Albertosaurus

Credit: Gabriel Ugueto.

*Albertosaurus* is an extinct genus of tyrannosaurid that lived during the Late Cretaceous in Alberta.

## Description

Compared to other tyrannosaurs, *Albertosaurus* is quite small. *Albertosaurus* has a similar body plan to other tyrannosaurs, and had a heavy head and torso and a long, thick tail. *Albertosaurus* has two digits on it forelimbs, a feature many tyrannosaurs have, alongside the greatly reduced size of the arms. The two legs ended in four digits, three which reach the ground, and the fourth; the hallux, resting on the ankles. Albertosaurus may have relied on taking long strides, rather than sprinting, like it's Hell Creek relative, *Tyrannosaurus*. Scientists think *Albertosaurus* could have reached a maximum walking speed of about 21 kilometers/hour. The slowest walking speed of Albertosaurus has been placed at about 14 kilometers/hour.

As of today, two skin samples have been attributed to *Albertosaurus*; both underneath the torso, right below the gastralia. The scales resemble pebbles, eventually growing in size and appearing like hexagons. The specimens also preserve two feature scales, each measured to be placed about 4.5 centimeters away from one another. Another skin impression attributed to *Albertosaurus* is from an unknown region of the body. The scales are small, diamond-shaped, and arranged in tightly-packed rows.

## Paleoecology

*Albertosaurus* would have preyed on large dinosaurs such as *Edmontosaurus*. *Albertosaurus* was one of the apex predators in their habitat, but were preyed upon as juveniles by most other animals. *Albertosaurus* lived in Alberta, earning it's name.

## Paleobiology

### Life History

Using bone histology, scientists were able to determine the life history of many tyrannosaurids. Gregory Erikson and co. compared many juvenile, teenage, sub-adult and adult specimens to find an average growth-rate. *Albertosaurus* has the lowest growth history, however ends up at the same total body mass as *Gorgosaurus*. On the graph to the right, *Albertosaurus* is shown in red. The study concluded that tyrannosaurids underwent a rapid growth rate in their teens, and reach sexual maturity in their adult years.

### Social Behaviour

*Albertosaurus* remains found in small groups, including various adults and juveniles have been discovered in mass grave sites. Unlike predator traps like La Brea Tar Pits, the group died at the same time. Some interpret this as evidence for active pack behaviour, while others are skeptical the individuals were brought together by drought or food, or their corpses washed together in a flood. Some think that Albertosaurus flooded together at carcasses like komodo dragons, and some others think overly aggressive competition among animals leads to infighting and cannibalization. The stilt-like legs of *Albertosaurus*, and mostly juveniles, leads Philip J. Currie to speculate that *Albertosaurus* may have been some of the fastest dinosaurs, being faster than their prey in their juvenile stages to be able to support such vigorous growth.

Other active hypothesis say that juvenile *Albertosaurus* started their lives as small non-dominant carnivores, then grew into the apex predator niche. The fossil record preserving such behaviour is quite rare, making testing theories hard. Most still think the mass grave sites of *Albertosaurus* are caused by flood waters or other causes, but nothing can be definitively proven.

## Notable Specimens

* CMN 5600: A specimen measured at 9.7 meters (37 feet) long and 4 tonnes (4.4 short tons).

* TMP 1985 098 0001: A well preserved skull filled with matrix.

## Discovery

The first remains of *Albertosaurus* were recovered from the Horseshoe Canyon Formation in 1884. Initially they were named *Laelaps*. *Laelaps* was a genera of dinosaur named in 1866 and used on a variety of North American theropods including *Tyrannosaurus* itself. However this genus fell out of favour in the early 1900s as it was already used for a type of mite. In 1905 the *Laelaps* remains found at Horseshoe Canyon were renamed *Albertosaurus*. Since then, over thirty *Albertosaurus* skeletons have been found, making it one of the best known tyrannosaurs.

        When remains of another tyrannosaur from the Dinosaur Park Formation in 1913 were discovered, many scientists thought the new genus *Gorgosaurus* was a misidentified *Albertosaurus* skeleton assigned a distinct genus. Further research shows the two species were most closely related than to any other tyrannosaur. The situation has been compared to the ongoing *Daspletosaurus*-*Tyrannosaurus* distinction studies.

## Species

### Reassigned Species

* *"A." periculosus* (=juvenile tyrannosaurines, *Alioramus* or basal tyrannosauroids?, =*Tarbosaurus*?)

## Synonyms

### Genus Synonymy

* *Gorgosaurus*?
* *A. ("Nanotyrannus")*

### Species Synonymy

* *Deinodon sarcophagus*
* *A. arctunguis*
* *Deinodon arctunguis*
* *A. megagracilis*
* *"A." olseni*

## References

* https://en.wikipedia.org/wiki/Albertosaurus
* Paul, G. S., 1988, Predatory Dinosaurs of the World, a complete Illustrated guide: New York Academy of sciences book
* https://www.theropoddatabase.com/Tyrannosauroidea.html