Piatnitzkysaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Piatnitzkysauridae

Genus:Piatnitzkysaurus

Species:Piatnitzkysaurus floresi

Introduction

Piatnitzkysaurus was a medium-sized predatory dinosaur that lived in Middle Jurassic South America. This species is one of a diverse branch of predators that thrived in the Southern Hemisphere in the Jurassic and Cretaceous periods.

In the Triassic period, the continents of the world were united in a single supercontinent known as Pangaea. In the Jurassic and Cretaceous, tectonic movement caused Pangaea to split apart, giving rise to two supercontinents, Laurasia in the north and Gondwana in the south. After the breakup of Pangaea, isolated dinosaur populations evolved into unique southern and northern assemblages of species.

Piatnitzkysaurus was a member of a group of predatory dinosaurs that evolved before the breakup of Pangaea but expanded in Gondwana, while closely related branches of the same lineage dominated in Laurasia. Piatnitzkysaurus was a relatively rare species that lived in the woodlands and forests of what is now Argentina.

Classification

Paleontologists utilize two methods to organize animals into different groups. Linnaean taxonomy, or “systematics,” groups animals according to overall physical similarity, while an alternative method, “cladistics,” uses groups called “clades” in an effort to represent the evolutionary relationships between species.

According to the Linnaean system, Piatnitzkysaurus belongs to the order Saurischia, because of the “lizard-like” orientation of the animal's hips (a longstanding distinction in dinosaur classification that has been challenged by some scientists). From there, the species is placed in the suborder Theropoda, which were primarily bipedal carnivores. Most paleontologists further place the species in the superfamily Megalosauridae, which were large-skulled theropods generally found in the Early and Middle Jurassic, and the family Piatnitzkysauridae. Piatnitzkysaurus floresi is the type species within the genus.

Cladistic analysis also uses the clade Theropoda, defined by the presence of a forked bone called a furcula, or “wishbone,” as well as characteristic features of the skull and legs. The dinosaur also falls under the clade Tentanurae, which contains theropods with teeth only in the front of their jaws, characteristic joints in the jaws, and a similar skull design. Further classification of Piatnitzkysaurus and similar species varies, with some disagreement on the arrangement of clades such as Megalosauroidea, Megalosauridae, and Spinosauroidea.

Anatomy

Piatnitzkysaurus was a medium-sized predator, reaching an estimated length of between 4 and 4.5 meters (13.1–14.7 ft) and weighing between 250 and 300 kilograms (551–661 lbs). Like all theropods, the species was bipedal, with longer rear legs terminating in three-toed, clawed feet. Unlike some later theropods in North America, Piatnitzkysaurus had relatively strong and well-developed arms, which may have helped to grasp prey.

The species had a long, thick skull with sharp, curved teeth in the front of the jaws. The eyes were large and set in front of the skull. Piatnitzkysaurus was relatively lightly built and may have been able to run at significant speeds. Its tail was thick and stiff, likely serving as a counterbalance.

Like many dinosaurs, Piatnitzkysaurus was probably covered in mosaic scales and may have been cryptically colored to aid in predation. Compared to later theropods, the anatomy of Piatnitzkysaurus indicates that the species was relatively primitive.

Intelligence

Piatnitzkysaurus was probably similar in intelligence to a small bird or large reptile, which may have made it more intelligent than many of the herbivorous dinosaurs living in its environment.

Reproduction and Population

Paleontologists believe that most dinosaurs were oviparous, rather than viviparous, and eggs have been found for many dinosaur species. Paleontologists have not found eggs or juvenile specimens of Piatnitzkysaurus and are therefore uncertain about the animal's reproductive behavior. Eggs have been found for other theropod species, indicating that at least some species laid eggs on the ground in shallow nests excavated from the soil. Some smaller dinosaur species may have brooded their eggs like modern birds, using body heat to incubate their young. Paleontologists believe that larger dinosaurs were unable to sit on their eggs and instead covered their nests in shallow vegetation, which insulated the eggs and provided protection from scavengers.

Diet

The teeth of Piatnitzkysaurus indicate that the species was predatory, probably feeding on small reptiles, amphibians, and dinosaurs in its environment. In addition to a variety of smaller animals, Piatnitzkysaurus may have preyed on the Argentinean sauropods, large herbivores characterized by their small heads and long necks. Several species of sauropods were present in Argentina, including the large Patagosaurus.

Although paleontologists believe that some theropods hunted in packs, evidence for social hunting has not been found for Piatnitzkysaurus. The species was likely an opportunistic hunter, taking a variety of large prey and perhaps feeding on carrion when available.

Behavior

Piatnitzkysaurus has been compared to its North American cousin Allosaurus, which some paleontologists believe hunted and perhaps traveled in family groups. By contrast, Piatnitzkysaurus may have been a solitary predator, stalking the woodlands and open scrub of Argentina and preying on a variety of animals.

The sauropod herbivores, which appear to have been common in mid-Jurassic Argentina, are believed to have been among the least intelligent dinosaurs. Predators like Piatnitzkysaurus may have relied upon superior intelligence to aid in overcoming the superior size of the large herbivores in its environment.

Habitat and Other Life Forms

Middle Jurassic Argentina was a patchwork of habitats ranging from dry scrub to lush forests. The cycads, a group of plants that dominated during the Jurassic, formed large forests and evolved into a variety of species from tall, palm-like trees to small ground vegetation. The skies were dominated by pterosaurs, flying reptiles that evolved alongside the dinosaurs and were the dominant flying vertebrates in the Mesozoic.

Few dinosaur species have been uncovered from Middle Jurassic sediments in Argentina. The sauropod species found here are thought to be direct ancestors of many of the large species that dominated the terrestrial environment in the Late Jurassic and produced some of the largest terrestrial animals in the history of the planet. In the Middle Jurassic, Argentina was home to a number of early sauropod species, including Patagosaurus and Volkheimeria.

In addition to dinosaurs, Piatnitzkysaurus's environment included a large number of terrestrial reptiles, including the sphenodonts, a group of extinct reptiles that filled a similar niche to modern lizards. The Middle Jurassic also saw an expansion and radiation of the crocodyliforms, ancestors of modern crocodiles that evolved into a variety of species, including aquatic species, marine species, and terrestrial predators.

Research

Piatnitzkysaurus was described by Argentine paleontologist José Bonaparte in the 1979. Fragmentary remains of other specimens have been found since the species was first discovered. Much research has focused on classification, with considerable debate surrounding theropods in general. For a time many paleontologists believed that Piatnitzkysaurus and related species may have represented an evolutionary lineage that also included the spinosaurs, which were semi-aquatic dinosaur predators that were very successful in the southern hemisphere. However, later analysis generally supported the idea that the Piatnitzkysauridae branched off earlier than the Spinosauridae and the Megalosauridae (both considered by some as Megalosauria). Theropod taxonomy remains unstable overall.

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