Biogeography of American Marten

Geography 316: Biogeography

In progress 12/11/2003

The Biogeography of the American Marten (Martes americana).

by Scott Sylva, student in Geography 316 Fall 2003

Thank you for visiting our site. This web page was written by a student in Geography 316: Biogeography and edited by the instructor, Barbara Holzman, PhD. All photos and maps are posted with specific copyright permission for the express use of education on these web pages. The students have tried to be as accurate as possible with the information provided and sources and references are cited at the end of each page.

Species Name: Martes americana

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Genus: Martes
Species: Martes americana
Common Names: American Marten, American Pine Marten, American Sable

Subspecies (not complete): M. a. americana M. a. caurina

M. a. brumlis M. a. humboldtensis (California)

M. a. oregenes M. a. sierrae (California)

(Chapman & Feldhamer, 1982)

Photo by Larry Colwell (2003)

Description of Species:

Martens are mink-like mammals in appearance and are slightly larger than a typical house cat in size (Chapman & Feldhamer, 1982). Male martens are larger than females, weighing about 1 ¼ - 2 ½ lbs and 14 ½ - 20 ½ inches in length. A female marten is 1 - 1 ½ lbs and 12 ½ - 17 inches long (Pickett 2003). Martens have a sharp pointed face, bushy tail, a thick coat of fur and five toes on each foot with toepads covered by fur most of the year (Chapman & Feldhamer, 1982). Claws on a marten are sharp, helping with mobility in climbing trees, and they have relatively large eyes and ears compared to their body (Parker, 1990; Nowak, 1991). In the summer, a marten’s coat is thinner than in winter and the overall color can vary from season to season or region to region. The coat is typically a golden brown color, but can range from dark brown to full yellow (Nowak, 1991). Generally, the fur on a marten’s face and head are lighter in color than the rest of the body and the coat darkens frequently to near black on its underbelly and feet (Chapman & Feldhamer, 1982).

According to Robert Pickett, a naturalist for the Potomac Appalachian Trail Club, martens are the most arboreal of all weasels and Parker (1990) says they use their long tails as rudders as they scurry across tree branches. Martens can be quite agile and fast, often jumping from tree to tree to pursue prey, and have been known to fall 60ft from trees and land with ease. Martens also use their claws to climb down trees, which they do head first like a squirrel (Parker, 1990). Martens have a highly developed sense of smell and have scent glands on their anus and abdomen, the latter of which is used to mark travel routes on trees. This helps to facilitate fast movement across branches in search of prey (Parker, 1990; Chapman & Feldhamer, 1982). A marten’s dentition and skull size are different from other similar species. Where a similar mink (Mustela vison) will have 3 molars, a marten will have 4. A marten also differs from similar-sized fishers by a smaller skull length (typically 80 to 90 mm). The dental formula of a marten is incisor 3/3, canine 1/1, premolar 4/4, and molar 1/2; a total of 38 teeth (Chapman & Feldhamer, 1982). Martes having four molars is one of the distinguishing features that separate them from their closest relative, the genus Mustela (weasels) (Powell, 1993).

Photo by John Marriot (2003) (http://www.wildernessprints.com).

Natural History:

Eating habits:
The marten has often been referred to as “opportunistic” when it comes to its food habits (Chapman & Feldhamer, 1982; Pickett). Small mammals, such as mice and voles, birds, insects, and fruit make up the main diet of a marten. Foods preferrences can be somewhat linked to seasons. In all seasons, but particularly the winter, martens prefer voles & mice (such as the red-backed vole (Clethrionomys gapperi)), but have also been known to search for ground squirrels, chipmunks and snowshoe hares. In early summer, they take advantage of small birds and their freshly laid eggs. Late summer brings an abundance of fruits and berries, of which blueberries are preferred, being the most easily accessible to the marten. Insects are also consumed throughout the year, but are in abundance in early fall (Chapman & Feldhamer, 1982). As up to 80% of a marten’s diet is animal prey, they spend much of their time foraging for food, both in trees and on the forest floor. In the winter, martens will tunnel under the snow, usually near felled logs, to track mice and voles, and have been known to cache food (Pickett 2003). Martens will travel great distances, even retracing their own tracks, looking in every crevice, log, stump, or tunnel for food (Snyder, 1991).

Mating, Reproduction & Birth:
Martens mate in the summer months, usually June to August (Nowak, 1991). Martens are polygamous and females will often mate with more than one male in a season. They also will mate several times during a given day (Chapman & Feldhamer, 1982). Females tend to become more aggressive during mating, as do males who often fight with other males to mate with a female (Chapman & Feldhamer, 1982). To attract a mate, females will urinate or use their abdominal scent glands to mark the ground. They will also become very vocal; grunting, screaming, or growling to attract a male. According to work gathered by Chapman & Feldhamer (1982, courtships can last as long as 15 days, during which much wrestling and playing occurs between potential mates. Once a mate is chosen, a male will grab the female’s skin from behind with its teeth and may hold on to or drag her around for up to 30 minutes before coitus begins. The act of mating itself can last for up to 90 minutes (Chapman & Feldhamer, 1982). After successful mating has occurred, the female becomes more aggressive towards the male and runs him off (Parker, 1990). Male martens do not participate any further than mating and have no role in child rearing (Chapman & Feldhamer, 1982).

A female marten’s pregnancy is an interesting process. Once an egg is fertilized, implantation is delayed and the egg remains as a blastocyst in the female’s uterus for 190-250 days (Chapman & Feldhamer, 1982). In February, the fertilized egg implants itself into the female marten’s uterus, and development takes about 28 days (Nowak, 1991). Infant martens are born live usually between March and April (Chapman & Feldhamer, 1982). On average, a marten will give birth to 2.6 babies, with a range of 1-5 (Nowak, 1991). The ratio of male to female births is 53:47; a pretty even distribution (Chapman & Feldhamer, 1982). At birth, a baby marten will be 3.6-4.8 inches long and weigh about one ounce. They are blind, deaf, and toothless, but already will have a thick coat of smooth fur. Mother martens look after their young for several months, not allowing them to leave the nest for at least two months, allowing the babies to suckle for nourishment (Parker, 1990). A marten baby will be weaned at six weeks of age (Pickett 2003) and, at 3.5 to 4 months old, a marten reaches its physical maturity and the mother will leave. A female marten will only have one litter per year (Buskirk & Zielinski, 1998). Despite being full size and mature at 4 months, a marten will not reach sexual maturity until 15-24 months of age. Martens can continue to be sexually reproductive up to 12 years in the wild (Nowak, 1991) or to at least 15 years of age if kept in captivity (Chapman & Feldhamer, 1982). In the wild, a marten’s life expectancy is in the range of 8-10 years, but can live as long as 15 to 17 years in captivity (Parker, 1990).

Home Range:
As mentioned earlier, martens are rather solitary creatures, except during mating season (Chapman & Feldhamer, 1982). The population distribution of a marten’s home range is about .5 to 1.7 martens per sq mile of good habitat (Nowak, 1991). Males are more exclusionary that females, they have wider territories (one male every 2-3 km) and will exclude most males. However, they are less likely to exclude other female martens (who range one every 1 km) and sightings in the wild have seen a male and a female traveling together (Chapman & Feldhamer, 1982). Male martens are most active in the dusk and evening. Females tend to be more active during the day and at dusk. Their activity is most dependent upon availability of food. Martens are very agile and energetic, often running up and down the forest floor, or through trees. They are also effective swimmers, being able to swim well underwater (Chapman & Feldhamer, 1982). As stated earlier, marten’s preferred resting and hunting areas are in felled and rotting logs, stumps and burrows. They do not like open fields as there is little protection provided from predators or adverse weather, but they will be seen perching on cut off tree tops in open spaces sunning themselves, or using the perch to get a good look around (Spencer, 1987). Martens are very curious creatures and it’s this trait that makes them easy to trap by hunters (Chapman & Feldhamer, 1982). A discussion of human impact on marten populations will be addressed later.

Predators:
According to Chapman & Feldhamer (1982), martens have few natural predators. It seems that the marten’s ability to quickly climb trees, out of the reach of most terrestrial predators, helps to mitigate their susceptibility to being killed. They do have natural predators and these include fishers, coyote, lynx, mountain lions, eagles and great horned owls. Martens are also subjected to inter- and intra-species competition, especially during late winter when food starts to become scarce. Competition from other species typically come from fishers, but also may come from other martens. Males are larger and hold more fat on their bodies than females, and so can fare better in the late months of winter. Because this size difference begins at birth, even female infants face stronger competition and are less suitable to compete for food with male litter mates. The biggest threat to martens are human activities, whether through trapping or by destruction of habitat (Chapman & Feldhamer, 1982). For more information about human impact on martens, see the interesting information section below.

Evolution:

American martens belong to the order Carnivora. Over 65 million years ago, carnivores roamed the earth as squirrel-sized creatures that fed mostly on insects (MacDonald 1992). These ancestral animals led to the Miacids, who were the first mammals to develop flesh-shearing teeth called carnassials, a distinguishing characteristic of most modern carnivores (MacDonald 1992, Powell 1993). Those scissor-like teeth were used to shear through flesh and gave the carnivores an advantage over other mammals and eventually allowed them to become the dominant predators in the Northern Hemisphere by 20-30 million years ago (MacDonald 1992). Carnivores also developed a set of teeth to the rear of the carnassial teeth that allowed them to take advantage of other foods such as fruits and vegetables. It was this ability to diversify their diets that allowed the carnivores to continue their success (MacDonald 1992).

Evolution of Order Carnivora, highlighting evolution of genus Martes (Powell, 1994).

In the late Eocene-early Miocene (34-40 mya), the Miacids evolved into two major groups, the Canoidea and Feloidea (Powell 1993). The latter branch diverged into the families Viverridea (civets), Felidae (cats), Hyaenidae (hyenas) and Herpestidae (mongooses) (MacDonald 1992). It is believed that the Mustelids (the weasel family, which includes martens) are descendents of the Canoidea family (Powell 1993). By the Miocene era, the four canoid families that are recognized today were distinguishable (Powell 1993): Canidae (dogs), Ursidae (bears), Procyonidae (raccoons) and Mustelidae (weasels) (MacDonald 1992). The fossil record is often difficult to discern regarding these early creatures, but it has been found that Mustelids diverged quickly from the remaining canoids, with the mustelids retaining the small, elongated bodies and the short, stocky legs with five toes that was a characteristic of the miacids (Powell 1993). Cooling of the world climate around 30 mya increased the world’s forests and allowed for the spread of Mustelids and other mammals. As this occurred, the Mustelids themselves began to diverge. Some Mustelids grew larger and evolved into modern day badgers and wolverines, while other groups retained a smaller and more tubular body in order to prey on burrowing animals (MacDonald 1992).
By the Pliocene (2-7 mya), martens were a distinct group within the weasel family (MacDonald 1984). The fossil record is not complete for the Martes genus, because of their small body size and boreal forest habitat (Powell 1993). However, fossil records of extinct fishers (M. paleosinensis and M. anderssoni) have been found in China (from 4.8 mya) and the earliest martens were found in lower Miocene beds in Germany (Anderson 1994). Still large gaps exist and the first Pine martens (M. martes) were found to be in Central and Western Europe around 100,000 ka and, between 65-122,000 ka, the American marten crossed Beringia into North America (Anderson 1994). The population in North America first spread throughout the boreal forests of all of North American, then became isolated in the eastern United States by the Laurentide Ice Sheet, then reinvaded Western Canada and Alaska upon its retreat (Anderson 1994). A later migration from Siberia also occurred, bringing marten (extinct M. nobilis) populations to the Sierras and Rockies (Anderson 1994). Some research has shown that M. nobilis may simply be a larger ancestor to the current “caurina” (M. americana caurina) subspecies (Anderson 1994).
As mentioned, the earliest martens appeared in Europe then spread quickly across temperate Asia and into North America. Today, there are three subgenera of marten, Pekania (fishers), Charronia (yellow-throated marten) and Martes (true martens) (Anderson 1994). The four boreal species of marten, M. martes, M. zebellina, M. melampus, and M. americana, replace each other geographically and have been referred to as a “superspecies” (Anderson 1994). However, because they all are similar in traits, behaviors, and habitat, some scientists feel that one day it may be discovered that these four species are shown to be one “circumboreal species” (Anderson 1994). The division of the American marten is under much debate. Some scientists argue as many as 14 different subspecies exist, while others feel many of those designations are merely arbitrary, and that there is more likely six different subspecies (Anderson 1994). The American marten has been distinguished into two subspecies groups, the “americana” and the “caurina”. These two groups are distinguished by several features including the shape of their skull, the auditory bullae, and the relative size of their upper molar (Anderson 1994). The “americana” group is typically associated with martens in Alaska, Canada, and the eastern United States. The “caurina” group, found in the western United States, such as the Sierras and Rockies, shows more similarities to the sable (M. zibellina) than to the “americana” group, and was the later migrant to North America (Anderson 1994). Research is also being done by some scientists who feel the American marten itself is not one, but two distinct species (M. americana and M. caurina) (Carr 2000). A distinction of two species, however, is still in debate.

Distribution:

Out of five species of true marten, the American marten is the only species found in North America (Chapman & Feldhamer, 1982). They are also one of only two in the genus Martes located in North America, the other being the large-bodied fisher (Martes pennanti) (Buskirk & Zielinski, 1998). They are most predominately located in boreal forests stretching from Alaska to the coast of Newfoundland. Their northern boundary is the boreal tree line in Alaska and Canada and the southern corresponding approximately to the 50ºF July isotherm (Chapman & Feldhamer, 1982; Buskirk & Zielinski, 1998). Martens can also be found in mountainous regions of California, the Rockies, New Mexico, New England and the Great Lakes (Nowak, 1991). Despite the virtually contiguous distribution across Canada and Alaska, in the western states the populations are rather fragmented. This is due in large part to the discontinuous forest coverage in the western states as well as human encroachment on their habitat (Gibilisco 1994).

Worldwide distribution of subgenus Martes (except stone marten). Green shows North American distribution of Martes americana
(Powell, 1994).

Distribution of M. americana in California, studied by Kucera et. all (1995). Red color shows distribution of subspecies M. a. sierrae, blue color shows subspecies M. a. humboldtensis.

In California, the two subspecies M. americana. sierrae and M. a. humboldtensis are distributed throughout the Sierra Nevada, the Coast Ranges and the California Cascades (Buskirk & Zielinski, 1998). In a survey completed by the US Forest Service, few traces of the M. a. humboldtensis were found along the coast of California; its historical habitat (Snyder, 1991). It was proposed that the subspecies has gone extinct, but it was noted that further study is needed (Snyder, 1991). Distributions in the Great Lakes regions have historically been diminished due to heavy trapping. But for various reasons, including reintroduction and trapping restrictions, populations have rebounded somewhat (Kucera et al., 1995). The location of the American marten in North America is thought to be one of a continuous global distribution of marten species across the world. The stone and beech marten (Martes foina) are found in deciduous and coniferous forest in Europe and Central Asia (MacDonald 1984). The sable (M. zibellina), European pine marten (M. martes), Japanese marten (M. melampus), and American marten stretch from the northern boreal forests of Europe, across Asia, to North America, almost in a continuous line (MacDonald 1984, Parker 1990). It has been theorized that while the stone marten developed as a sympatric species with the European marten, the sable, European, Japanese, and American martens are all a continuous, allopatric developed “superspecies”. They are all different enough in morphology to be considered separate species, but all come from a very similar ancestor (Powell, 1993). This may explain the marten’s almost continuous distribution across the boreal forests of the Northern Hemisphere.

The preferred environment for a marten is in a climax community conifer or mixed forest, however, they are highly adaptable to variety of differents forests. In the West, they are typically foud in spruce-fir forests where there is an abundance of prey species, particularly of the Clethrionomys (vole) genus. Martens studied in Ontario were found to inhabit forests of hemlock (Tsuga canadensis) (Chapman & Feldhamer, 1982). According to a US Forest Service study, martens succeed best in forests that have 40-60% canopy closure and tend to stay away from open fields (Snyder 1991). However, martens do not thrive in forests that are too dense, especially when there is no herbaceous growth (Snyder, 1991). Interestingly, it has been found that marten populations can survive small fires and selective logging and, in fact, may benefit from them (Snyder 1991). Shrub growth can produce environments friendly to small mammals and fruit, a primary source of a marten’s diet (Chapman & Feldhamer, 1982). Martens require forests that have complex physical structures near the forest floor because they provide the protection a marten needs, as well as an environment that is suitable for prey animals (Buskirk, 1998). Open fields near forests are often used as hunting grounds for martens, especially in the summer months, but only if they are near forest growth where the marten can hide quickly if needed (Kucera, et al., 1995). Ultimately, forest stands that have uneven aged growth are most beneficial because the vegetation is more diverse, proving the marten an abundant food base (Snyder, 1991).

As martens are solitary creatures, they prosper in more remote areas, away from human settlement. However, martens can become tame and trusting animals, if raised in captivity from a young age (Parker, 1990). It has been found that the marten’s home range is quite large for a mammal its size. In fact, Buskirk and Zielenski (1998) found that a marten’s range is 3-4 times the area typical of a terrestrial carnivore the same size, and over 30 times larger than a similar sized herbivore. This range, however, is largely based on the abundance of prey species and the types of prey available (Buskirk & Zielenski, 1998). It is obvious that martens are partial to forest environments because of access to prey, such as mice and voles, but also because the dense forests provide a place of protection and to make its den. Hollow logs, stumps, and trees make the best den for a marten. In trees, they typically will lay grass, moss, and leaves as bedding. They also will make their dens in squirrel burrows and logs on the ground (Chapman & Feldhamer, 1982). The US Forest Service says that forests covered with rotten logs and stumps were crucial in a marten’s selection of habitat (Snyder, 1991). Martens are just as adapted to cold winters as they are to summer. A marten will typically borrow under snow-covered logs or find stumps or empty crevices between piles of logs during winter to den (Spencer, 1987). Sometimes, a marten may move to lower elevations during winter, but this is dependent on human populations nearby (Nowak, 1991). However, most often, the marten will prefer to remain in the forest to forage through the snow. The marten is well adapted to digging and burrowing through the snow to reach logs, rock piles, and tree stumps looking for mammalian prey, which becomes the most prominent source of food during this time (Buskirk, 1998).

Economic Status/Human Impacts:

Even though martens have few natural predators, the biggest threat to their population is humans. Distributions of martens have remained relatively continuous from Labrador to Alaska, but the marten’s southern range, along the Great Lakes, and its range in Western United States have been rather fragmented due to human encroachment (Gibilisco 1994). Populations in the West have naturally been fragmented due to the varied terrain and discontinuous range of conifer forests. With an increase in humans entering forested regions and the use of the land for intense logging and human settlement, these naturally isolated populations have become further fragmented (Gibilisco 1994). Previous human settlement in the Great Lakes region has also, in the past, destroyed habitats of the marten and the fisher (M. pennanti) (Gibilisco 1994). Reintroductions strategies, as well as land management, have helped to mitigate some of these problems (Gibilisco 1994).

Martens are naturally curious animals and, so, are easy to trap (Chapman & Feldhamer 1982). Though not quite as valuable as the fur of a European sable (M. zebellina), the coat of a marten is quite popular in the North American fur trade. Because of their ease of capture, martens have been drastically over harvested (Chapman & Feldman 1982). In the 1810s, more than 140,000 martens annually were being harvested (Strickland 1994) and, by the mid 1850s, the Hudson’s Bay Company was harvesting, in Canada alone, 180,000 martens a year (Parker 1990). The fur market was virtually unregulated until the 1920s, by which time the American marten population was severely reduced. The 1920s saw protection laws introduced and, by the 1950s, annual marten harvest was down to 25,000 (Strickland 1994). With trapping of American martens cut down, teamed with reintroduction programs, the population sprang back. Ironically, by the 1980s, this increase in marten population, along with increased access to their habitat, and higher demand, the harvests rose back up to 192,000 annually, 75% of which was coming from Canada (Strickland 1994). Marten populations, already susceptible to fluctuations in small prey species populations and sometimes low reproductive levels, suffer greatly from trapping. Only current harvest management strategies and, most importantly, reduced popularity in fur products since the 1990s have kept trapping low and allowed populations to rise once more (Strickland 1994). It is the continued unpopularity of furs that will make the greatest impact on American marten populations in the future.

Bibliography

Anderson, E. 1994. “Evolution, Prehistoric Distribution, and Systematics of Martes.” In: Buskirk, S.W., A.S. Harestad, M.G. Raphael, & R.A. Powell, editors. Martens, Sables, and Fishers, Biology and Conservation. Ithaca & London: Cornell University Press.

Buskirk S.W., & W.J. Zielinski. 1998 (?) American marten (Martes americana) ecology and conservation. [Online] http://www.fs.fed.us/psw/rsl/projects/wild/zielinski/zielinski5.PDF [October 15, 2003]

Carr, S.M. 2000. “Distribution of American pine marten (Martes americana & M. Caurina)” [Online] http://www.mun.ca/biology/scarr/Martes_americana_vs_caurina.htm [November 8, 2003]

Chapman, J.A. & G.A. Feldhamer, editors. 1982. Wild Mammals of North America. Baltimore & London: John Hopkins University Press.

Colwell, L. (2003). "American Marten (Photo)". Larry Colwell's Main Page. Permission Granted. [Online] http://watermarkproductions.com

Gibilisco, C.J. 1994. “Distribution Dynamics of Modern Martes in North America.” In: Buskirk, S.W., A.S. Harestad, M.G. Raphael, & R.A. Powell, editors. Martens, Sables, and Fishers, Biology and Conservation. Ithaca & London: Cornell University Press

Kucera T.E., W.J. Zielinski, & R.H. Barrett. 1995 “Current Distribution of the American Marten, Martes Americana, in California”. California Fish and Game 81(3): 96-103. [Online] http://www.dfg.ca.gov/hcpb/info/bm_research/bm_pdfrpts/95_12.pdf [October 11, 2003]

MacDonald, D., editor. 1984. The Encyclopedia of Mammals: Volume 1. London: George Allen & Unwin.

MacDonald, D. 1992 The Velvet Claw, A Natural History of the Carnivores. London: BBC Books. Abstracted for www.bobpickett.org. [Online] http://www.bobpickett.org/velvet_claw.htm [October 11, 2003]

Marriot, J. 2003. "American Marten (Photo)" Wilderness Photography of Banff and Jasper National Park. Permission Granted. [Online] http://www.wildernessprints.com/. Photo obtained from Wildlife of the Rockies. [Online] http://raysweb.net/wildlife/pages/08.html.

Nowak, R.M. 1991. Walker’s Mammals of the World, Fifth Edition, Volume II. Baltimore & London: John Hopkins University Press.

Parker. S.P., editor. 1990. Grzimek’s Encyclopedia of Mammals: Volume 3.Translation of Grzimeks Enzyklopädie Säugetiere. New York: McGraw-Hill Publishing Co.

Powell, R.G. 1993. The Fisher, Second Edition. Minneapolis: University of Minnesota Press.

Pickett, B. 2003. “American Marten (Martes americana)” [Online] http://www.bobpickett.org/order_carnivora.htm#am [October 11, 2003]

Snyder, S.A., compiled for US Forest Service. April 1991. “Wildlife Species: Martes americana”. [Online] http://www.fs.fed.us/database/feis/animals/mammal/maam/all.htm [October 11, 2003]

Spencer, W.D. 1987. “Seasonal Rest-Site Preferences of Pine Martens In The Northern Sierra Nevada”. Journal of Wildlife Management. 51(3): 616-621.

Strickland, M. 1994. “Harvest Management of Fishers and American Martens”. In: Buskirk, S.W., A.S. Harestad, M.G. Raphael, & R.A. Powell, editors. Martens, Sables, and Fishers, Biology and Conservation. Ithaca & London: Cornell University Press.

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American martens belong to the order Carnivora. Over 65 million years ago, carnivores roamed the earth as squirrel-sized creatures that fed mostly on insects (MacDonald 1992). These ancestral animals led to the Miacids, who were the first mammals to develop flesh-shearing teeth called carnassials, a distinguishing characteristic of most modern carnivores (MacDonald 1992, Powell 1993). Those scissor-like teeth were used to shear through flesh and gave the carnivores an advantage over other mammals and eventually allowed them to become the dominant predators in the Northern Hemisphere by 20-30 million years ago (MacDonald 1992). Carnivores also developed a set of teeth to the rear of the carnassial teeth that allowed them to take advantage of other foods such as fruits and vegetables. It was this ability to diversify their diets that allowed the carnivores to continue their success (MacDonald 1992).
	Evolution of Order Carnivora, highlighting evolution of genus Martes (Powell, 1994).
In the late Eocene-early Miocene (34-40 mya), the Miacids evolved into two major groups, the Canoidea and Feloidea (Powell 1993). The latter branch diverged into the families Viverridea (civets), Felidae (cats), Hyaenidae (hyenas) and Herpestidae (mongooses) (MacDonald 1992). It is believed that the Mustelids (the weasel family, which includes martens) are descendents of the Canoidea family (Powell 1993). By the Miocene era, the four canoid families that are recognized today were distinguishable (Powell 1993): Canidae (dogs), Ursidae (bears), Procyonidae (raccoons) and Mustelidae (weasels) (MacDonald 1992). The fossil record is often difficult to discern regarding these early creatures, but it has been found that Mustelids diverged quickly from the remaining canoids, with the mustelids retaining the small, elongated bodies and the short, stocky legs with five toes that was a characteristic of the miacids (Powell 1993). Cooling of the world climate around 30 mya increased the world’s forests and allowed for the spread of Mustelids and other mammals. As this occurred, the Mustelids themselves began to diverge. Some Mustelids grew larger and evolved into modern day badgers and wolverines, while other groups retained a smaller and more tubular body in order to prey on burrowing animals (MacDonald 1992). By the Pliocene (2-7 mya), martens were a distinct group within the weasel family (MacDonald 1984). The fossil record is not complete for the Martes genus, because of their small body size and boreal forest habitat (Powell 1993). However, fossil records of extinct fishers (M. paleosinensis and M. anderssoni) have been found in China (from 4.8 mya) and the earliest martens were found in lower Miocene beds in Germany (Anderson 1994). Still large gaps exist and the first Pine martens (M. martes) were found to be in Central and Western Europe around 100,000 ka and, between 65-122,000 ka, the American marten crossed Beringia into North America (Anderson 1994). The population in North America first spread throughout the boreal forests of all of North American, then became isolated in the eastern United States by the Laurentide Ice Sheet, then reinvaded Western Canada and Alaska upon its retreat (Anderson 1994). A later migration from Siberia also occurred, bringing marten (extinct M. nobilis) populations to the Sierras and Rockies (Anderson 1994). Some research has shown that M. nobilis may simply be a larger ancestor to the current “caurina” (M. americana caurina) subspecies (Anderson 1994). As mentioned, the earliest martens appeared in Europe then spread quickly across temperate Asia and into North America. Today, there are three subgenera of marten, Pekania (fishers), Charronia (yellow-throated marten) and Martes (true martens) (Anderson 1994). The four boreal species of marten, M. martes, M. zebellina, M. melampus, and M. americana, replace each other geographically and have been referred to as a “superspecies” (Anderson 1994). However, because they all are similar in traits, behaviors, and habitat, some scientists feel that one day it may be discovered that these four species are shown to be one “circumboreal species” (Anderson 1994). The division of the American marten is under much debate. Some scientists argue as many as 14 different subspecies exist, while others feel many of those designations are merely arbitrary, and that there is more likely six different subspecies (Anderson 1994). The American marten has been distinguished into two subspecies groups, the “americana” and the “caurina”. These two groups are distinguished by several features including the shape of their skull, the auditory bullae, and the relative size of their upper molar (Anderson 1994). The “americana” group is typically associated with martens in Alaska, Canada, and the eastern United States. The “caurina” group, found in the western United States, such as the Sierras and Rockies, shows more similarities to the sable (M. zibellina) than to the “americana” group, and was the later migrant to North America (Anderson 1994). Research is also being done by some scientists who feel the American marten itself is not one, but two distinct species (M. americana and M. caurina) (Carr 2000). A distinction of two species, however, is still in debate.