Albertosaurus sarcophagus

Osborn 1905

Evidence: Well over two dozen partial skulls and skeletons.

Campanian to Maastrichtian

Horseshoe Canyon, Judith River, and Lance Formations

Alberta; Canada: Montana, Wyoming; USA

Biology: 10 meters long – 3 tonnes

Albertosaurus were apparently found in large groups for at least part of their lives. A quarry at Dry Island, Alberta has produced more than two-dozen skeletons of a great variety of ages (Erickson et al.2006). Because all the individuals in the bone bed are over two years old, Erickson et al. hypothesized that there was an extremely high mortality rate before they reached that age. The range of growth stages at Dry Island has enabled a detailed comparison of juveniles with adults. It seems that, among tyrannosaurids, Albertosaurus sarcophagus was one of the more slow-growing species with only a slightly greater growth spurt during adolescence than Gorgosaurus libratus (Erickson et al. 2004). Although it is evident that all the individuals in the quarry belong to the same species, there is an immense amount of variation, especially in the teeth (Buckley et al. 2010). Currie (1998) believed that this aggregation represented social behaviour in Albertosaurusbut other authors have suggested that the presence of their impending doom, such as a flood, was the primary reason so many animals are found together (Roach et Brinkman 2007). It was probably a combination of both factors. Albertosaurus sarcophagus lived a relatively active life that involved interspecific fighting. Some Albertosaurus may have suffered infection from biting one another (Wolff et al. 2009) while most had bone abrasions and breaks as well as tendon pathologies (Bell 2010). These battle scars are evidence that albertosaurs were very social, albeit, not very amiable. The presence of a single very large individual at Dry Island may represent an alpha or senior member of a pack. It is the oldest Albertosaurus known to date at 28 years and 10 meters (Erickson et al. 2006). Because tyrannosaurids grow throughout their lives, giants like this one are possible. The average size of an adult Albertosaurus is closer to 8 meters and 2.5 tonnes (Paul 2010).

Interestingly, the Horseshoe Canyon Formation, were Albertosaurus sarcophagus are primarily found, is also home to Daspletosaurus, another large tyrannosaurid. There has been a lot of speculation over the relationship between these two apex predators since each must have assumed a unique ecological niche. Perhaps the more gracile Albertosaurus pursued faster hadrosaurs and the heavier Daspletosaurus preyed primarily on ceratopsians. In any case, Daspletosaurus ate young hadrosaurs at least some of the time (Varricchio 2001). In all likelihood, both animals probably hunted similar prey and competed violently with one another, just as leopards and lions do in Africa today. The Horseshoe Canyon is unique in its encompassment of Campanian and Maastrichtian fauna. While lambeosaurines are more common in Campanian strata and edmontosaurines in the Maastritchtian, both are present in the Horseshoe Canyon. Perhaps this explains, in part, the coexistence of Daspletosaurus and Albertosaurus in the same ecosystem.

Evolution

A very well known dinosaur, Albertosaurus sarcophagus is the iconic species of its genus and among the best known in its family, the Tyrannosauridae. There is no debate over its placement although the very similar Gorgosaurus libratus is sometimes included in the genus. Among non-Albertosaurinae tyrannosaurids, Daspletosaurus is most similar to A. sarcophagus, as the most basal member of the Tyrannosaurinae (Fiorillo et Tykoski 2014), though an unnamed species of tyrannosaurine from the Dinosaur Park Formation may be even more basal (Loewen et al. 2013). Gorgosaurus may be slightly more basal than A. sarcophagus in the Albertosaurinae.

References:

Bell, P. R. 2010. “Palaeopathological changes in a population of Albertosaurus sarcophagus from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada.” Canadian Journal of Earth Sciences 47: 1263-1268.

Buckley, L. G., D. W. Larson, M. Reichel, et T. Samman. 2010. “Quantifying tooth variation within a single population of Albertosaurus sarcophagus(Theropoda: Tyrannosauridae) and implications for identifying isolated teeth of tyrannosaurids.” Canadian Journal of Earth Sciences 47: 1227-1251.

Currie, P. J. 1998. “Possible evidence of gregarious behavior in tyrannosaurids.” Gaia 15: 271-277.

Erickson, G. M., P. J. Makovicky, P. J. Currie, M. A. Norell, S. A. Yerby, et C. A. Brochu. 2004. “Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs.” Nature 430: 772-775.

Erickson, G. M., P. J. Currie, B. D. Inouye, et A. A. Winn. 2006. “Tyrannosaur Life Tables: An Example of Nonavian Dinosaur Population Biology.” Science 313: 213-217.

Fiorillo, A. R. et R. S. Tykoski. 2014. “A Diminutive New Tyrannosaur from the Top of the World.” PLoS ONE 9(3): e91287.

Loewen, M. A., R. B. Irmis, J. J. W. Sertich, P. J. Currie, et S. D. Sampson. 2013. “Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans.” PLoS ONE 8(11): e79420.

Paul, G. S. 2010. The Princeton Field Guide to Dinosaurs. Princeton, NJ: Princeton University Press.

Roach, B. T., et D. L. Brinkman. 2007. “A Reevaluation of Cooperative Pack Hunting and Gregariousness in Deinonychus antirrhopus and Other Nonavian Theropod Dinosaurs.” Bulletin of the Peabody Museum of Natural History 48(1): 103-138.

Varricchio, D. J. 2001. “Gut contents from a Cretaceous tyrannosaurid: implications for theropod dinosaur digestive tracts.” Journal of Paleontology 75(2): 401-406.

Wolff, E. D. S., S. W. Salisbury, J. R. Horner, D. J. Varricchio. 2009. “Common Avian Infection Plagued the Tyrant Dinosaurs.” PLoS ONE 4(9): e7288.