurved that they would have gripped and ripped flesh off in large, deep chunks.  The bony core of these images were, in life, covered with a keratinous sheath making them upwards of 40% longer!  And much, much sharper.

 

Bibliography

Original description of Utahraptor by Kirkland et al. (1993)

Paper showing how to tell the Utahraptor hand and foot claws apart by Phil Senter (2007)

 

 

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