Gorgosaurus: Beast of the Week

Today we will look at a famous meat-eater known from lots of well-preserved fossils that has helped us understand a lot about tyranosaurs over the years.  Check out Gorgosaurus libratus!

Gorgosaurus was a meat-eating dinosaur that lived in what is now Alberta, Canada, and Montana, USA, during the late Cretaceous period, between 76.6 and 75.1 million years ago.  From snout to tail adults could grow up to 30 feet (9 meters) long.  The genus name translates to "Dreadful Reptile".  The species name, libratus, translates to "balanced".

Life reconstruction in watercolors by Christopher DiPiazza of a pair of Gorgosaurus libratus.

Gorgosaurus was a member of the tyrannosaurid family, often described as a slightly smaller, more gracile relative of Tyrannosaurus.  Like all tyrannosaurids, Gorgosaurus had a series of chisel-like teeth in the frontmost portion of its jaws that are rounded in the front, but flat in the back, giving them a D-shaped cross section.  These could have been an adaptation for scraping meat off bones.  The rest of Gorgosaurus' teeth were curved, thick in cross section, and serrated for cutting flesh.  Gorgosaurus possessed large, round eye sockets and likely had good vision in life.  It also had rough textured bone running down the top of its snout and a small, forward-facing, horn over each eye.  There was likely keratin growing over these parts of the skull in life, giving the dinosaur a more ornamented look than the skull shows.  The presence of horns on the snout and over the eyes is actually a trait common to many tyrannosaurs.  We don't know exactly what these structures were for in life, but they very well may have been for some kind of interaction within the species, either for display only or perhaps some sort of physical combat for dominance between rivals.  

Gorgosaurus skeleton on display at the Royal Tyrell Museum in Alberta, Canada.

Like all tyrannosaurids, Gorgosaurus had proportionally short arms and only two functional fingers on each hand.  It's legs, however were proportionally long and powerful, implying it was a strong distance walker and probably a fast runner in life.  Since we also have juvenile Gorgosaurus specimens on the fossil record, we know that when younger, the legs were even longer, proportional to the body, implying the younger individuals were even faster.  Because there are relatively numerous Gorgosaurus specimens in the fossil record of varying life stages, scientists were able to figure out just how fast this dinosaur grew.  It turns out that tyrannosaurids, like Gorgosaurus, continued to grow their entire lives, but went through extremely rapid growth spurts during certain parts and slowed down once reaching mature adult sizes, the fastest of these spurts they would have gained about 110 pounds in a single year!  It was also found out that Gorgosaurus spent about half of its life at juvenile size.  This has supported the idea that tyrannosaurids specialized in hunting smaller faster prey when young, and then moved on to slower, but tougher, prey when fully mature.  This also helps explain the lack of small-medium sized predators in communities where tyrannosaurids are found, because it was likely the tyrannosaurids were filling more than one predator niche depending on their maturity. 

Skeleton of a juvenile Gorgosaurus on display at the American Museum of Natural History in New York.  Note the long, slender legs.

Gorgosaurus is one of the few fossil dinosaurs scientists have been able to recover skin impressions from.  The patch of skin from Gorgosaurus would have been on the tail and shows fine, slightly raised bumps.  There is no way to tell if Gorgosaurus also had feathers or not in life since different forms of body covering can exist on different parts of an animal's body and also preserve under different conditions (for instance we have numerous dinosaur fossils that preserve feathers but no scales, yet we can infer they also had scales on certain parts of the body), but given that it is from the branch of dinosaurs that includes birds, called coelurosaurs, it very well could have.  

Photograph of Gorgosaurus skin impressions from Bell's 2017 paper.

Throughout the course of it's living on earth, Gorgosaurus would have coexisted with, and probably hunted, lots of other dinosaurs, including, but not limited to hadrosaurs, like Parasaurolophus, Lambeosaurus, and Corythosaurus, ankylosaurs, like Eouplocephalus and Anodontosaurus, and ceratopsians, like Chasmosaurus and Styracosaurus.

That is all for this week!  Feel free to leave a comment below!

References

Bell, Phil R., et al. “Tyrannosauroid Integument Reveals Conflicting Patterns of Gigantism and Feather Evolution.” Biology Letters, vol. 13, no. 6, 2017, p. 20170092., https://doi.org/10.1098/rsbl.2017.0092.

Erickson, Gregory M., GM; Makovicky, Peter J.; Currie, Philip J.; Norell, Mark A.; Yerby, Scott A.; Brochu, Christopher A. (2004). "Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs". Nature. 430 (7001): 772–775.

Lambe, Lawrence M. (1914). "On a new genus and species of carnivorous dinosaur from the Belly River Formation of Alberta, with a description of Stephanosaurus marginatus from the same horizon". Ottawa Naturalist. 28: 13–20.

Holtz, Thomas R. (2004). "Tyrannosauroidea". In Weishampel, David B.; Dodson, Peter; Osmólska Halszka (eds.). The Dinosauria (Second ed.). Berkeley: University of California Press. pp. 111–136.

Russell, Dale A. (1970). "Tyrannosaurs from the Late Cretaceous of western Canada". National Museum of Natural Sciences Publications in Paleontology. 1: 1–34.

Voris, Jared T., Zelenitsky, Darla K., Therrien, Francois, Ridgely, Ryan C., Currie, Phillip J., Witmer, Lawrence M. Two exceptionally preserved juvenile specimens of Gorgosaurus libratus (Tyrannosauridae, Albertosaurinae) provide new insight into the timing of ontogenetic changes in tyrannosaurids. Jou Ver Pal (2022).