Albertosaurus sarcophagus al-BER-toh-SOR-us

"Alberta lizard"

Albertosaurus silhouette — silhouette · Ivan Iofrida (CC-BY) via PhyloPic

Length: 9 m (29.5 ft) — About 9 m long, ~2 tonnes — leaner and faster than T. rex.
Period: Late Cretaceous (73–70 Mya)
Place: North America · Alberta, Canada
Food: Carnivore — Hadrosaurs and ceratopsians; build suggests a more agile hunter than T. rex.
Clade: Tyrannosauridae Dinosauria Saurischia Theropoda Coelurosauria Tyrannosauroidea Late-Cretaceous tyrants: T. rex, Tarbosaurus, Albertosaurus.

A leaner Albertan cousin of T. rex, known from a bonebed that hints it hunted in groups.

Albertosaurus reconstruction by Connor Ashbridge — Reconstruction · Connor Ashbridge (CC-BY)

Albertosaurus was a tyrannosaur built for speed. It was smaller and lighter than Tyrannosaurus rex, with long legs suited to chasing prey across the floodplains of what is now Alberta. A famous bonebed in Dry Island contains at least 22 individuals of different ages, hinting that Albertosaurus may have lived in groups.

More about Albertosaurus

Discovery

Named by Henry Fairfield Osborn · 1905 · The type specimen, a partial skull, came from the Horseshoe Canyon Formation alongside the Red Deer River in Alberta, Canada.

A Geological Survey of Canada expedition led by geologist Joseph Burr Tyrrell collected the partial skull on June 9, 1884. Osborn later named the genus in 1905, in a one-page note appended to his description of Tyrannosaurus rex.

The name means "Alberta lizard." It pairs the Canadian province of Alberta with the Greek word sauros, meaning "lizard," the most common suffix in dinosaur names.

Henry Fairfield Osborn. He named Albertosaurus sarcophagus in 1905, in the same paper in which he described Tyrannosaurus rex.

Did Albertosaurus actually live and hunt in groups?

The discovery of 26 individuals at one site is described as evidence of gregarious behavior. That clustering hints these animals may have gathered or moved together, though the text presents it as evidence rather than settled proof.

For the curious → Was Albertosaurus scaly or feathered?

Two skin impressions are known, and both show scales: pebbly patches that grow larger and somewhat hexagonal, plus two larger feature scales set 4.5 cm apart. No feathers are preserved in these patches, so the direct fossil evidence so far points to scaly skin, at least on the belly.

What we know

Discovered in 1884 by Joseph B. Tyrrell — the museum in Alberta is named after him.
Smaller and more lightly built than T. rex, with longer leg bones relative to body.
Two-fingered hands like all later tyrannosaurs.
Lived 5–10 million years before T. rex, in the same general region.

What we guess

Whether the Dry Island bonebed represents a pack or just animals trapped together by a flood.
Adult speed estimates range from 20 to 30 km/h — debated based on bone strength.
Whether the smaller body meant chasing faster prey, or just less competition with bigger tyrannosaurs.