The endangered South American mammal that is the longest member of the weasel family is the giant otter.
The giant otter, or giant river otter, is a mustelid found mainly in the Amazon Basin and Brazil’s Pantanal. It can reach about 1.8 metres in length, including its powerful tail, making it longer than other living members of the weasel family.
Unlike many mustelids, giant otters are highly social. Family groups usually contain three to eight animals centered on a breeding pair, and members cooperate in raising young and defending territories. They are active during the day and communicate with a wide range of vocalizations.
The sea otter is a tempting alternative, but it is not South American and belongs to a different ecological setting. Giant otters declined sharply after decades of hunting for their dense fur, especially during the 1950s and 1960s. Today, habitat degradation, pollution, and disturbance threaten their fragmented populations.