Piatnitzkysauridae

Piatnitzkysauridae is an extinct family of megalosauroid dinosaurs. It only consists of three known dinosaur genera: Condorraptor, Marshosaurus, and Piatnitzkysaurus. The most complete and well known member of this family is Piatnitzkysaurus, which also gives the family its name.[1]

Piatnitzkysaurids Temporal range: Middle - Late Jurassic, 170.3–152 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Piatnitzkysaurus, type genus of the Piatnitzkysauridae
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Infraorder:	†Carnosauria (?)
Family:	†Piatnitzkysauridae Carrano, Benson & Sampson, 2012
Type species
†Piatnitzkysaurus floresi Bonaparte, 1979
Genera
†Condorraptor †Marshosaurus †Piatnitzkysaurus

Description

A skull of Marshosaurus showing the maxilla

So far all known piatnitzkysaurids have only been found in Jurassic deposits of the western hemisphere.[2] Piatnitzkysaurus and Condorraptor hail from the Cañadón Asfalto Formation of Argentina, which has been dated to the Middle Jurassic (approximately 165 million years ago). Marshosaurus was found in the Morrison Formation of the United States, which was dated to the Late Jurassic.

Piatnitzkysaurids were among the first large theropods present in South America, and are evidence for a radiation of megalosauroids and other tetanurans in the middle Jurassic.[1] Although there is strong support for their megalosauroid affinities, piatnitzkysaurids also share some traits with allosaurids, such as a 'sigmoidal' humerus.

Piatnitzkysaurids can be distinguished from other megalosauroids due to the following synapomorphies (distinguishing features):[1]

• Nutrient foramina on the surface of the maxilla which are arranged in two parallel rows (also found in Eocarcharia and Shaochilong).
• Vertically striated or ridged paradental plates (also found in Abelisauridae, Megalosaurus and Proceratosaurus).
• Reduced parapophyses on the axis (also found in Coelophysoidea, Eustreptospondylus and Afrovenator).
• Anteriorly inclined posterior dorsal neural spines (in parallel with Allosauroidea).
• A humerus with a canted (bent forward, away from the body) distal condyle (also in Dilophosaurus, Poekilopleuron, Allosauridae and Fukuiraptor). This form has also been described as 'sigmoidal' (S-shaped).[3]

In addition, this family shows several reversals to basal Tetanuran traits. These include:[1]

• A short or absent anterior process of the maxilla (also in Metriacanthosauridae and Carcharodontosauridae).
• Moderately developed (rather than reduced or absent) diapophyses on the axis.
• No pleurocoels on the axis.

Classification

Life restoration of Piatnitzkysaurus

Piatnitzkysauridae is defined as all members of Megalosauroidea more closely related to Piatnitzkysaurus than to either Spinosaurus or Megalosaurus. Condorraptor, Marshosaurus, and Piatnitzkysaurus were all placed in a clade by Benson in 2010 during a redescription of Megalosaurus.[3] This clade was defined as a family by Carrano et al in 2012. Piatnitzkysauridae has been recovered as the sister taxa to Megalosauria, a clade containing the megalosaurids (such as Megalosaurus and Torvosaurus) and the spinosaurids (such as Spinosaurus and Baryonyx).[1]

Condorraptor and Piatnitzkysaurus are generally grouped together within this family in a clade excluding Marshosaurus. This is not only due to Condorraptor and Piatnitzkysaurus being from the same locality and time period, but also due to them having flat anterior faces of presacral vertebrae as well as a pronounced ventral keel on the anterior dorsal vertebrae.[1][3] Due to the strong resemblance to Piatnitzkysaurus, it has been suggested that the sister taxa Condorraptor could be better interpreted as the result of individual variation within the species, and not as separate taxa. The main noted differences between the two dinosaurs include both a less well developed enemial crest and a first sacral vertebra with a shallower fossa in Condorraptor.[4]

Xuanhanosaurus, a problematic tetanuran with uncertain affinities, was placed as the sister taxon of these three genera when their relation was first observed in 2010.[3] However, due to the incompleteness of Xuanhanosaurus's remains, this placement is considered uncertain. Other studies have considered Xuanhanosaurus a basal tetanuran.[1]

In 2019, Rauhut and Pol described Asfaltovenator vialidadi, a basal allosauroid displaying a mosaic of primitive and derived features seen within Tetanurae. Their phylogenetic analysis found traditional Megalosauroidea to represent a basal grade of carnosaurs, paraphyletic with respect to Allosauroidea. Because the authors amended the definition of Allosauroidea to include all theropods that are closer to Allosaurus fragilis than to either Megalosaurus bucklandii or Neornithes, the Piatnitzkysauridae was found to fall within Allosauroidea. A cladogram displaying the relationships they recovered is shown below:[5]

Carnosauria	Monolophosaurus       Spinosauridae       Megalosauridae   Allosauroidea   Xuanhanosaurus       Piatnitzkysauridae       Asfaltovenator       Metriacanthosauridae       Allosaurus     Carcharodontosauria

References

1. Carrano, M. T.; Benson, R. B. J.; Sampson, S. D. (2012). "The phylogeny of Tetanurae (Dinosauria: Theropoda)". Journal of Systematic Palaeontology. 10 (2): 211–300. doi:10.1080/14772019.2011.630927.
2. "Piatnitzkysauridae". Paleobiology Database. Retrieved 20 June 2013.
3. BENSON, ROGER B. J. (2010-04-01). "A description ofMegalosaurus bucklandii(Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods". Zoological Journal of the Linnean Society. 158 (4): 882–935. doi:10.1111/j.1096-3642.2009.00569.x. ISSN 0024-4082.
4. Novas, Fernando (2009). The Age of Dinosaurs in South America. Indiana University Press. p. 118. ISBN 0253352894.
5. Rauhut, Oliver W. M.; Pol, Diego (2019-12-11). "Probable basal allosauroid from the early Middle Jurassic Cañadón Asfalto Formation of Argentina highlights phylogenetic uncertainty in tetanuran theropod dinosaurs". Scientific Reports. 9 (1): 18826. doi:10.1038/s41598-019-53672-7. ISSN 2045-2322. PMC 6906444. PMID 31827108.