Metriacanthosauridae
Metriacanthosauridae is an extinct family of allosauroid theropod dinosaurs that lived in Europe and Asia from the Middle Jurassic to the Early Cretaceous. The family is split into two subgroups: Metriacanthosaurinae, which includes dinosaurs closely related to Metriacanthosaurus, and another group composed of the close relatives of Yangchuanosaurus. Metriacanthosaurids are considered carnosaurs, belonging to the Allosauroidea superfamily. The group includes species of large range in body size. Of their physical traits, most notable are their neural spines. The records of the group are mostly confined to Asia, though Metriacanthosaurus is known from Europe. Metriacanthosauridae is used as a senior synonym of Sinraptoridae.
Diagnostic traits
Metriacanthosaurids share the following unambiguous synapomorphies among allosauroids:- A short or absent anterior ramus of the maxilla.
- The laterosphenoid articulated on the frontal and postorbital.
- A squamosal without constriction of the lower temporal fenestra.
- A flange on the squamosal covering the quadrate head laterally.
- A well-defined longitudinal groove on the lateral side of the dentary housing a row of neurovascular foramina.
- Broad, well developed spinopost-zygapophyseal lamina on the axis.
- A manus shorter than the forearm.
- Subrectangular and sheet-like neural spines of middle caudal vertebrae.
- A manus without digit V or the phalanges of digit IV.
- A heart-shaped cross section of the ilium's paired midshafts.
- Fused distal end of the ischium.
- surface centrally positioned on the labial surface of the crown roughly flattened in lateral teeth
- irregular and non-oriented enamel surface texture
- The anteroventral border of the maxillary antorbital fenestra being demarcated by a raised ridge.
- A pronounced ventral keel on the anterior dorsal vertebrae.
- A straight posterior margin of the iliac postacetabular process.
- The angle between the long axes of the pubic shaft and boot being less than 60 degrees.
- A ventrally curved ischial shaft.
- A bulbous fibular crest on the tibia.
Classification
Furthermore, the 2012 study named a new subfamily Metriacanthosaurinae to include all metriacanthosaurids more closely related to Metriacanthosaurus than to Yangchuanosaurus. A much larger phylogenetic analysis found Xuanhanosaurus, previously considered a basal megalosauroid, to be the basalmost metriacanthosaurid. Both Poekilopleuron and Lourinhanosaurus were recovered outside the family, and many taxa within the Metriacanthosauridae were in polytomy. However, the positions of Xuanhanosaurus and Poekilopleuron were very unstable, and their exclusion from the analysis gave a more resolved and stable cladogram. The cladogram presented here follows that study.