Mustelidae


The Mustelidae are a family of carnivorous mammals, including weasels, badgers, otters, ferrets, martens, minks, and wolverines, among others. Mustelids are a diverse group and form the largest family in the order Carnivora, suborder Caniformia. Mustelidae comprises about 56–60 species across eight subfamilies.

Variety

Mustelids vary greatly in size and behaviour. The least weasel can be under a foot in length, while the giant otter of Amazonian South America can measure up to and sea otters can exceed in weight. The wolverine can crush bones as thick as the femur of a moose to get at the marrow, and has been seen attempting to drive bears away from their kills. The sea otter uses rocks to break open shellfish to eat. The marten is largely arboreal, while the European badger digs extensive networks of tunnels, called setts. Some mustelids have been domesticated: the ferret and the tayra are kept as pets, 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.
As well as being one of the most species-rich families in the order Carnivora, the family Mustelidae is one of the oldest. Mustelid-like forms first appeared about 40 million years ago, roughly coinciding with the appearance of rodents. The direct ancestors of the modern mustelids first appeared about 15 million years ago.

Characteristics

Within a large range of variation, the mustelids exhibit some common characteristics. They are typically small animals with elongated bodies, short legs, short, round ears, and thick fur. Most mustelids are solitary, nocturnal animals, and are active year-round.
With the exception of the sea otter, they have anal scent glands that produce a strong-smelling secretion the animals use for sexual signaling and for marking territory.
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 more favorable environmental conditions. Reproduction has a large energy cost and 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.
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. With variation between species, the most common dental formula is.

Ecology

The martens, fisher and tayra are partially arboreal, while badgers are fossorial. A number of mustelids have aquatic lifestyles, ranging from semiaquatic minks and the several species of river otters to the fully aquatic sea otter. The sea otter is one of the few non-primate mammals known to use a tool 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.
The skunks were formerly included as a subfamily of the mustelids, but are now regarded as a separate family. The mongoose and the meerkat bear a striking resemblance to many mustelids, but belong to a distinctly different suborder—the Feliformia and not the Caniformia. Because the mongooses and the mustelids occupy similar ecological niches, convergent evolution has led to similarity in form and behavior.

Diversity

The oldest known mustelid from North America is Corumictis wolsani from the early and late Oligocene of Oregon. Middle Oligocene Mustelictis from Europe might be a mustelid as well. Other early fossils of the mustelids were dated at the end of the Oligocene to the beginning of the Miocene. “There is debate regarding which fossils from these epochs represent possible ancestral forms that led to Mustelidae and which fossils represent the first modern mustelids.” From the fossil record we can see that Mustelids appeared in the late Oligocene period in Eurasia and migrated throughout the continents. They inhabit every continent except Antarctica and Australia. They migrated all throughout the continents that were connected during the early Miocene. They made their way to North and South America via the Bering land bridge.

Human uses

Several mustelids, including the mink, the sable and the stoat, boast exquisite and valuable furs, and have been accordingly hunted since prehistoric times. From the early Middle Ages, the trade in furs was of great economic importance for northern and eastern European nations with large native populations of fur-bearing mustelids, and was a major economic impetus behind Russian expansion into Siberia and French and English expansion in North America. In recent centuries, fur farming, notably of mink, has also become widespread and provides the majority of the fur brought to market.
One species, the sea mink of New England and Canada, was driven to extinction by fur trappers. Its appearance and habits are almost unknown today because no complete specimens can be found and no systematic contemporary studies were conducted.
The sea otter, which has the densest fur of any animal, narrowly escaped the fate of the sea mink. The discovery of large populations in the North Pacific was the major economic driving force behind Russian expansion into Kamchatka, the Aleutian Islands, and Alaska, as well as a cause for conflict with Japan and foreign hunters in the Kuril Islands. Together with widespread hunting in California and British Columbia, the species was brought to the brink of extinction until an international moratorium came into effect in 1911.
Today, some mustelids are threatened for other reasons. Sea otters are vulnerable to oil spills and the indirect effects of overfishing; the black-footed ferret, a relative of the European polecat, suffers from the loss of American prairie; and wolverine populations are slowly declining because of habitat destruction and persecution. The rare European mink Mustela lutreola is one of the most endangered mustelid species.
One mustelid, the ferret, has been domesticated and is a fairly common pet.

Systematics

The 56 living mustelids are classified into eight subfamilies in 22 genera.
Subfamily Taxidiinae
Subfamily Mellivorinae
Subfamily Melinae
Subfamily Helictidinae
Subfamily Guloninae
Subfamily Ictonychinae
Subfamily Lutrinae
Subfamily Mustelinae
Fossil mustelids
Extinct genera of the family Mustelidae include:
Multigene phylogenies constructed by Koepfli et al. and Law et al. found that Mustelidae comprises eight subfamilies. The early mustelids appear to have undergone two rapid bursts of diversification in Eurasia, with the resulting species only spreading to other continents later.
Mustelid species diversity is often attributed to an adaptive radiation coinciding with the Mid-Miocene Climate Transition. Contrary to expectations, Law et al. found no evidence for rapid bursts of lineage diversification at the origin of Mustelidae, and further analyses of lineage diversification rates using molecular and fossil-based methods did not find associations between rates of lineage diversification and Mid-Miocene Climate Transition as previously hypothesized.