Troodontid (Alaskan): Beast of the Week

 This week we'll be checking out a unique member of the troodontid family of dinosaurs.  Let's check out the mysterious Alaskan troodontid!

The Alaskan troodontid was a likely mostly meat-eating dinosaur that lived in what is now Alaska, in North America, during the late Cretaceous period, about 69 million years ago.  From snout to tail it is estimated to have measured about 13 feet (4meters) long. 

This is the first dinosaur featured on Beast of the Week that doesn't have an official Genus and species name yet.  A formal scientific paper has yet to be published describing it, even though its known remains, consisting of teeth, are widely known.  

My life reconstruction in watercolors of a trio of the mysterious Alaskan troodontid.

Even though the fossil material is extremely scant, we know this dinosaur was almost certainly a member of the troodontid family of dinosaurs, like Pectinodon and Byronosaurus, because the fossilized teeth are curved and have extremely deep serrations, which is diagnostic for that group.  Troodontids were typically smaller, fast-running dinosaurs, that would have looked very similar to birds when alive.  What sets this Alaskan troodontid apart, however, is the fact that its teeth are much larger than those of its known relatives.  Using these teeth to predict the size of the rest of the animal, basing proportions off more completely known relatives, we end up with an unusually massive troodontid at about 13 feet long! To put it into perspective, Pectinodon, a more typically sized member of the family, was only about 6 feet long.  

The reasoning for this troodontid's large size is mostly a mystery.  Scientists predict it may have had something to do with its habitat, which if you might remember, was Alaska today.  During the late Cretaceous, Alaska wasn't as cold as it is now, but it was still significantly cooler for the time, compared to the rest of the world.  It also would have undergone long periods of darkness in the winter, just like it does today.  Perhaps having a larger body was an adaptation to the cold, since animals with larger bodies can retain body heat more easily.  On top of that, the Alaskan troodontid almost certainly had a coat of feathers that could have helped retain heat as well.  We can be fairly confident of this since we have fossils of other species of troodontid that preserved actual feathers and evidence of feathers.  

Skeletal mount on display at the Perot Museum in Texas.  Note the vast majority of this mount is guesswork based on other more completely known troodontids.

Like all known troodontids, this species likely would have had large forward-facing eyes, that would have allowed it to better hunt for small prey, possibly even at night.  We also know that troodontids had a strong sense of hearing thanks to enlarged middle ear cavities in their skulls.  At least some of them even had asymmetrically placed ears, an adaptation also present today in many owl species which allows them to better target moving prey in complete darkness or other situations where sight isn't an option.  

The Alaskan troodontid likely had long legs with a retractable toe, armed with a curved claw, on each foot.  This would have been an adaptation ideal for pinning down smaller prey, like mammals and possibly smaller/baby dinosaurs.  The teeth we know were serrated for slicing meat, although some have suggested troodontids may have supplemented their diet with plant material, too.  If this species was living in an environment that was cold and dark for months out of the year, food would have been scarcer, and more menu options would have been ideal anyway.  

When alive the Alaskan troodontid would have shared its habitat with the gigantic plant-eating dinosaur, Edmontosaurus, the ceratopsian, Pachyrhinosaurus, and it would needed to watch out for the tyrannosaurid, Nanuqsaurus.  

References

Castanhinha, R.; Mateus, O. (2006). "On the left-right asymmetry in dinosaurs". Journal of Vertebrate Paleontology. 26 (Supp. 3): 48A.

Currie, P. J. (1985). "Cranial anatomy of Stenonychosaurus inequalis (Saurischia, Theropoda) and its bearing on the origin of birds". Canadian Journal of Earth Sciences. 22 (11): 1643–1658.

Fiorillo, Anthony R.; Tykoski, Ronald S.; Currie, Philip J.; Mccarthy, Paul J.; Flaig, Peter (2009-03-12). "Description of two partial Troodon braincases from the Prince Creek Formation (Upper Cretaceous), North Slope Alaska". Journal of Vertebrate Paleontology. 29 (1): 178–187.