Allosaurus: The Different Lizard

Allosaurus has always been one of my favorite dinosaurs. There is just something appealing about this large carnivorous dinosaur.

Allosaurus was a large, bipedal theropod carnivorous dinosaur that lived during the late Jurassic Period (195 tp 140 million years ago). It was a member of the Saurischian ("lizard hipped") group of dinosaurs. (Be sure to read my article "Dinosaur Primer" for more information about how dinosaurs are classified.) It was named by Charles Othniel Marsh in 1883; he gave it the name Allosaurus (meaning "different lizard") because the appearance of its vertebrae was very different from that of any other dinosaur known during the early history of paleontology.

Allosaurus was for a long time classified in the Infraorder Carnosauria ("flesh lizards") of which Tyrannosaurus, Tarbosaurus, Ceratosaurus, and Dilophosaurus were also members. Many paleontologists, however, have dropped this Infraorder from their classification systems, and simply classify the former Carnosaurs into their respective Families.

Allosaurus is a member of the Family Allosauridae, which includes Carcharodontosaurus, Acrocanthosaurus, Giganotosaurus, and Yangchuanosaurus.

The naming of Allosaurus has a rather confusing history. A tail bone of Allosaurus was first discovered in 1869 in Grand County, Colorado by Dr. Ferdinand Hayden. This tail bone was described in 1870 by Joseph Leidy, who named the dinosaur Poicilopleurodon (meaning "varying cavity"), after a European genus of dinosaur. Leidy later renamed the dinosaur Antrodemus. In 1877, one of O. C. Marsh's field assistants discovered the partial skeleton of a large carnivorous dinosaur in Fremont County, Colorado; Marsh named this skeleton Allosaurus. Marsh then abandoned the quarry in Fremont County, and returned to Wyoming where he was having better luck finding dinosaur skeletons. In 1883, another one of Marsh's assistants returned to the Fremont County quarry, and excavated an almost complete skeleton of Allosaurus, as well as several partial skeletons. Despite the fact that Leidy's name of Antrodemus took precedence over the name Allosaurus, and in 1920 Charles Gilmore of the Smithsonian Institution in Washington D. C. actually described Marsh's skeletons as Antrodemus, the genus name Allosaurus is the one that is recognized today, and is based on the 1883 skeleton.

Allosaurus has a large but surprisingly lightly constructed skull with long, curved, serrated teeth. These teeth would have been used to tear off large chunks of meat. Allosaurus was heavy and powerful, and not built for high-speed pursuits of its prey. It is believed to have preyed on some of the larger ornithischian herbivores that lived at the same time, such as Comptosaurus and Stegosaurus, and perhaps even the sauropods Diplodocus and Apatosaurus.

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