Monday, February 27, 2012

A New Look at Killer Claws

I recently read a scientific paper that really made me think about a certain group of dinosaurs in a new way and hopefully after reading this (and the actual paper which I will link at the bottom) you will as well.  The dinosaurs I am referring to are the ever popular dromaeosaurs, or as they are referred to more casually, "raptors".  I personally hate using the term "raptor" when referring to this type of animal since the word, "raptor", really is supposed to be used to describe modern birds of prey like hawks and their relatives.

The paper had to do with a new theory on how dinosaurs like Velociraptor and Deinonychus (dromaeosaurs) used their trademark switchblade-like killing claw to deal with their prey.  If you are not familiar with what I am referring to allow me to briefly explain.  Dromaeosaurs (and to a lesser extent, Troodontids) have a special modified toe on each of their hind limbs.  Digit two (counting from the inside out.  Digit one is the reduced hallux/dewclaw) of each foot wields a HUGE curved claw that looks like a sickle or a hook.  This toe is also retractable like a cat's claws so when not in use, it can be held up off of the ground as to not get dull while the animal walks or runs around.  Still confused?  Check out my sketch below.

The theory that has been generally accepted with regards to the use of these claws is that the dromaeosaur would use them to stab or slash prey to death.  Many times dromaeosaurs are showcased in art and media hunting in packs to overwhelm much larger, slower animals. Shown below is a quick sketch I did of two Deinonychus doing exactly that to a poor Tenontosaurus.

This article, however, proposes a different theory and it all starts with something I touched on last month: looking at modern animals for reference.  When dealing with dromaeosaurs, the first living animal that comes to mind is a bird.  After all, birds are dinosaurs themselves and further more, are theropods just like dromaeosaurs.  Dromaeosaurs in particular were very bird-like even amongst other extinct dinosaurs in that they have very similar skeletal structures to birds as well has having had feathers according to many fossil discoveries.  So what kind of bird are we talking about here?  Many times when studying extinct dinosaurs, large, flightless birds are used for reference but in this case, because we are dealing with the dromaeosaur's special claws, raptors (birds of prey) take the center stage.  Ever get a close look at the foot of an eagle or a hawk?  Check out this photo below.

Notice anything interesting about the sizes of the talons on this bald eagle?  Okay now check out this other photo.

That one is from a South American bird called a Seriema that is more adapted to walking around on the ground than to flying unlike the eagle.  What they both have in common, however, is that over-sized claw on the toe just like an extinct dromaeosaur has! Now whether this is from the same gene that was present in a common ancestor between some modern birds and dromaeosaurs or just an example of good old convergent evolution I do not know.  (Remember convergent evolution from my post last month?)  Whats important to figure out is how these living birds use their special claws and apply this behavior to animals like Velociraptor and Deinonychus back in the Mesazoic.  As you may know, these modern birds don't really hunt in packs for the most part nor do they hunt prey too much larger than themselves (there are a few exceptions).  This claw is mostly used to pin down struggling prey while the sharp beak, which is hooked in the front and blade-like on the sides, tears off chunks of meat.  Think of it like using a fork and knife to eat a meal.  The fork holds down the food while the knife cuts off a bite-size piece.  Still can't visualize it?  No worries!  Once again my job at Outragehisss Pets comes to the rescue.  Below is a short video of our Eurasian Hawk, Gwen, using this exact method to eat a dead mouse while listening to some sweet tunes.  (She doesn't actually start to do the feeding behavior until about 1 min 50 sec in.  Feel free to skip ahead if you like.)

So what if extinct dromaeosaurs specialized in hunting smaller prey as opposed to pack hunting large prey?  Pretty cool idea I think.  Even though dromaeosaurs didn't have the beak of a modern raptor, they did have serrated teeth which would have worked just as nicely for tearing off small chunks of flesh.  The paper also talks about how they may have used their arm feathers to keep balance while immobilizing their victims much like modern raptors do today. 

Interestingly enough I did a painting of a Troodontid using a technique similar to the one proposed in the paper on an unfortunate boa constrictor (pictured above) before I had actually known about the paper itself.  Pictured below is a quick sketch I did special for this blog post of a Deinonychus using this technique on a smaller dinosaur. 

Hope you found this post interesting because I sure had a lot of fun writing it.  Also be sure to check out the actual article here.  Farewell until next time!

Works Cited

Fowler, Denver W., Elizebeth A. Freedman, John B. Scanella, and Robert E. Kambic. "The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds." PLoS ONE:. Museum of the Rockies and Department of Earth Sciences, Montana State University, Bozeman, Montana, United States of America, 14 Dec. 2011. Web. 27 Feb. 2012. <>.