A stoat, ferret, mink, otter, fisher, pine marten etc… Why are there so many different names for a weasel? That’s because many of them are actually different species; some of which aren’t really weasels at all!
Mustelidae (from Latin mustela, weasel) are a family of carnivorous mammals.
The Mustelidae in general are phylogenetically relatively primitive and so were difficult to classify until genetic evidence started to become available. The increasing availability of such evidence may well result in some members of the family being moved to their own separate families, as has already happened with the skunks, previously considered to be members of the mustelid family.
Mustelids vary greatly in size and behavior. The least weasel is not much larger than a mouse. At the other end of the scale, giant otter can measure up to 2.4 metres (7.9 ft) in total length, while sea otters can exceed 45 kilograms (99 lb). Some mustelids like the ferret and tayra have been domesticated. Others are used for hunting, pest control or fur trade.
As well as the most species-rich family in the order Carnivora, the family Mustelidae is one of the oldest. Mustelid-like forms first appeared about 40 million years ago in the Oligocene epoch, roughly coinciding with the appearance of rodents. The direct ancestors of the modern mustelids first appeared about 15 million years ago.
– Source from Wikipedia. The information above needs to be edited with our own words.