The Giant Otter (Pteronura brasiliensis) is an amphibious, mammalian carnivore native to South America. About the length of an ault human being, it is the longest member of the mustelidae, or weasel family, a globally successful group of predators. Unusually for a mustelid, the Giant Otter is a social species, with family groups typically supporting three to eight members. The groups are centred around a dominant breeding pair and are extremely cohesive and cooperative. Although generally peaceful, the species is territorial and aggression has been observed between groups. The Giant Otter is exclusively active during daylight hours. It is the noisiest otter species and distinct vocalizations have been documented that indicate alarm, aggressiveness, and reassurance.