Metriacanthosauridae

Metriacanthosauridae, whose name means "moderately-spined lizards," were a family of allosauroid theropod dinosaurs that roamed Europe and Asia from the Middle Jurassic into the Early Cretaceous. They belong to the carnosaur group within the superfamily Allosauroidea. The family splits into two branches: Metriacanthosaurinae, the group containing dinosaurs most closely related to *Metriacanthosaurus*, and a second group made up of the close relatives of *Yangchuanosaurus*. These dinosaurs varied widely in body size, but their most distinctive physical feature was their neural spines. Most fossils come from Asia, though *Metriacanthosaurus* itself is European. The name Metriacanthosauridae takes priority over Sinraptoridae, which is considered a junior synonym.

Several clear skeletal traits set them apart from other allosauroids. The front branch of the maxilla was short or missing, a feature also seen in carcharodontosaurids and piatnitzkysaurids. The laterosphenoid bone connected to both the frontal and postorbital bones. The squamosal lacked a constriction at the lower temporal fenestra, a trait shared with megalosauroids, and it had a flange that covered the quadrate head from the side. A well-defined groove ran along the outer side of the dentary, holding a row of nerve and blood vessel openings. The axis vertebra had a broad, well-developed lamina between the spine and the rear joint processes. The hand was shorter than the lower arm. The middle tail vertebrae had neural spines that were rectangular and sheet-like. The hand lacked a fifth digit and the finger bones of the fourth digit, a condition also found in neovenatorids. The paired shafts of the ilium had a heart-shaped cross section, like those of coelophysids. The lower end of the ischium was fused, as in neovenatorids and basal tetanurans. In the teeth, the labial surface of the crown was flattened in lateral teeth, with the surface texture irregular and unoriented.

Within Metriacanthosauridae, the Metriacanthosaurinae subgroup had additional shared traits. The front-lower border of the maxillary antorbital fenestra was marked by a raised ridge, also seen in *Eoraptor*, coelophysids, *Masiakasaurus*, *Marshosaurus*, and *Compsognathus*.