Monday, November 16, 2015

Dakotaraptor: Beast of the Week

This week we will be checking out a recently published dinosaur.  Say hello to Dakotaraptor steiniDakotaraptor was a meat-eating dinosaur that lived in what is now the South Dakota, United States, during the very late Cretaceous Period, 66 million years ago.  From snout to tail it was about eighteen feet long, and was a member of the dromaeosaurid family, which also includes Velociraptor and Deinonychus, to name a few.  When alive, Dakotaraptor would have shared its habitat with many famous dinosaurs like Tyrannosaurus, Triceratops, Pachycephalosaurus, and Ankylosaurus.  The genus name, Dakotaraptor, translates to "Dakota Thief/Hunter" in reference to where it was found.

Dakotaraptor chasing a pair of Anzu, a large kind of late oviraptorosaur it coexisted with, by Christopher DiPiazza.

Dakotaraptor is an exciting find because for a dromaeosaurid, it was huge!  Few dinosaurs from this family get to the size that Dakotaraptor did.  Like other members of its family, Dakotaraptor had a retractable, sickle-shaped claw on the second digit of each foot, which would have been kept up, away from the ground unless it was being used to dish out damage, in which case it cold rotate forward, like a switchblade. These talons were each over nine inches long and may have been used for piercing deep wounds into prey, or possibly for slashing wide lacerations.  Many believe they could also have been for pinning struggling smaller prey in place while the Dakotaraptor used its blade-like, serrated teeth to strip off small pieces of meat.

Photograph from DePalma's paper showing the different toe claws of Dakotaraptor.

In addition to the sharp teeth and giant claws, Dakotaraptor had a number of other important features to its anatomy.  The legs were particularly long, and lightly built.  This implies that Dakotaraptor, despite its size, was a very fast runner.  This is more similar to what you would see in smaller members of its family.  The larger dromaeosaurids, like Utahraptor, tend to be more robust, with shorter, thicker legs.  Sadly, other than teeth, none of Dakotaraptor's skull was ever found (yet) so we can only guess based on its closest relatives like Deinonychus or Dromaeosaurus, what it looked like in that region.

Dakotaraptor would have had feathers in life.  We can determine this based on the fact that multiple other members of its family have been discovered with feathers intact like Microraptor or Sinornithosaurus.  If that's not good enough evidence for you, it is important to note that the arm bone, called the ulna, of Dakotaraptor was found with evenly spaced little bumps on it.  These bumps are called quill knobs and are are present in modern birds as attachment sites for long, primary feathers.  Quill knobs have also been found on other prehistoric dinosaurs, like Velociraptor.

Diagram and photographs from the same paper showcasing Dakotaraptor's quill knobs on its ulna, proving that it would have had feathers in life.

Dakotaraptor is an important find because it helps fill out our image of the community of dinosaurs that inhabited North America 66 million years ago, by adding a fast-moving, medium-sized predator to the already diverse mix.  Before Dakotaraptor, all the predatory dinosaurs known from that area were either extra huge, in the form of Tyrannosaurus, or much smaller, like Troodon, or a smaller kind of dromaeosaurid, called Acheroraptor.  Until now we assumed that juvenile Tyrannosaurus were taking on this niche.  Now we know they had more competition!

That is all for this week!  As always feel free to comment below or on our facebook page!

References

DePalma, Robert A.; Burnham, David A.; Martin, Larry D.; Larson, Peter L.; Bakker, Robert T. (2015). "The First Giant Raptor (Theropoda: Dromaeosauridae) from the Hell Creek Formation.". Paleontological Contributions (14).

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