Albertosaurus (; meaning " Alberta lizard ") is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, about 70 million years ago.

In 2009, researchers hypothesized that smooth-edged holes found in the fossil jaws of tyrannosaurid dinosaurs such as Albertosaurus were caused by a parasite similar to Trichomonas gallinae which infects birds.

An additional tyrannosaurid, Raptorex, was initially described as a more primitive tyrannosauroid, but likely represents a juvenile tyrannosaurine similar to Tarbosaurus.

While very large by the standard of modern predators, Daspletosaurus was not the largest tyrannosaurid.

The eye socket was circular rather than oval or keyhole-shaped as in other tyrannosaurid genera.

Parasaurolophus walkeri, from the Dinosaur Park Formation, was a member of a diverse and well-documented fauna of prehistoric animals, including well-known dinosaurs such as the horned Centrosaurus and Chasmosaurus ; fellow duckbills Gryposaurus and Corythosaurus ; tyrannosaurid Gorgosaurus ; and armored Edmontonia, Euoplocephalus and Dyoplosaurus.

In some areas, Daspletosaurus coexisted with another tyrannosaurid, Gorgosaurus, though there is some evidence of niche differentiation between the two.

In some areas, Gorgosaurus coexisted with another tyrannosaurid, Daspletosaurus.

Some of these bones contained bite marks made by the contemporary tyrannosaurid species Tarbosaurus bataar, and showed evidence consistent with scavenging.

Gorgosaurus is the best-represented tyrannosaurid in the fossil record, known from dozens of specimens.

Resembling a large tyrannosaurid, he can dish out the most damage of all the dino-beasts, but he's also the slowest.

The last and largest of the Parasaurolophus species, P. tubicen, lived in New Mexico alongside the large sauropod Alamosaurus, duckbill Kritosaurus, horned Pentaceratops, armored Nodocephalosaurus, Saurornitholestes, and the tyrannosaurid Bistahieversor.

However, tyrannosaurid forelimbs were extremely small for their body size and retained only two digits.

Daspletosaurus ( ; meaning " frightful lizard ") is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period.

In contrast, the forelimbs were extremely small and bore only two digits, although Daspletosaurus had the longest forelimbs in proportion to body size of any tyrannosaurid.

* Replica skeletons of Triceratops and Jane, a juvenile tyrannosaurid.

Lesions found in the fossil jaws of tyrannosaurid dinosaurs such as Tyrannosaurus rex were likely caused by a parasite similar to Trichomonas gallinae.

" Di ", " emperor ", refers to the relationship of this animal to Tyrannosaurus rex, the " king " tyrannosaurid.

Gorgosaurus ( ; meaning " fierce lizard ") is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76. 5 and 75 million years ago.

Diablo resembles a tyrannosaurid.

Large, predatory spinosaurids and allosaurids flourished during the Late Jurassic and Early Cretaceous, especially in Gondwana, but seem to have died out before the end of the Cretaceous, possibly due to competition from abelisaurid ceratosaurs and tyrannosaurid coelurosaurs.

In the Two Medicine Formation, Maiasaura lived alongside the tyrannosaurid Daspletosaurus, the oviraptorosaurian Chirostenotes, the troodontid Troodon, the dromaeosaurids Bambiraptor and Saurornitholestes, the enantiornithe bird Avisaurus, the nodosaurid Edmontonia, the ankylosaurid Euoplocephalus, the ceratopsids Achelousaurus, Brachyceratops, Einiosaurus, and Styracosaurus ovatus, the hypsilophodont Orodromeus, and the hadrosaurids Hypacrosaurus stebingeri and Prosaurolophus.

Dinosaurs that lived alongside Einiosaurus include the basal ornithopod Orodromeus, hadrosaurids ( such as Hypacrosaurus, Maiasaura, and Prosaurolophus ), the ankylosaurs Edmontonia and Euoplocephalus, the tyrannosaurid Daspletosaurus ( which appears to have been a specialist of preying on ceratopsians ), as well as the smaller theropods Bambiraptor, Chirostenotes, Troodon, and Avisaurus.

A tyrannosaurid attacking a P. cyrtocristatus.

Although relatively large for a theropod, Albertosaurus was much smaller than its more famous relative Tyrannosaurus, probably weighing less than 2 metric tons.

Albertosaurus was smaller than some other tyrannosaurids, such as Tarbosaurus and Tyrannosaurus.

Typically for a theropod, Albertosaurus was bipedal and balanced the heavy head and torso with a long tail.

The massive skull of Albertosaurus, perched on a short, S-shaped neck, was approximately 1 metre ( 3. 3 ft ) long in the largest adults.

The bite force of Albertosaurus was less formidable however, the maximum force, by the hind teeth, reaching 3413 Newton.

In 2010, the health of the Dry Island Albertosaurus assembly was reported upon.

Gorgosaurus was most closely related to Albertosaurus, and more distantly related to the larger Tyrannosaurus.

Gorgosaurus was smaller than Tyrannosaurus or Tarbosaurus, closer in size to Albertosaurus and Daspletosaurus.

Juveniles may also have had different lifestyles than adults, filling predator niches between the enormous adults and the smaller contemporaneous theropods, the largest of which were two orders of magnitude smaller than adult Albertosaurus in mass.

Since the first discovery in 1884, fossils of more than thirty individuals have been recovered, providing scientists with a more detailed knowledge of Albertosaurus anatomy than is available for most other tyrannosaurids.

Albertosaurus with a human for scale

Unlike most theropods, Albertosaurus and other tyrannosaurids were heterodont, with teeth of different forms depending on their position in the mouth.

Like with Tyrannosaurus, the maxillary ( cheek ) teeth of Albertosaurus were adapted in general form to resist lateral forces exerted by a struggling prey.

Two of the five Albertosaurus sarcophagus specimens with humeri in 1970 were reported by Dale Russel as having pathological damage to them.

Intermingled with the Albertosaurus remains of the Dry Island bonebed, the bones of the small theropod Albertonykus were found.

Adult Albertosaurus were the apex predators in this environment, with intermediate niches possibly filled by juvenile albertosaurs.

J. B. Joseph Tyrrell, a geologist and cartographer whose exploits include the discovery of Albertosaurus bones in Alberta's Bandlands, and making first contact with the Ihalmiut (" People from Beyond ") of the Keewatin district of Canada's Northwest Territories, served as founding Honorary President.