Purussaurus

Purussaurus is an extinct genus of giant caiman that lived in South America during the Miocene epoch, from the Colhuehuapian to the Montehermosan in the SALMA classification. It is known from skull material found in the Brazilian and Peruvian Amazon, Colombian Villavieja Formation, Panamanian Culebra Formation and the Urumaco and Socorro Formations of northern Venezuela.
Description.
The skull length of the largest known individual of the type species, "P. brasiliensis" is .
It has been estimated that "P. brasiliensis" reached about in length, weighing about . Another estimate gave a larger size of in length and in weight, with a mean daily food intake of . However, these proportions have been met with a lot of scrutiny, and it is more likely that "Purussaurus" reached only long and . As only skulls have been found, the actual length is not certain. Bite force has been estimated to be around 52,500 N (around 5.3 metric tons-force). The large size and estimated strength of this animal appears to have allowed it to include a wide range of prey in its diet, making it an apex predator in its ecosystem. As an adult, it would have preyed upon large to very large vertebrates such as the xenarthrans and notoungulates present, with no real competition from sympatric, smaller, carnivores. Researchers have proposed that the large size of "Purussaurus", though offering many advantages, may also have led to its vulnerability. The constantly changing environment on a large geological scale may have reduced its long-term survival, favoring smaller species more resilient to ecological shifts. In other words, it was over-specialised and couldn't survive when its habitat changed, unlike smaller related species of caiman.
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.
Upper estimates indicate that Purussaurus was capable of generating 69,000 N (around 7 metric tons) of pressure with its jaws.
Paleoecology.
"Stupendemys", crocodilians including "Charactosuchus", "Gryposuchus", and "Mourasuchus", "Anhinga" birds, and mammals including sloths, bats, rodents such as relatives of the modern capybara weighing up to 700 kilograms (1540 lb), the primate "Stirtonia", and river dolphins were all present, and would probably all have been eaten by "Purussaurus". River, floodplain, 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". This fauna dates from 13 million years ago, in the Laventan stage of the Late Miocene.
Distribution.
Fossils of "Purussaurus" have been found in: