Piatnitzkysauridae
Extinct family of megalosauroid or basal allosauroid dinosaurs.
Piatnitzkysauridae is an extinct family of dinosaurs, classified as either megalosauroids or basal allosauroids. The family includes three or four known genera: *Condorraptor*, *Marshosaurus*, *Piatnitzkysaurus*, and possibly *Xuanhanosaurus*. The most complete and best-studied member is *Piatnitzkysaurus*, which also lends its name to the group.
All confirmed piatnitzkysaurid fossils come from Jurassic deposits in the Western Hemisphere. *Piatnitzkysaurus* and *Condorraptor* were found in Argentina’s Cañadón Asfalto Formation, which dates primarily to the Middle Jurassic (Aalenian to Bathonian, approximately 174 to 168 million years ago). *Marshosaurus* comes from the Morrison Formation in the United States, which dates to the Kimmeridgian (Late Jurassic). If *Xuanhanosaurus* belongs to this family, the group’s range would extend to Asia.
These dinosaurs were among the first large theropods in South America and suggest a radiation of basal tetanurans during the Middle Jurassic. While evidence supports a basal megalosauroid classification, piatnitzkysaurids also share certain traits with allosaurids, such as a sigmoidal (S-shaped) humerus.
If piatnitzkysaurids are megalosauroids, they can be distinguished from other members of that group by several unique features. These include nutrient foramina on the maxilla arranged in two parallel rows (also seen in *Eocarcharia* and *Shaochilong*); vertically striated or ridged paradental plates (also in Abelisauridae, *Megalosaurus*, and *Proceratosaurus*); reduced parapophyses on the axis (also in Coelophysoidea, *Eustreptospondylus*, and *Afrovenator*); anteriorly inclined posterior dorsal neural spines (paralleling Allosauroidea); and a humerus with a canted (forward-bent) distal condyle (also in *Dilophosaurus*, *Poekilopleuron*, Allosauridae, and *Fukuiraptor*), often described as sigmoidal.
The family also shows reversals to basal tetanuran traits, including a short or absent anterior process of the maxilla (also in Metriacanthosauridae and Carcharodontosauridae), moderately developed diapophyses on the axis, and no pleurocoels on the axis.
Piatnitzkysauridae is defined as all megalosauroids more closely related to *Piatnitzkysaurus* than to either *Spinosaurus* or *Megalosaurus*.
Quick Facts
- Taxon
- Piatnitzkysauridae
- Type Species
- Piatnitzkysaurus floresi
- Type Species Authority
- Bonaparte, 1979
Facts from the source article.
Lore & Background
All known piatnitzkysaurids have been found in Jurassic deposits of the western hemisphere, though inclusion of Xuanhanosaurus may expand their range to Asia. Piatnitzkysaurus and Condorraptor come from the Cañadón Asfalto Formation of Argentina, dated to the Middle Jurassic (Aalenian to Bathonian epochs, approximately 174 to 168 million years ago). Marshosaurus was found in the Morrison Formation of the United States, dated to the Kimmeridgian epoch of the Late Jurassic. The family shares some traits with allosaurids, such as a sigmoidal humerus.
Reader's Guide
Piatnitzkysauridae was defined by Carrano et al. in 2012 as all members of Megalosauroidea more closely related to Piatnitzkysaurus than to Spinosaurus or Megalosaurus. The clade was first recognized by Benson in 2010 during a redescription of Megalosaurus. Piatnitzkysauridae has been recovered as the sister taxon to Megalosauria, a clade containing megalosaurids and spinosaurids. Within the family, Condorraptor and Piatnitzkysaurus are generally grouped together, excluding Marshosaurus, due to shared features such as flat anterior faces of presacral vertebrae and a pronounced ventral keel on anterior dorsal vertebrae. Some researchers suggest Condorraptor may represent individual variation within Piatnitzkysaurus rather than a separate taxon. Xuanhanosaurus was placed as a sister taxon in 2010 but its affinities remain uncertain due to incomplete remains. In 2019, Rauhut and Pol described Asfaltovenator vialidadi and found Piatnitzkysauridae to fall within Allosauroidea. In 2025, Zou et al. recovered Piatnitzkysauridae as the sister taxon to Avetheropoda.
Did You Know?
- Piatnitzkysauridae consists of three to four known genera: Condorraptor, Marshosaurus, Piatnitzkysaurus, and possibly Xuanhanosaurus.
- Piatnitzkysaurus and Condorraptor both come from the Cañadón Asfalto Formation of Argentina, dated from the Toarcian to Bathonian epochs.
- Piatnitzkysaurids share a sigmoidal humerus with allosaurids.
- The family was defined by Carrano et al. in 2012 and first recognized as a clade by Benson in 2010.
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