Piatnitzkysaurus (pron.:"PEA-at-NITS-key-SORE-us") is an extinct genus of megalosaurid theropod dinosaur that lived approximately 164 to 161 million years ago during the middle part of the Jurassic Period in what is now Argentina. It was named to honor Alejandro Mateievich Piatnitzky (1879–1959), a Russian-born Argentine geologist. Piatnitzkysaurus was a moderately large, lightly built, bipedal, ground-dwelling carnivore, that could grow up to 4.3 m (14.1 ft) long.