Purussaurus

Purussaurus is an extinct genus of giant caiman that lived in South America during the Miocene epoch, from the Friasian to the Huayquerian in the SALMA classification. It is known from skull material found in the Brazilian and Peruvian Amazon, Argentina, Colombian Villavieja Formation, Panamanian Culebra Formation, Urumaco and Socorro Formations of northern Venezuela.

Description

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The skeletal anatomy of P. mirandai shows some adaptations for more upright limb orientation or weight support. Unlike all other members of the crown Crocodylia, which have two sacrals, P. mirandai have three.

The teeth vary between the three species of Purussaurus, but are always around 50 mm (2 in) long and curve slightly backwards. They have small ridges along two of the edges which resemble those in ziphodonts. This indicates that Purussaurus hunted large vertebrates, as these ridges are used for puncturing and holding on to flesh. The teeth are slightly flattened at the top and are roughly conical, which means that they would have been unlikely to break on impact with a thick bone. Teeth at the anterior are taller and more pointed, whereas those at the posterior are lower and more rounded.

Purussaurus is one of the largest known crocodyliformes ever to have existed. Three other extinct crocodyliformes, Sarcosuchus, Deinosuchus, and Rhamphosuchus had similar body sizes. Sarcosuchus and Deinosuchus had similar proportions, but both were geologically much older, dating from the Early and Late Cretaceous, respectively. One study also indicates that Purussaurus may have been heavier than either Sarcosuchus or Deinosuchus, as it had a much broader, shorter snout and this would require a thicker, stronger neck to support the larger head. Rhamphosuchus lived around the same time as Purussaurus, but was slightly smaller, had a more gharial-like snout and lived in India. During the summer of 2005, a Franco-Peruvian expedition (the Fitzcarrald expedition) found new fossils of Purussaurus in the Peruvian Amazon (600 km from Lima). Analysis of a biomechanical model of the skull of Purussaurus indicated that it was capable of performing the "death roll" maneuver used by extant crocodilians to subdue and dismember their prey.

All sense organs (eyes, ears, nostrils) were at the very top of the head, indicating that Purussaurus was an ambush predator like many modern caimans.

Paleoecology

File:Purussaurus life reconstruction.png

Life reconstruction

The probable diet of Purussaurus likely included the extinct turtle Stupendemys, crocodilians including Charactosuchus, Gryposuchus, and Mourasuchus, Anhinga birds, and mammals including: sloths, bats, rodents related to the modern capybara (Josephoartigasia) weighing up to 700 kilograms (1540 lb), the primate Stirtonia, and river dolphins. Rivers, floodplains, and lake environments were present. Marine and freshwater fish, turtles, crocodilians, and terrestrial and aquatic mammals are associated with Venezuelan P. mirandai. Its environment is described as tropical and coastal. The earlier Colombian P. neivensis lived alongside a massive variety of fauna, including astrapotheres like Granastrapotherium and Xenastrapotherium, the early species of Mourasuchus and Gryposuchus, and the terrestrial crocodyliform Langstonia. Bite marks on the tibia of a phorusrhacid from this locality are consistent with a caimanine, possibly a young individual of Purussaurus. This fauna dates from 13 million years ago, in the Laventan stage of the Late Miocene.

Etymology

The genus was named for the Purus River where its fossils were first found.

Distribution

Fossils of Purussaurus have been found in:

Miocene

• Solimões Formation, Brazil
• Honda Group and Castilletes Formation, Colombia
• Culebra Formation, Panama
• Fitzcarrald Arch and Pebas Formation, Peru
• Urumaco Formation, Urumaco and Socorro Formation, Venezuela
• Ituzaingó Formation, Argentina

See also

• Mourasuchus

External links

• Tetrapod Zoology post on Purussaurus
• Template:In lang UFAC
• Template:In lang Article about Purussaurus on DinosaurusBlog