Piatnitzkysaurus (/ˌpiːətnɪtskiːˈsɔːrəs/ pee-ət-NITS-kee-SOR-əs; meaning "Piatnitzky's lizard") is a genus of tetanuran theropod dinosaur that lived approximately 179 to 177 million years ago during the lower part of the Jurassic Period in what is now Argentina.

The holotype specimen of Piatnitzkysaurus, PVL 4073, was collected during expeditions in 1977, 1982, and 1983 at the Cañadón Asfalto Formation in sediments that were deposited during the Middle-Late Toarcian stage of the Jurassic period, approximately 179 to 177 million years ago.

[2] In Bonaparte’s 1979 paper on the taxon, he briefly described it along with the sauropods Patagosaurus fariasi (a cetiosaurid)and Volkheimeria chubutensis (an early eusauropod) from the same deposits.

Piatnitzkysaurus was a relatively lightly built medium-sized bipedal carnivore that was around 4.3 metres (14 ft) long and around 450 kilograms (990 lb) in mass, though such estimates apply to the holotype, which is a subadult.

The relative lengths of the ulna in respect to the humerus and femur are also similar to those of basal theropods, which means the forelimbs of Piatnitzkysaurus are proportionally longer than in Allosaurus.

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.

Given the distant phylogenetic position of the basal tetanuran Piatnitzkysaurus and the advanced maniraptoran and deinonychosaurian taxa Sinovenator and Sinornithosaurus, the presence of this recess represents a convergence and can be considered an autapomorphy of the former genus.