Metriacanthosaurus (meaning "moderately-spined lizard") is a genus of sinraptorid dinosaur from the upper Oxford Clay of England, dating to the mid-Jurassic Period, about 160 million years ago (lower Oxfordian).
In 1923, German paleontologist Friedrich von Huene wrote a paper on Jurassic and Cretaceous European carnivorous dinosaurs. In this paper, he examined a specimen, OUM J.12144, including an incomplete hip, a leg bone, and part of a backbone, and believed it was a new species of Megalosaurus: Megalosaurus parkeri. The specific name honours W. Parker who in the nineteenth century had collected the fossils near Jordan's Cliff at Weymouth.
In 1932, however, von Huene concluded it was species of Altispinax, A. parkeri.
In 1964, scientist Alick Walker decided these fossils were too different from Altispinax, as it lacked the long vertebral spines, and named a new genus, Metriacanthosaurus. The generic name is derived from Greek metrikos, "moderate", and akantha, "spine". Metriacanthosaurus thus gets its name from its vertebrae, which are taller than typical carnosaurs, like Allosaurus, but lower than other high-spined dinosaurs like Acrocanthosaurus.
Metriacanthosaurus was a medium-sized theropod with a femur length of eighty centimetres. Gregory S. Paul in 1988 estimated its weight at a tonne.
Originally assigned by Walker to the Megalosauridae, Metriacanthosaurus has since been found to form a family with Yangchuanosaurus and other close relatives, named Metriacanthosauridae in 1988. Contrary to ICZN rules for naming animal groups, this family has been referred to mainly by the junior synonym Sinraptoridae.