Piatnitzkysaurus

*Piatnitzkysaurus floresi*

***Piatnitzkysaurus*** (/ˌpiːətnɪtskiːˈsɔːrəs/ pee-ət-NYITS-kee-SOR-əs meaning "Piatnitzky's lizard") 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 6.6 m (21.7 ft) long.

## Discovery and naming

The holotype specimen of *Piatnitzkysaurus*, PVL 4073, was collected during expeditions in 1977, 1982, 1983 at the Canadon Asfalto Formation in sediments that were deposited during the Callovian stages of the Jurassic period, approximately 164 to 161 million years ago. Once thought to be a basal carnosaur, it may instead be a megalosauroid. In total two partial skeletons are known (a fractured skull and parts of two postcranial skeletons, among which paratype MACN CH 895) and show that *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. It had robust arms and powerful hind legs with four toes on each foot. Its ischium is 423 millimetres (16.7 in) long. Its braincase resembles that of another megalosauroid, the megalosaurid *Piveteausaurus* from France. A general resemblance to the theropod *Allosaurus* was also noted by Benton (1992).

The type species, *Piatnitzkysaurus floresi*, was described by Jose Bonaparte in 1979. It was named to honor Alejandro Matveievich Piatnitzky (1879–1959), a Russian-born Argentine geologist.

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. Once thought to be a basal carnosaur, it was later classified as a megalosauroid.

## Description

In total, two partial skeletons are known (a fractured skull and parts of two postcranial skeletons, among which paratype MACN CH 895) and is the most completely known theropod from the Middle-Late Jurassic Period of the Southern Hemisphere. *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. It had robust arms and powerful hind legs with four toes on each foot. Its ischium is 423 millimetres (16.7 in) long. Its braincase resembles that of another megalosauroid, the megalosaurid *Piveteausaurus* from France.

A general resemblance to the theropod *Allosaurus* was noted by Benton (1992); however there are key differences between the two. The scapular blade of *Piatnitzkysaurus* is shorter and wider than more derived tenaurans. The humerus represents 50 percent of the length of the femur, which is also a primitive condition present among basal theropods. 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*. Also primitive is the wide contact between the pubis and ischium, a condition that is much different than that of *Allosaurus* and more derived tetanurans, in which contact is reduced. The pubis of *Piatnitzkysaurus* also has a distal foot that is more modestly developed than in *Allosaurus*.

Due to the strong resemblance to *Piatnitzkysaurus*, it has been suggested that the sister taxa *Condorraptor* could be better interpreted as the result of individual variation within the species, and not as separate taxa. 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*.

### Braincase

The braincase of *Piatnitzkysaurus* has been reviewed in detail by Oliver Rauhut; the review constitutes one of the few detailed accounts of braincase morphology in basal theropods. *Piatnitzkysaurusis* the only member of Piatnitzkysauridae with cranial material preserved, for which two maxillae, a frontal, a braincase, and a partial dentary are known. *Piatnitzkysaurus* is among the most basal members of the tetanurans and is important for understanding not only Middle Jurassic theropod evolution in the Southern Hemisphere, but also for knowledge of character evolution at the base of tetanurae.

The braincase of the holotype of *Piatnitzkysaurus floresi* (PVL 4073) is rather well preserved and shows no signs of deformation. The sutures between the individual bones of the skull are only partially visible, which indicates that the holotype represents a subadult individual. This is also consistent with the state of ossification in the post-cranial skeleton. An unusual feature of the braincase is the parasphenoid recess, which has only been described in two other non-avian theropods, *Sinovenator* and *Sinornithosaurus*. Given the distant phylogenetic position of the basal tetanuran *Piatnitzkysaurus* and the advanced maniraptoran and deinonychosaurian taxa *Sinovenator* and *Sinorntihosaurus*, the presence of this recess represents a convergence and can be considered an autapomorphy of the former genus. Another noteworthy aspect of the braincase is the prominent hook-like basisphenoidal wing, a feature that is also found in other theropods such as *Ceratosaurus*, *Allosaurus*, and *Tyrannosaurus*.

## Classification

The most basal clade within Megalosauroidea contains *Condorraptor*, *Marshosaurus*, *Piatnitzkysaurus* and *Xuanhanosaurus*. The next most basal clade comprises *Chuandongocoelurus* and *Monolophosaurus*. However, the affiliation of these clades with Megalosauroidea is poorly supported by tree support metrics, and it is possible that they will be classified outside of Megalosauroidea by future analyses.

## JPInstitute.com Description

This medium-sized meat-eater was a South American cousin of Allosaurus. It was found in the same area as Patagosaurus and probably fed upon those large plant-eaters when they were still young (and small).

Piatnitzkysaurus seems to have been a more primitive allosaurid in a number of its features. It is considered by some to be a "root" dinosaur at the base of the carnosaur family tree. This family tree, however, is not yet universally accepted.

## Appearance in other media

### *Jurassic Park*

* Piatnitzkysaurus appeared in the Jurassic World toys.

## Links

https://web.archive.org/web/20030405120404/http://www.jpinstitute.com/dinopedia/dinocards/dc\_piatn.html

## References

1. ↑ Bonaparte, 1979. Dinosaurs: A Jurassic assemblage from Patagonia. Science. 205, 1377–1379.
2. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `benson2010`
3. ↑ Mazzetta, G. V., Fariiia, R. A., & Vizcaino, S. F. 2000. On the palaeobiology of the South American homed theropod Carnotaurus sastrei Bonaparte. In: B. Perez-Moreno, T.R. Holtz Jr., J.L. Sanz, & J.J. Moratalla (eds.), Aspects of Theropod Paleobiology, Special Volume - Gaia 15, 185-192. Lisbon.
4. ↑ Brusatte, S. L., Benson, R. B. J., and Xu, X. 2010. The evolution of large-bodied theropod dinosaurs during the Mesozoic in Asia. Journal of Iberian Geology, 36, 275-296
5. ↑ Rauhut, 2004. Braincase structure of the Middle Jurassic theropod dinosaur *Piatnitzkysaurus*. Canadian Journal of Earth Science. 41, 1109–1122.
6. ↑ Benton, M. (1992). Dinosaur and other prehistoric animal factfinder. 1st American ed. New York: Kingfisher Books. Chicago / Turabian - Author Date Citation