The giant otter (Pteronura brasiliensis) of South America is the longest otter, sometimes reaching over 5ft in body length alone. They're also one of the more social otter species, living in groups of anywhere from two to twenty members. Giant otters are currently listed as endangered by the IUCN. In the past they were extensively hunted for their pelts, and today habitat loss and degradation from human activity and climate change remains a continuous threat. [src: IUCN]