Red Fox Taxonomy

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Many texts on fox natural history cannot help but draw comparisons between the fox and the cat and, if you spend any time watching them, you’re certainly struck by how similarly they behave: both have the same delicate, tripping gait; both stalk and pounce in much the same way; both sit and sleep with tails curled around their bodies; both twitch tail tips to allow young to practice hunting; both will use a paw to scoop unwary fish out of a garden pond. Anatomically, however, foxes have the large ears, the long pointed muzzle, the 42 teeth and the non-retractable claws (five on forefeet and four on hind) that we typically associate with dogs, although they do share the vertically-slit pupils commonly associated with cats (larger canids, such as wolves and domestic dogs, have round pupils). Red foxes are the largest member of the fox family and among the most specialised for a carnivorous diet. In the second volume of their Mammals of the Soviet Union, V.P. Heptner and N.P. Naumov note that their facial area is more well developed, with their skulls exhibiting fewer neotenous traits than other fox species.

Despite the resemblance, foxes are dogs not cats; the feline similarities are a result of convergent evolution, where two species look similar because they occupy a similar ecological niche and/or habitat. (Sharks and dolphins provide a good example of convergent evolution. They look very similar but aren’t related. They have evolved the same basic body shape because it works very well in aquatic habitats).

The origin of Vulpes

The cover of Linnaeus' 10th volume of Systema Naturæ, published in 1758. In it, he described the Red fox as Canis vulpes. - Credit: WikiMedia Commons

Foxes have been a well-known part of our countryside for many centuries (see: Interaction with Humans), but Swedish scientist and father of modern-day taxonomy, Carl von Linne (often known simply by his pre-ennoblement surname, Linnaeus), was the first to formally describe and classify the Red fox in the 10th edition of his Systema Naturæ, published in 1758. Based on a specimen from Uppsala, the university town of south-east Sweden in which he studied, Linnaeus gave the animal the Latin name Canis vulpes (meaning literally ‘dog fox’), recognising its place within the dog family. The principal idea behind classifying animals is to illustrate their relatedness, so closely related species are grouped together (in the same genus, for example), while more distantly related ones sit further away. As was the case with much early taxonomy, as more species were described and interrelationships became better understood the initial groupings proposed by Linnaeus for the dogs soon became too restrictive to adequately reflect their diversity; this led to the creation of new genera within the dog family (Canidae). One such genus is the one we now use for most of the modern-day foxes: Vulpes.

Until very recently, the creation of the genus Vulpes was credited to German zoologist Just Leopold Frisch. In 1775, Frisch published his thesis on the ‘systematic table of four-footed animals’ in which he curiously described the ‘common fox’ as both Vulpes vulgaris (vulgaris meaning ‘common’ in Latin) and Vulpes crucifer (confusingly, both names referred to the same animal). Following Frisch’s lead, Vulpes was used by many subsequent authors when referring to the Red fox. Indeed, since about 1900 there has been almost universal reference to Vulpes vulpes, rather than Canis vulpes. Unfortunately for Frisch, he didn’t follow the taxonomic rules and so, in 1954, the ruling body on such matters (the International Commission on Zoological Nomenclature, or ICZN for short) rejected his work, which meant that it couldn’t be used by taxonomists.

Not everyone was happy with the ICZN’s stance, arguing that it was confusing. Fortunately, the ICZN revoked their initial ruling in August 1979, almost five years after Juliet Clutton-Brock and Gorbon Corbet (both mammologists at London’s Natural History Museum) submitted a proposal to them arguing that the name Vulpes was recognised throughout the world (and had been since the start of the twentieth century) and that it was more important to be consistent in our naming than it was to strictly follow the rulebook. In other words, for the last 75 years people have been using Vulpes to refer to foxes and it’ll confuse the heck out of them if we now say they can’t use that and need to use Canis instead.

The ICZN didn’t entirely agree with this argument, but decided that Vulpes was such a well-known name that an exception was justified. So, most (although, as we shall see, not all) taxonomists returned to using “Vulpes Frisch, 1775” as the genus for most members of the fox group. In 2008, however, Francisco Welter-Schultes and Rebecca Klug at the Zoologisches Institut der Universität in Germany discovered an almost unknown early work on animal and plant taxonomy by French naturalist François Alexandre Pierre de Garsault, which he published in 1764. In this volume, Garsault used the genus Vulpes without a species, but accompanied it with a drawing of a Red fox. In taxonomic circles there is a rule of preference saying that the earliest valid name or reference has priority and, as Garsault used Vulpes in the same sense as, but 11 years earlier than, Frisch, he gets the nomenclatural credit. In other words, Garsault is credited as the first person to use (the ‘inventor of’, if you like) the genus Vulpes for foxes and authors using “Vulpes Frisch, 1775” need to amend the reference to say “Vulpes Garsault, 1764” instead.

From Canis to Vulpes

The precise point at which the Red fox was first placed in the Vulpes genus seems to have been lost in antiquity, but many early nineteenth century writers used Vulpes as a subgenus within Canis—so the Red fox was referred to as Canis Vulpes vulpes—and this continued until relatively recently. By the 1820s, British zoologist John E. Gray was using Vulpes as a genus and, in their 1832 Symbolae Physicae Mammalia, German naturalists Wilhelm F. Hemprich and Christian G. Ehrenberg recognised that the foxes could be grouped apart from the wolves and proposed the Vulpini (a taxonomic grouping called a tribe, that sits between the family and genus level) for them. In 1846, writing in the first volume of their Viviparous Quadrupeds of North America, John J. Audborn and the Rev. John Bachman grudgingly elevated Vulpes from subgeneric to generic level, spurred on by the sheer number of species already held within Canis:

The characters of this genus differ so slightly from those of the genus CANIS, that we were induced to pause before removing it from the subgenus in which it had so long remained. As a general rule, we are obliged to admit that a large fox is a wolf, and a small wolf may be termed a fox. So inconveniently large, however, is the list of species in the old genus CANIS, that it is, we think, advisable to separate into distinct groups, such species as possess any characters different from the true Wolves.

The Vulpes genus contains 12 species that include animals adapted to a variety of environments, including the Corsac fox (Vulpes corsac). This species is a specialist of grassland and semi-desert areas in its native range of Asia. - Credit: Anne-Marie Klaus

The characters Audborn and Bachman were referring to, that separate the foxes from wolves, include the pointed muzzle, vertically-slit pupils, only slightly curved incisor teeth, slender form, relatively shorter legs and long, thick, bushy tail. Various taxonomic arrangements were subsequently proposed, some following Audborn and Bachman’s decision and others opting to either ignore Vulpes, or relegate it to subgeneric status. It would be 34 years, however, before a significant attempt at arranging the members of the Canidae was published.

Driven by his disillusion with previous attempts to classify the members of the dog family, the great London-born physiologist, and evangelical evolutionist, Thomas Huxley published his detailed study on the classification of the Canidae in the Proceedings of the Zoological Society of London during August 1880.

In this magnum opus, Huxley divided the canids into two groups based on various cranial and dental characteristics: the Alopecoids (true foxes) and the Thooids (hunting dogs, wolves, and South American foxes that are currently assigned to the Lycalopex genus). Huxley, however, retained the Red fox as Canis vulpes. Nonetheless, the late 1880s represent the point at which canid classification stabilised; at this point we had most of the species that we currently consider to be members of the Canidae.

Following Huxley’s scheme, Canis and Vulpes were variously used when referring to the Red fox and some, Clarence L. Herrick in his 1892 Mammals of Minnesota for example, were still using Frisch’s specific name vulgaris (i.e. Vulpes vulgaris), rather than vulpes. By 1912, however, Gerrit Miller had adopted Vulpes vulpes in his ‘Catalogue of the Mammals of Western Europe’ and, in 1945, Simroe Foundation mammologist George G. Simpson published his classification of mammals in which he split the dogs into three subfamilies, with all the living species placed into the Caninae. Simpson recognised Vulpes as a genus within the Caninae, but noted how:

…the recent canines are quite uniform in structure, and it would be justified from many points of view to unite them all in a single genus.

We then had Clutton-Brock and Corbet’s argument to the ICZN and the eventual ruling in 1979. Just before this ruling (in April 1978), however, American Museum of Natural History curator Richard Van Gelder agreed with Simpson’s 1945 concerns and relegated Vulpes to a subgenus within Canis once more. Nonetheless, the ICZN has the final say on these matters and, under their Opinion 1129 (1979), it was ruled that Vulpes vulpes is the valid name for the European Red fox. In order for a taxonomic group to be considered valid it needs to contain all the descendants of a common ancestor (we call this a monophyletic group); if it doesn’t (i.e. it’s missing some, or has ‘extras’) it’s considered invalid, or paraphyletic. Overall, it seems that the ICZN made the right decision and recent molecular studies have shown that Canis is paraphyletic. There has been much work recently using different genetic markers to assess relatedness among the Canidae and each has proposed slightly different arrangements. To avoid dragging this section on unnecessarily, I won’t go into the details of them here.

The current situation is that the Canidae contains 36 species that can be divided into two broad groups (Tribes): the Vulpini, which contains the fox-like canids; and the Canini, which contains the dog/wolf-like canids. It is the Vulpini that interest us here and this tribe contains three genera: Otocyon (Bat-eared fox); Nyctereutes (Raccoon dog); and Vulpes (true foxes). The six species of South American fox (Lycalopex) and the Crab-eating fox (Cerdocyon thous) are grouped within the Canini. It seems that the red fox group is only monophyletic if it includes two species that were previously split out: the Arctic fox (Alopex lagopus) and the Fennec fox (Fennecus zerda). Thus, it is now widely accepted that these species are Vulpes lagopus and Vulpes zerda respectively, and this brings the number of species currently held within the Vulpes genus to 12. Some authors have suggested that Vulpes is paraphyletic unless it contains Nyctereutes, but a study published in the journal Molecular Biology Reports in 2011 found no support for this, placing the Raccoon dog and the true foxes as sister groups (i.e. more closely related to each other than to any other group).

The Red fox shows what we call biological plasticity – in other words, they’re capable of adapting their form to handle different environments. The result is that Red foxes living in different parts of the world can look significantly different to each other. Consequently, there are currently 48 proposed subspecies of Vulpes vulpes, based on differences in size, skeleton, teeth, colour, etc. No doubt some of these populations have been separated for long enough to make some of the subspecies valid, but it is very difficult to establish which they are and it seems very unlikely that all 48 are valid. Indeed, Anthony Mitchell-Jones and his co-workers were skeptical about the number of proposed European subspecies and, in their 2002 Atlas of European Mammals, considered a maximum of five—more likely four—to have any true validity.

Another member of the Vulpes genus, the Fennec fox (Vulpes zerda), is a desert specialist, native to the Sahara of North Africa. - Credit: Andrew Bertram

Using a small sample of foxes collected from across the Northern Hemisphere, Paolo Cavallini found that he could divide them into three groups based on size. In his 1995 paper to the journal Annales Zoologici Fennici, Cavallini explained:

Red foxes from North America are comparatively light, rather long for their mass and with a high sexual dimorphism. British foxes are heavy but relatively short, whereas European foxes are closer to the general average among populations…

Cavallini goes on to note that British foxes were more similar to European animals than to those in North America; his sample was relatively small (20 populations), but the data certainly suggest a separation is warranted and further, larger scale, studies should prove rewarding. Cavallini was not the only person to see such a difference between foxes on different continents and, although most biologists lump British and European foxes together, some recognise a distinction between Eurasian and North American foxes; the two are often considered different subspecies and recent genetic work suggests that are probably different species.

North American Red foxes

A North American Red fox in the snow. Genetic data suggest some North American fox populations warrant at least subspecific recognition and some may be species in their own right. - Credit: Marshall Hull

Early naturalists described several species of Red fox from North America based on differences in size, colour, skull dimensions and geographical range. By the end of the eighteenth century, however, most of these had been synonymised with (considered to be ‘types’ of) the widespread American Red fox, Vulpes fulva (fulvus is Latin for ‘reddish-yellow’ or ‘tawny’). A study, during the late 1950s, of the pelts and skulls of foxes collected in the US and compared to those from Eurasia found a general ‘cline’ in the foxes, concluding that the American fox isn’t a distinct species; instead it is a race/subspecies of the Eurasian fox.

Most of the genetic work to-date suggests that there are two major ‘groupings’ (or clades) of foxes in North America: foxes in Alaska and western Canada group together with those from Eurasia to form a Holarctic clade, while those in some southern and eastern states form a second, genetically-distinct, Nearctic clade that is made up of animals unique to North America. At some point during the Wisconsin glaciation, the suggestion is that the Nearctic clade split into two subclades; one in the east and one in the west. When the ice melted, around 10,000 years ago, foxes in the east (the eastern subclade) followed the boreal forests north and colonised eastern and central Canada. Foxes in the west (mountain subclade), however, colonised the alpine meadows and subalpine parklands of the high western mountains. It seems that the mountain foxes are better adapted to the cold, harsh conditions at high altitude and do not mix with foxes from low elevations. In Yellowstone, for example, Bob Fuhrmann has found foxes living above 2,100m (6,900ft) to be genetically different to (and don’t mix with) those below this altitude - they also appear to be slightly larger, have smaller ears, paler fur and prefer more open habitats than those living below 2,100m.

Early European settlers released Red foxes—transported from Britain, France and Scandinavia—along the eastern seaboard (i.e. the eastern coast of the USA, from Maine in the north to Florida in the south) for hunting purposes as early as the mid-1700s. The most recent genetic studies suggest that some of these imports established populations and bred with indigenous animals and these 'Anglo-American' hybrids are still present in human-dominated landscapes of the east coast. More widely, however, North America does appear to have two very distinct lineages of Red fox: foxes in Alaska and Western Canada that split from those in Eurasia relatively recently (~50,000 BP); and those in the Western mountains of the US, Sacramento Valley, California, and Eastern Canada/US that are much older, originating during the Illinoisan glaciation (300-500,000 BP). The genetic analyses certainly appear to support the taxonomic separation of at least some of North America's foxes from those in Europe and Asia. (For a more detailed appraisal of this subject, please see the QA)

British Red foxes

The subspecies Vulpes vulpes crucigera was described from Germany by naturalist Johann Bechstein in 1789. This subspecies, which was noticeably smaller than the one Linnaeus described from Sweden 31 years earlier (the ‘type’ specimen), had noticeably different teeth—they were smaller, with widely spaced premolars that had obsolete or absent secondary cusps—and a brighter yellowy-red coat than the type specimen. In his 1912 Catalogue of the Mammals of Western Europe, former United States National Museum curator of mammals Gerrit Miller Jr agreed with Bechstein that this was a valid subspecies—one of three found in Europe—and gave its range as central and southern Europe, from Ireland east to Greece.

There has been much debate about whether it is really possible to lump foxes from particular areas together and whether tooth size and spacing is actually too variable among foxes to offer evidence of taxonomic separation. Releases of foxes imported from Europe in Britain during the 17th Century and the interbreeding that almost certainly occurred between them and indigenous stock further weakens the argument for separation. Indeed, it is rare to find post-1980 authors who consider crucigera to be a valid subspecies. There are some genetic data, particularly from foxes in the Mediterranean, that suggest distinct groups do exist and that there may be a case for assigning some subspecies, but the data simply don’t exist for a sufficiently large geographical area to be certain whether similar groupings can be applied to other Eurasian populations.

The Red fox found in Britain is sometimes assigned to the subspecies crucigera, although not all authorities are convinced. Britain has a rich history of fox imports, which seem to have diluted the gene pool. - Credit: Peter Trimming

Ceiridwen Edwards at the Smufit Institute of Genetics in Dublin and colleagues looked at 399 modern and 31 ancient (fossil) samples of fox DNA from across Europe and found a high degree of phylogeographic structuring across the continent. Their data suggest British foxes are derived from central European populations that became isolated after of the closure of the land bridge with Europe. The geneticists found that although British foxes had clearly diverged from mainland populations, the main gene sets (haplotypes) that British foxes had were also found in Central European populations (i.e. foxes in France, Switzerland and Luxembourg) suggesting that, prior to the formation of the English Channel (the submersion of the Doggerland Bridge) some 8,500 years ago, these northern European foxes formed a single, inter-mixing population.

The most notable finding of Edwards and her team was the division between foxes in most of Europe and those in Britain, Ireland and Holland. The theory is that gene flow between foxes in Britain and the rest of Europe became restricted as the English Channel began to form, but continued between foxes in Britain and Holland right up until the UK was completely cut off. A study published in the journal BMC Evolutionary Biology the previous year, by contrast, also looked at DNA samples from modern and ancient Red foxes from across Britain and Europe and found no clustering of any sort, and strikingly little apparent change in population size over time. The authors concluded that:

It is probable that the high dispersal ability and adaptability of the red fox has contributed to the lack of observable differentiation, which appears to have remained consistent over tens of thousands of years.”

In other words, rather than foxes being split into small groups in ice-free regions (so-called ‘refugia’) at the last glacial maxima (which could, through inbreeding, allow the build-up of unique genetic traits that make each population different from another), the population was pushed back as one large interbreeding group. Indeed, in their 2015 paper to the journal Mammal Research, Food and Environmental Research Agency biologist Helen Atterby and her colleagues presented their genetic analysis of 501 foxes collected from around the UK and from two populations in France.

Their data show that there’s generally very little structuring in the British fox population, suggesting foxes move around and breed freely. Using a couple of genetic modelling techniques, they did find support for four broad groups, including foxes from Sussex and Kent clustering with those in Calais in northern France. This provides genetic support for the reports by early authors such as Dixon and Bovill that foxes were introduced to Britain from the continent, with France being a prominent sourcing site. Atterby and her coworkers suggest that, as the foxes were imported largely to be hunted, they may not have survived to breed and this may explain why continental genotypes aren’t more widespread in Britain today.

In the end, the jury is still out, but the majority of biologists now generally consider that Vulpes vulpes is just a highly variable species that ranges throughout Europe and Asia and do not attempt to categorize it further. (For more information, please see the associated QA)

Urbanites: A different species?

Finally, there has been some suggestion that urban and rural foxes may be separate subspecies. To date, I know of no evidence in support of this. Indeed, radio-tracking studies by several teams have shown that urban and rural foxes can and do mix. The data do, however, paint a mixed picture, with some animals dispersing out of one town, crossing several kilometres of potentially suitable rural habitat, to settle in a neighbouring town; others have dispersed from rural areas into towns and cities, while some have done the opposite. The Bristol University team are quick to point out that there can even be very short-term visits; rural individuals have been tracked entering neighbouring urban areas at night to hunt.

In a 2003 paper to the journal Molecular Ecology, a team of scientists from the Zoological Society of London and University of Zurich published their data on the foxes living in the Swiss city of Zurich. The researchers found that, although urban foxes appeared to breed most often with other urban animals (unsurprising, given their social system), urban and rural animals also interbreed. Indeed, the authors wrote:

Currently observed levels of migration between urban and rural populations will probably erode genetic differentiation [between urban and rural populations] over time.”

In a paper to the Journal of Zoology in February 2017, a team of biologists at Hokkaido University reported that, based on genetic data, foxes living in the northern Japanese city of Sapporo grouped into three distinct 'subpopulations'. There was weak gene flow between the groups, suggesting some movement of animals between the subpopulations took place, but generally fox dispersal appeared to be limited by the presence of the Toyohira River and JR Hakodate Line Railway. The smaller Ishikari River and quieter JR Gakuentoshi Line Railway (140 vs. 57 trains per day), by contrast, had no discernible impact on gene flow. This serves as a reminder that different fox populations behave differently and we should be cautious about drawing too many conclusions from limited data.

The phenomenon of the "urban fox" is well established in Britain, but city foxes are the same species as those in our countryside and urban foxes may hunt in rural suburbs at night while country foxes may venture into villages for a meal. The rural-urban boundary is much more a human concept that a fox understanding. - Credit: Paul Cecil

In the UK, the fox population is heterogenous and a recent study found a high proportion of genetic mixing among populations from across the country. In a paper to the journal Mammal Research in 2015, a team led by Graham Smith at the Food and Environment Research Agency (FERA) in York present the results of their genetic study on foxes collected as part of a UK-wide programme monitoring for the parasitic nematode Trichinella. Overall, the biologists found that populations varied by only just over 5%, suggesting that the British fox population is, genetically-speaking, well-mixed.

The results do lend some support to foxes from East Anglia (Norfolk, Suffolk and Essex) clustering together, and those from southern Scotland and northern England also being more closely allied to one another than to foxes elsewhere in Britain. When comparing urban (Leicester and London) data sets, there was some support for these foxes being distinguishable from rural animals, suggesting reduced gene flow between urban and rural populations, but, as with the Zurich study, the differentiation was very low. Interestingly, foxes from Sussex and Kent seemed to group closely with those from Calais, supporting historical records of foxes being imported into Britain when numbers ran low (see Distribution and Introductions).

Taken in concert, the genetic data we currently have suggest the ability of the fox to adapt to a broad range of different habitat types, and the high dispersal rates and distances seen in many populations means there is no significant barriers in gene flow. Consequently, the Palaearctic Red fox is classified as follows:

Kingdom: Animalia (Animals)
Phylum: Chordata (Possess a basic 'backbone')
Class: Mammalia (Mammals)
Order: Carnivora (Possess carnassial teeth)
Family: Canidae (Dogs)*
Tribe: Vulpini (Fox-like canids)
Genus: Vulpes (from Latin meaning 'fox')
Species: vulpes (increasing evidence suggesting some isolated North American populations are fulva)

Note: Some authors place foxes within their own subfamily: the Vulpinae. Here, however, I am following Ingi Agnarsson, Matjaz Kuntner and Laura May-Collado’s 2010 phylogeny of the Carnivora.

For more information on how species are classified see: Taxonomy.