Tuesday, August 18, 2015

Paleo-Profiles: Albertosaurus/Gorgosaurus

Author's note: Raptorrex here, thought I'd try something new out. Basically, Paleo-Profiles are biographies of prehistoric animals. More often than not, the animal addressed correlates to the previous post. Example: If I were to review a book about Tyrannosaurus, then the Paleo-Profile would be T. rex. The main goal of this project is to give information for school projects and such. Expect these to come once a month. 

Image Credit: Luis Rey

 Name: Albertosaurus 
Species: A. sarcophagus
Discovery: Osborn, 1905
Geologic era: Campanian of the Late Cretaceous
Geographic area: Canada/USA
Family: Tyrannosauridae of the suborder theropoda

Name: Gorgosaurus
Species: G. libratus
Discovery: Lambe, 1914
Geologic era: Campanian of the Late Cretaceous
Geographic area: Canada/USA
Family: Tyrannosauridae of the suborder theropoda

Albertosaurus, one of the best-studied tyrannosaurids to date, lived during the Late Cretaceous of North America, with a habitat ranging from Alaska all the way down to Texas. Like most other tyrannosaurs of its time, Albertosaurus is characterized by a sleek build, triangular horns above its eyes, and remarkably short arms. Based on current fossil evidence, we know that Albertosaurus (as well as Gorgosaurus) was a particularly common predator during its time. In Alberta, Canada, the Dry Island bonebed has allowed paleontologists to uncover more than 25 different individuals of varying age. Not only have the findings shown that Albertosaurus populations were abundant, it has also been a revolutionary change in the way tyrannosaur behavior has been proposed. The idea of tyrannosaurs living and hunting in packs was first hypothesized by Dr. Gregory S Paul in his book Predatory Dinosaurs of the World, alluding to the behavior of the big cats today. Actual fossil evidence for this hypothesis would be found in the late 90's by a team led by Dr. Philip Currie of the Royal Tyrrell Museum. At the very least, Albertosaurus lived in small families, possibly to protect their young.

Gorgosaurus (bottom) and Albertosaurus (top)
Image credit: Fabio Pastori

Gorgosaurus was discovered a little less than a decade after Albertosaurus, again, in Alberta. Gorgosaurus follows the same body structure of other tyrannosaurids, though the eye sockets are rounder on Gorgosaurus than that of other tyrannosaurids. Like its larger contemporary cousin, Gorgosaurus is extremely well-studied, with multiple specimens having been found. Skin impressions belonging to Gorgosaurus show a texture like that of modern birds. Although no evidence of feathers have been found, it is assumed that Gorgosaurus was covered in plumage in at least one growth stage. 

Gorgosaurus did not live a happy life. Many specimens are adorned with injuries such as infections and fractures. A pathological study on Gorgosaurus specimen TMP94.12.602 reveals a fracture in the right fibula's shaft, as well as rib fractures and bite lesions on the skull. All the wounds were shown to be healing.

Image credit: Natural History Museum of London

It's been long debated whether or not Gorgosaurus can be considered the same genus as Albertosaurus. Before, it was commonly accepted to lump the two into the same genus, though more recent studies show otherwise. Skull anatomy of Albertosaurus is more similar to that of Daspletosaurus, another contemporary tyrannosaurid, and Tyrannosaurus than it is to Gorgosaurus. Albertosaurus also has proportionately smaller fore limbs. To quote Dr. Currie, "[Albertosaurus and Gorgosaurus] were no more similar than Daspletosaurus and Tyrannosaurus [were]." For now, unless new research pops up, Albertosaurus and Gorgosaurus can be regarded as different genera.

The tropical ecosystem of Cretaceous Alberta was teeming with life. Albertosaurus and Gorgosaurus not only lived alongside each other, but as well as a another tyrannosaurid, Daspletosaurus. The more slender build of Albertosaurus and Gorgosaurus suggests that they were better suited to hunting hadrosaurids, while Daspletosaurus tackled armored prey. Hadrosaurids such as Parasaurolophus, Lambeosaurus, and Corythosaurus were most certainly abundant during the time. With the disappearance of most sauropods, the "duck-billed" dinosaurs had relatively low competition for food. Ceratopsians, the horned dinosaurs, were another relatively common dinosaur at the time. Pachyrhinosaurus, Chasmosaurus, Spinops, and Styracosaurus were some, but not all, of the ceratopsians to have lived with the tyrannosaurs. Among them were ankylosaurs such as Euoplocephalus, filling in an ecological niche the stegosaurs of the Jurassic Period left behind. Smaller predators like the ornithomimosaur Struthiomimus and the dromaeosaur Dromaeosaurus hunted smaller prey. Champsosaurus, a relative of the modern-day gharial, populated lakes and rivers. Overall, a lush and tropical climate allowed for an extremely diverse ecosystem of many different organisms.

Gorgosaurus libratus -  Called the 'opisthotonic' pose, caused by contraction of neck muscles during/after death
Photo by the author

References/Further Reading

"Royal Tyrrell Museum." Royal Tyrrell Museum. N.p., n.d. Web. 18 Aug. 2015.

Mccord, Robert. "Arizona Museum of Natural History." Arizona Museum of Natural History. N.p., n.d. Web. 18 Aug. 2015.

Switek, Brian, and Julius Csotonyi. Prehistoric Predators. N.p.: n.p., n.d. Print.

Palmer, Douglas, Simon Lamb, Angeles Gavira Guerrero, and Peter Frances. Prehistoric Life:. New York, NY: DK Pub., 2009. Print.

Benton, M. J. Walking with Dinosaurs: Fascinating Facts. New York: Dorling Kindersley Pub., 2000. Print.

Pim, Keiron. Dinosaurs the Grand Tour: Everything worth Knowing about Dinosaurs from Aardonyx to Zuniceratops. N.p.: n.p., n.d. Print.

Paul, Gregory S. Predatory Dinosaurs of the World: A Complete Illustrated Guide. New York: Simon and Schuster, 1988. Print.

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