Metriacanthosauridae

Diagnostic traits

Metriacanthosaurids share the following unambiguous synapomorphies among allosauroids:

• A short or absent anterior ramus of the maxilla (also found in carcharodontosaurids and piatnitzkysaurids).

• The laterosphenoid articulated on the frontal and postorbital.

• A squamosal without constriction of the lower temporal fenestra. (also found in megalosauroids)

• 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 (also found in neovenatorids).

• A heart-shaped cross section of the ilium's paired midshafts (also found in coelophysids).

• Fused distal end of the ischium (also found in neovenatorids and basal tetanurans). Metriacanthosaurids share the following dental synapomorphies among theropods:

• surface centrally positioned on the labial surface of the crown roughly flattened in lateral teeth

• irregular and non-oriented enamel surface texture

Metriacanthosaurines share the following synapomorphies among metriacanthosaurids:

• The anteroventral border of the maxillary antorbital fenestra being demarcated by a raised ridge (also found in Eoraptor, coelophysids, Masiakasaurus, Marshosaurus, and Compsognathus).
• A pronounced ventral keel on the anterior dorsal vertebrae (also found in Condorraptor, Piatnitzkysaurus, Carcharodontosaurus and many megalosaurians).
• 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 (also found in coelophysids, Eustreptospondylus, Afrovenator, Megalosaurus and Compsognathus).
• A bulbous fibular crest on the tibia (also found in Sinosaurus).

Classification

Carrano, Benson & Sampson (2012) noted that the name Metriacanthosauridae should be used as it has priority over Sinraptoridae.

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.

Palaeobiogeography

Metriacanthosauridae fossils have only been found in modern Europe and Asia, parts of the prehistoric landmass Laurasia. The biogeographic origin of metriacanthosaurids based on phylogenetic analysis is suggested to be South-East Asia, specified as "Chinese provinces of Sichuan and Yunnan and areas south of this", and the earliest known taxa are Shidaisaurus from southern China and Alpkarakush from Kyrgyzstan. Fragmentary remains of allosauroids from the late Middle-early Late Jurassic Marnes de Dives in northern France bear close similarities to metriocanthosaurids, and may belong to members of the group.

References

References

1. (2019). "Probable basal allosauroid from the early Middle Jurassic Cañadón Asfalto Formation of Argentina highlights phylogenetic uncertainty in tetanuran theropod dinosaurs". Scientific Reports.
2. (2012). "The phylogeny of Tetanurae (Dinosauria: Theropoda)". Journal of Systematic Palaeontology.
3. Bailey, Jack Bowman. "Neural Spine Elongation in Dinosaurs: Sailbacks or Buffalo-Backs?" Journal of Paleontology, vol. 71, no. 06, 1997, pp. 1124–1146., doi:10.1017/s0022336000036076.
4. (24 November 2019). "The distribution of dental features in non-avian theropod dinosaurs: Taxonomic potential, degree of homoplasy, and major evolutionary trends". Palaeontologia Electronica.
5. Sereno, Paul. "Sinraptoridae". Taxon Search.
6. Benson, R.B.J., Carrano, M.T and Brusatte, S.L.. (2010). "A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic". Naturwissenschaften.
7. (1 August 2024). "A new theropod dinosaur from the Callovian Balabansai Formation of Kyrgyzstan". [[Zoological Journal of the Linnean Society]].
8. (24 March 2022). "New data on the theropod diversity from the Middle to Late Jurassic of the Vaches Noires cliffs (Normandy, France)". Geodiversitas.