Piatnitzkysaurus (meaning "Piatnitzky's lizard") is a genus of theropod dinosaur. It lived about 166 to 164 million years ago in the middle Jurassic Period. Its remains were found in Argentina. The animal was a fairly large, lightly built, bipedal, land-based carnivore. It grew up to 6.6 m (21.7 ft) long.