Magnosaurus is a genus of tetanuran theropod dinosaur from the Middle Jurassic Period of England. It was named in 1923 by Friedrich von Huene from a partial skeleton found in Sherborne, in Dorset, England. Magnosaurus is often mixed up with the similarly named Megalosaurus. Huene did, however, interpret it as a more primitive species of Megalosaurus. Two species are known (M. lydekkeri and M. woodwardi).

M. lydekkeri
was first described in 1888 from a specimen recovered in the Lower Lias (Jurassic). It was given its proper status in 1926. A second species, M. woodwardi, was originally referred to as Sarcosaurus andrewsi.

Based on little remains recovered, little is known about the life and behavior of this dinosaur. It would have most likely been a bipedal carnivore of moderate size. It would have most likely been similar in appearance to the Eustreptospondylus, Dubreuillosaurus, and Afrovenator. It is estimated to have weighed about 385 pounds and maybe reached about 13 feet in length. These reports are based on sizes of other similar theropods.

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