August 25 , 2016

by Vasika Udurawane

Purussaurus is one of the biggest, yet most poorly understood of all massive crocodilians. For a while not much was known about it besides its size and strength. Recently though, new scientific research is uncovering its most lethal secret: Its monstrous seven-ton bite.

The gigantic caiman Purussaurus is known mainly from impressive remains found in parts of Brazil, Colombia, Venezuela and the rest of the Amazon region. Discovered and named by Joao Barbosa Rodrigues, in 1892, the animal soon became known as one of the largest and most powerful freshwater predators ever.

Later, the huge blocky skulls of the beasts were uncovered. From these remains it was estimated that Purussaurus was among the largest crocodilians to have been found and one of the biggest reptiles to exist after the dinosaurs’ extinction. It was 12.5 meters long and weighed 8.4 tons, as long as a bus. But some finer details of the creature’s biology still remained a mystery. For example, it was not known exactly how Purussaurus killed its prey nor was its daily food intake known.

Recently, a team lead by Tito Aureliano of Rio de Janeiro's Federal University began to study the type and largest species in the genus, the colossal P. brasiliensis. The team published their discoveries in the scientific journal PLOS ONE. The giant caiman’s chunky head – the subject of Aureliano's research – was 1.5 meters in length, roughly as big as the entire body of some modern caiman species living today. For the study, the creature was compared with other crocodilian species like black caimans and both saltwater and Nile crocodiles. All of these animals have been measured previously for the strength of their bites and for their feeding behavior.

Aureliano and team revealed that the extinct Purussaurus needed roughly 40 kg (88 lb) of food daily. This is twenty times the requirement for the modern American alligator. It also had one of the strongest bites ever measured in any land carnivore. The team estimated that the creature could deliver a sustained pressure of 7 tons, far stronger even than Tyrannosaurus, the previous strongest biter on land. Team member Aline M. Ghilardi explains that like T. rex, Purussaurus was an unchallenged apex predator with no real competition from fellow carnivores. It was capable of taking on mammals weighing greater than a ton, and its skull was specially strengthened to withstand the pressures of such a force.

Most Purussaurus brasiliensis fossils are 8 million years old, dating back to the Late Miocene. These rocks revealed a massive system of lakes and wetlands known as the Pebas System, an area somewhat like an inland sea in the northern region of South America. It was very different from the Amazon of today, with the Andes still on the rise.

The fossil fauna of the varied Pebas environments included large aquatic birds. In the water were giant fish such as various huge catfish species still alive today. There were also several capybara-like rodents the size of water buffaloes, giant ground sloths and strange hoofed animals called notoungulates as big as a rhino. The Pebas was also dominated by several gigantic reptiles like the herbivorous turtle Stupendemys, as big as a car. Purussaurus also lived with several normal-sized caiman and gharial species and even some real leviathans nearly as big as itself.

But there was little competition among these creatures. Instead, there were varied environments in the extensive Pebas and a great deal of niche partitioning. While Purussaurus fed on nearly everything as an adult, its contemporaries ate fish or smaller prey. Aureliano and team had revealed a diverse wetland ecosystem dominated by carnivorous reptiles and very few mammalian predators. According to them, it was still a very fragile system and Purussaurus itself was among the most fragile components. Huge and powerful though it was, the creature was soon to be extinct in a few million years.

The Andes Mountains, now a dominant feature of South America, were still rising and this meant a shift in the drainage patterns in the Amazon region. According to Ghilardi, the change spelled disaster for the entire Pebas environment. During the Pliocene, the period succeeding the Miocene, the Pebas started draining out. It would soon become a system of rivers rather than a vast series of lakes and inland seas. Across the Amazon, smaller species were favored over larger ones. Many of the massive rodents and hoofed mammals would soon die or be replaced by newer species adapted to the new habitats.

The same went for the reptiles. There were three types of monster croc at the end of Miocene, with Purussaurus being one of them. Its huge size put a number of constraints on it. For one, it needed a great deal of food to fuel its bulk, and without its prey, the animal started to dwindle. In a rapidly changing world, the animal’s very size had become its handicap. The age of South America’s giant reptiles had ended for good and the terrifying likes of Purussaurus or its kin would never return.