The Mustelidae (; from Latin mustela, weasel) are a diverse family of carnivoran mammals, including weasels, badgers, otters, sea otters, polecats, martens, grisons and wolverines. Otherwise known as mustelids (), they form the largest family in the suborder Caniformia of the order Carnivora with between 66 to 70 species in nine subfamilies.
Variety Mustelids vary greatly in size and behaviour. The smaller variants of the least weasel can be under 20 cm (8 in) in length, while the giant otter of Amazonian South America can measure up to 1.7 m (5 ft 7 in) and sea otters can exceed 45 kg (99 lb) in weight. Wolverines can crush bones as thick as the femur of a moose to get at the marrow, and have been seen attempting to drive bears away from their kills. The sea otter uses rocks to break open shellfish to eat. Martens are largely arboreal, while European badgers dig extensive tunnel networks, called setts. Only one mustelid has been domesticated: the ferret. Tayra are also kept as pets (although they require a Dangerous Wild Animals licence in the UK), or as working animals for hunting or vermin control. Others have been important in the fur trade—the mink is often raised for its fur. Mustelidae is one of the oldest and most species-rich families in the order Carnivora. Mustelid-like forms appeared about 40 million years ago (Mya), roughly coinciding with the appearance of rodents. The common ancestor of modern mustelids appeared about 18 Mya.
Characteristics
Within a large range of variation, the mustelids exhibit some common characteristics. They are typically small animals with elongated bodies, short legs, short skulls, short, round ears, and thick fur. Mustelids' long, slender body structure is adapted to three main lifestyles: terrestrial; arboreal; and aquatic/semi-aquatic. They exhibit digitigrade or plantigrade locomotion, with five toes on each foot, enabling them to move in different ways (i.e., digging, climbing, swimming). Most mustelids are solitary, nocturnal animals, and are active year-round. Their dense fur, often serving as natural camouflage, undergoes seasonal changes to help them adjust to varying environmental conditions. With the exception of the sea otter they have anal scent glands that produce a strong-smelling secretion the animals use for sexual signalling and marking territory.
Reproduction Mustelids exhibit sexual dimorphism, with males being larger than females, but degree varies between species as well as geographically within species. Male mustelids have a bifurcated penis and baculum. Most mustelid reproduction involves embryonic diapause. The embryo does not immediately implant in the uterus, but remains dormant for some time. No development takes place as long as the embryo remains unattached to the uterine lining. As a result, the normal gestation period is extended, sometimes up to a year. This allows the young to be born under favourable environmental conditions. Reproduction has a large energy cost, so it is to a female's benefit to have available food and mild weather. The young are more likely to survive if birth occurs after previous offspring have been weaned.
Diet Mustelids are predominantly carnivorous, although some eat vegetable matter at times. While not all mustelids share an identical dentition, they all possess teeth adapted for eating flesh, including the presence of shearing carnassials. One characteristic trait is a meat-shearing upper-back molar that is rotated 90°, towards the inside of the mouth. With variation between species, the most common dental formula is 3.1.3.13.1.3.2, for a total of 34 teeth.
Ecology
The fisher, tayra, and martens are partially arboreal, while badgers are fossorial. A number of mustelids have aquatic lifestyles, ranging from semiaquatic minks and river otters to the fully aquatic sea otter, which is one of the few nonprimate mammals known to use tools while foraging. It uses "anvil" stones to crack open the shellfish that form a significant part of its diet. It is a "keystone species", keeping its prey populations in balance so some do not outcompete the others and destroy the kelp in which they live. The black-footed ferret is entirely dependent on another keystone species, the prairie dog. A family of four ferrets eats 250 prairie dogs in a year; this requires a stable population of prairie dogs from an area of some 500 acres (200 ha).
Animals of similar appearance Skunks were previously included as a subfamily of the mustelids, but DNA research placed them in their own separate family (Mephitidae). Mongooses bear a striking resemblance to many mustelids, but belong to a distinctly different suborder—the Feliformia (all those carnivores sharing more recent origins with the cats) and not the Caniformia (those sharing more recent origins with the dogs). Because mongooses and mustelids occupy similar ecological niches, convergent evolution has led to similarity in form and behaviour.
Human uses
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