Piatnitzkysaurids were among the first large theropods present in South America, and are evidence for a radiation of basal tetanurans in the middle Jurassic.[1] Although there is support for basal megalosauroid affinities, piatnitzkysaurids also share some traits with allosaurids, such as a 'sigmoidal' humerus.[citation needed]
If piatnitzkysaurids are megalosauroids, they can be distinguished from other megalosauroids due to the following synapomorphies (distinguishing features):[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 Condorraptor could be better interpreted as the result of individual variation within the species and not a separate taxon. The main noted differences between the two species 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 its remains, this placement is considered uncertain. Other studies have considered Xuanhanosaurus a basal tetanuran.[1] This taxon is still sometimes found as a piatnitzkysaurid.[5]
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:[6]
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