Sunday, March 30, 2014

Nanuqsaurus: Prehistoric Animal of the Week

This week we shall be checking out a newly discovered and described dinosaur, Nanuqsaurus hoglundiNanuqsaurus was a tyrannosaurid, closely related to Tyrannosaurus, Tarbosaurus and Lythronax, that lived in what is now Alaska during the late Cretaceaous about 69 million years ago.  Even though only parts of the skull have been discovered, it can be estimated that Nanuqsaurus would have measured around eighteen to twenty feet long from snout to tail and like all known tyrannosaurids, it was a meat-eater.  The genus name, Nanuqsaurus, translates to "Polar Bear Lizard" because it was discovered in Alaska...where Polar Bears live.  It sounds cute.  Go ahead say it out loud...Nanuqsaurus.  Aw.

A Nanuqsaurus pair overlooks a herd of Pachyrhinosaurus (probably too big to be prey). By Christopher DiPiazza

Every time a new species of dinosaur is covered in the media, it is given some flashy description to grab the attention of readers.  In the past the media, and in some cases the paleontologists themselves, have referred to new dinosaurs as "vampire-porcupine" (It was a plant eater and no quills were found on the actual specimen.  A related dinosaur had feather-like quills which were not sharp in life...stretch much?), a "chicken from hell" (It was from an area called the Hell Creek Formation but basically most biggish feathered dinosaurs are compared to chickens for some reason.), and if it's a large theropod you better believe it will be compared to T. rex in some way especially if there was even the slightest chance it could have been bigger.  So what have they dubbed poor Nanuqsaurus?  A "dwarf tyrannosaurus from the arctic"

Is this nickname another annoying headliner or is there truth to it?  Well let's start with the arctic part.  It was definitely living in Alaska which we can agree is cold right now but was it during the Cretaceous?  Well back then, just like now, there were long periods of continuous night and long periods of continuous day in the poles.  There were also seasons back then in certain parts of the world but they weren't as dramatic as they were now.  Where Nanuqsaurus was, during the winter time, it definitely got cold, but it probably wasn't as frigid or snowy as it is now in Alaska and the summers would have been pretty warm, even hot.  That brings up another question: was Nanuqsaurus even staying in what is now Alaska all year round or did it migrate south to warmer areas during the winter?  The answer to that question is uncertain but the scientific paper describing the new species seems to favor the idea that Nanuqsaurus stayed there all year round even through the long, dark winters.  The reason for this has to do with the second part of the nickname, "dwarf".

Hey Nanuqsaurus, maybe you should just...let it go.

Let me just say that I personally don't see Nanuqsaurus as a "dwarf" tyrannosaur.  Yes, it was much smaller than its close relative, T. rex... but is that really saying much?  Tyrannosaurus was amongst the biggest meat-eating dinosaurs at over forty feet long!  Other close relatives of both of these animals are around the same size as Nanuqsaurus, but were never referred to as dwarfs.  Dryptosaurus, Alioramus, and Teratophoneus(assuming it was not a juvenile) were all about the same size as Nanuqsaurus.  There are also many tyrannosaurids that were only slightly larger than that.  Maybe it's because that despite all this, Nanuqsaurus is considered even closer to the giant tyrant lizard than other tyrannosaurids were.  The new scientific paper describing Nanuqsaurus by Anthony Fiorillo and Ronald Tykoski states that the remains of Nanuqsaurus that were found were from an adult, and not a juvenile that still had growing to do, according to the pieces of the skull that were examined closely.  I briefly spoke with paleontologist and friend of the site, Dr. Thomas Holtz, who is an expert on tyrannosaurs, about Nanuqsaurus' proposed dwarfism.  He is still speculative of the discovered Nanuqsaurus being an adult.

"I don't think we can confidently say that this is really even a dwarf tyrant. They didn't have that much material, and certainly not the bones (limb bones) you would want to truly say it had reached full size.)"- Thomas Holtz


The known remains of Nanuqsaurus from the paper by Fiorillo and Tykoski.  Despite the fact that it isn't much, they were able to determine after close examination that this is indeed a new genus and species.

 If we give the paper the benefit of the doubt and say that just looking at the skull, we're assuming it was an adult until legs are found, what does being small have to do with toughing out long winters?  According to the paper, Nanuqsaurus evolved a smaller body size so it could survive on less food which would have been more scarce during the winter.  HOWEVER, looking at modern animals, a larger body size is actually more common in animals that inhabit cold environments.  A larger body means less surface area to volume ratio and therefore more heat conservation.  This is called Bergman's Rule.  You can see examples of Bergman's Rule in things like polar bears (larges species of bear), lots of the giant ice age mammals, and the largest, cold-blooded reptiles which can remain active for longer periods of time without heat than their smaller cousins.  In fact, there is another dinosaur, a still unnamed species of Troodon that lived in the same relatively cold time/place as Nanuqsaurus that was bigger than all of its relatives (Troodontids are typically pretty tiny)!  So what's the deal with Nanuqsaurus?  Bergmann's rule doesn't always hold true, especially if there are other factors to take into consideration.  In the case of Nanuqsaurus, like the paper said, it would have needed to eat during the winter and being slightly smaller than its giant southern cousins could help as long as it wasn't too small to the point where it couldn't keep warm anymore.  Remember, like I said earlier, Nanuqsaurus wasn't really that small at a whopping twenty feet long!    It appears that Nanuqsaurus and the giant Troodon had both evolved towards a middle range that was best suited for whatever it was like in Alaska back then.  Nanuqsaurus also probably had feathers to help with insulation so there's that too.
   
Famous last words.

So what do we get out of all of this?  Was Nanuqsaurus truly a "dwarf tyrant from the arctic"?  It was definitely living in an environment that was cold-ER part of the year but not nearly as cold as modern winters...and the specimen that was dug up would have been around twenty feet long.  Whether you consider that a dwarf or not, the length is what it is.

Join us next week for another Prehistoric beast!  As always feel free to comment below or on our facebook page. Also special thanks to Dr. Holtz for taking the time to speak with me about this animal and giving the whole post his expert approval!

References

Fiorillo, A. R.; Tykoski, R. S. (2014). "A Diminutive New Tyrannosaur from the Top of the World". PLoS ONE 9 (3): e91287. doi:10.1371/journal.pone.0091287.

 Fiorillo, Anthony R.; Gangloff, Roland A. (2000). "Theropod teeth from the Prince Creek Formation (Cretaceous) of Northern Alaska, with speculations on Arctic dinosaur paleoecology". Journal of Vertebrate Paleontology 20 (4): 675–682. doi:10.1671/0272-4634(2000)020[0675:TTFTPC]2.0.CO;2.

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