Purussaurus

Purussaurus is an extinct genus of giant caiman that lived in South America during the Miocene epoch. This indicates how widespread the wetlands such a large caiman would require to survive were across South America in the Miocene.

The skull length of the largest known individual of the type species, P. brasiliensis is 1,453 millimetres. It has been estimated that P. brasiliensis reached about 10.3 metres in length, weighing about 5.16 metric tons. Another estimate gave a larger size of 12.5 metres in length and 8.4 metric tons in weight, with a mean daily food intake of 40.6 kilograms. However, these proportions have been met with a lot of scrutiny, and it is more likely that Purussaurus reached only 10.9 metres long and 5.6 metric tons.  As only skulls have been found, the actual length is not certain. Bite force has been estimated to be around 69,000 N (around 7 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.