|Piatnitzkysaurus, type genus of the Piatnitzkysauridae|
Carrano, Benson & Sampson, 2012
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.
So far all known piatnitzkysaurids have only been found in Jurassic deposits of the western hemisphere. 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. Although there is strong support for their megalosauroid affinities, piatnitzkysaurids also share some traits with allosaurids, such as a 'sigmoidal' humerus.
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. 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).
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. 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.
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. However, due to the incompleteness of Xuanhanosaurus's remains, this placement is considered uncertain. Other studies have considered Xuanhanosaurus a basal tetanuran.
In 2019 saw the description and publication of Asfaltovenator vialidadi, a basal allosauroid that curiously has characteristics displaying primitive and derived features seen in Tetanurae. Their phylogenetic analysis has found Megalosauridae to be a basal grade of carnosaurs in respect to Allosauroidea.