Mustelidae

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

Several mustelids, including the mink, the sable (a type of marten), and the stoat (ermine), possess furs that are considered beautiful and valuable, so have been 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 (Neogale macrodon) 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.

The ferret, a domesticated form of the European polecat, is a fairly common pet.

Evolution and systematics

Mustelidae is a subfamily in Musteloidea, a superfamily of mammals that is united by shared skull and teeth characteristics. Mustelids are believed to have separated from their next closest related family, Procyonidae, around 29 million years ago.

The oldest known mustelid from North America is Corumictis wolsani from the early and late Oligocene (early and late Arikareean, Ar1–Ar3) of Oregon. Middle Oligocene Mustelictis from Europe might also be a mustelid.

Other early fossils of the mustelids were dated at the end of the Oligocene to the beginning of the Miocene. Which of these forms are Mustelidae ancestors and which should be considered the first mustelids is unclear.

The fossil record indicates that mustelids appeared in the late Oligocene period (33 Mya) in Eurasia and migrated to every continent except Antarctica and Australia (all the continents that were connected during or since the early Miocene). They reached the Americas via the Bering land bridge.

Classification

The 69 recent mustelids (67 extant species) are classified into eight subfamilies in 22 genera:

Fossil mustelids Extinct genera of the family Mustelidae include:

• Brachypsalis
• Chamitataxus
• Corumictis
• Cyrnaonyx
• Ekorus
• Enhydriodon
• Eomellivora
• Hoplictis
• Megalictis
• Oligobunis
• Oaxacagale
• Plesictis
• Sthenictis
• Sonitictis
• Teruelictis
• Trochictis