Allosaurus is an extinct genus of large theropod dinosaur that lived around 150 million years ago. Along with T-rex, it is arguably the most popular dinosaur in popular culture. This genus is known from more fossil remains than any other large, predatory dinosaurs. For more than half of the twentieth century, this genus was known as Antrodemus. Allosaurus fragilis is the best-known species of this genus.

History and Discovery

In the late nineteenth century, large scale of dinosaur fossil discovery resulted in bone wars. And, it led paleontologists to assign different genus and species names to Allosaurus specimens. The first fossil sample was allocated to the genus Poekilopleuron by Joseph Leidy. But later he changed his mind and assigned its own genus Antrodemus. The jeopardy was later corrected by other paleontologists; and Antrodemus, Creosaurus and Labrosaurus were assigned as synonyms for Allosaurus.

Allosaurus itself was described in 1877, based on YPM 1930 (the holotype specimen) by Othniel Charles Marsh. The holotype contained fragmentary bones including the shaft of the right humerus. This time, Marsh and fellow paleontologist Edward Drinker Cope, named several genera based on similarly sparse materials, such as Creosaurus and Labrosaurus described by Marsh, and Epanterias described by Cope.

Wyoming specimens nicknamed Big Al (MOR 693) and Big Al Two are two of the most popular Allosaurus specimens in paleontology circle. Big Al, around 95% complete, was unearthed in 1991. Big Al Two, which had the best-preserved skeleton impression to date, was found in 1996.

In 1999, Allosaurus fossil samples were reported from Portugal. Remains of this species were also found in Kimmeridgian-age rocks of Tendaguru, in Tanzania.

Physical Description

Allosaurus was a heavily built dinosaur like Tyrannosaurus. They had a large skull with ridges on the top of the head and above its eyes. It had powerful jaws with sharp, long, serrated teeth; and a strong, S-shaped neck. Allosaurus’ brain was more consistent with crocodilian brains rather than other living archosaurs. They had thin, fragile Gastralia attached to the skin in the belly region. It had small, three-fingered forearms with sharp claws; and large and powerful hind legs. They also possessed a long, heavily balanced tail.

Adaptation and Behavior

Allosaurus used to live on flat flood plains with distinct wet and dry seasons. They were on the top of the food chain. It coexisted with fellow large theropods like Torvosaurus and Ceratosaurus. Their prey included stegosaurids, sauropods and contemporaneous. Some theories suggested that they hunted in packs, and probably ambushed their prey. Recent researches were indicative of their scavenging behavior.

Etymology

The name “Allosaurus” has come from Greek words “allos” meaning ‘different’ or ‘other’, and “sauros” meaning ‘lizard.’ The name is thus as their vertebrae samples were different compared to other dinosaurs known at that time. The species name “fragilis” meaning ‘fragile’ refers to lightening characteristics in the vertebrae.

Interesting Facts

• The largest definitive Allosaurus fossil specimen (AMNH 680) was estimated at 9.7 meters in length.
• Histological analysis suggested that their lifespan was around 28 years.
• The weight of Allosaurus has been a matter of debate for years. Researchers, using subadult specimen Big Al as well as some computer modeling, came to the conclusion that their average weight was 3300 lbs.
• In the Morrison Formation, Allosaurus is commonly found in the same sites as Stegosaurus, Apatosaurus, Camarasaurus and Diplodocus.
• 38 museums in 8 countries had Allosaurus material or casts excavated from the Cleveland-Lloyd Dinosaur Quarry.
• Allosaurus is US state Utah’s official state fossil.
• Allosaurus has been depicted in several documentary films (e.g. BBC’s Walking with Dinosaurs, The Ballad of Big Al and Dinosaur Revolution), movies (e.g The Lost World, The Beast of Hollow Mountain, and The Valley of Gwangi), toy lines (Papo Allosaurus), computer games (Jurassic Park Builder), online games and books.