Piatnitzkysaurus is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of theropod dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

. It is known from the Canadon Asfalto Formation

Cañadon Asfalto Formation

-Paleofauna:-References:* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka : The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2....

, Middle Jurassic

Middle Jurassic

The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....

 (Callovian

Callovian

In the geologic timescale, the Callovian is an age or stage in the Middle Jurassic, lasting between 164.7 ± 4.0 Ma and 161.2 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian....

 stage) of what is now Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

. Once thought to be a basal

Basal (phylogenetics)

In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...

 carnosaur, it may instead be a megalosauroid

Megalosauroidea

Megalosauroidea is a group of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period.-Classification:...

. Partial skeletons are known (two fractured skulls and parts of the postcrania

Postcrania

Postcrania[p] in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g...

l skeleton) and show Piatnitzkysaurus was a lightly built medium-sized bipedal carnivore with robust arms around 4.3 metres (14.1 ft) long and around 450 kilograms (992.1 lb) in mass, though such estimates apply to the holotype

Holotype

A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

, which is a subadult. Its ischium is 423 millimetres (16.7 in) long. Its braincase resembles that of another megalosauroid, the megalosaurid Piveteausaurus

Piveteausaurus

Piveteausaurus is a genus of theropod dinosaur known from a partial skull discovered in the Middle Jurassic Marnes de Dives formation of Calvados, in northern France.-History and description:...

from France.
The type species, Piatnitzkysaurus floresi, was described by Jose Bonaparte

José Bonaparte

José Fernando Bonaparte, Ph.D. , is an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists like Rodolfo Coria...

in 1979.