Piatnitzkysauridae

So far, all known piatnitzkysaurids have only been found in Jurassic deposits of the western hemisphere/New world (however, if Xuanhanosaurus is included, this may expand their range). Piatnitzkysaurus and Condorraptor hail from the Cañadón Asfalto Formation of Argentina, which has been dated from the Toarcian epoch of the Early Jurassic to the Bathonian epoch of the Middle Jurassic (approximately 179 to 168 million years ago). Marshosaurus was found in the Morrison Formation of the United States, which was dated to the Kimmeridgian epoch of the Late Jurassic. Piatnitzkysaurids were among the first large theropods present in South America, and are evidence for a radiation of basal tetanurans in the middle Jurassic. In addition, this family shows several reversals to basal Tetanuran traits. These include: • 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==

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. 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. 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: }} }} In their 2025 description of the metriacanthosaurid Yuanmouraptor, Zou et al. recovered Piatnitzkysauridae as the sister taxon to Avetheropoda. These results are displayed in the cladogram below. ==References==