Red Fox Evolution & Early Distribution

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Dogs and cats are Carnivorans, that is, they’re members of the taxonomic order Carnivora (note that this is different to simply being a carnivore, or meat-eater, which is not a taxonomic grouping), which is one of 29 orders within the class Mammalia. The evolution of carnivorans appears to have been a gradual process that happened in both North America and Eurasia, making it difficult to infer when it all started. Nonetheless, taxonomists (those who study how species are related to each other) currently think that the carnivorans evolved from animals called miacids, which were small tree-living mammals that looked similar to modern-day civets. At some point—by current thinking, around 42 million years ago (mya), during the mid-Eocene—it appears that the carnivorans split into the two groups, or suborders, that we recognise as cat-like (Feliformia) and dog-like (Caniformia). If, at this point, you’re wondering where mammals like mustelids, seals, bears, etc. fit in: they’re all dog-like carnivorans.

The evolutionary history of the dog family is still not completely resolved (and may never be, as new fossil finds and advancing molecular techniques offer new insights), but the following is a generally accepted hypothesis. Readers interested in a more detailed appraisal of dog evolution are directed to Xiaoming Wang and Richard Tedford’s authoritative account in their 2008 book Dogs: Their Fossil Relatives and Evolutionary History and I recommend the reader visits Wikipedia and The Searching Wolf. Briefly, the creature that taxonomists currently think gave rise to modern-day dogs was a medium-sized (about the size of a coyote) grassland predator of North America called Prohesperocyon wilsoni that appeared during the late Eocene, some 36 mya.

Artist impression of the small, slender-jawed fox-like canid Leptocyon, believed to be the ancestor of modern canids. - Credit: Noeliria / Wiki Prehistórico

The caniforms subsequently diverged into three lineages (which we call subfamilies): the Hesperocyoninae (‘western dogs’); the Borophaginae (‘bone-crushing dogs’); and the only one still around, the Caninae, which includes the dogs, wolves, foxes, etc. and is thought to stem from the now extinct small fox-like Leptocyon, which lived in North America. During the late Miocene, around 10 mya, something important happened: the third, and for our purposes most important, canid radiation began. This radiation was probably in response to a vacant niche opening up as the borophagines started to die-out, and not only marked the birth of all the dog species we know today but also heralded the appearance of three modern-day genera in the south-western USA: Canis (dogs, wolves, dingoes, etc.); Urocyon (Gray foxes); and Vulpes (true foxes). In essence, it was around 10 mya that the fox lineage split from the wolf-dog lineage. A couple of million years later the dogs started arriving in Eurasia, and the Pliocene (4-5 mya) saw the dogs spread into Africa and South America. Around six mya, the first wolf-like dog arrived in western Europe.

According to Wang and Tedford, the first true foxes appeared in North America late in the Miocene (around 9 mya) and were represented by a small Californian species, known as Vulpes kernensis, and a larger species (V. stenognathus) that was found throughout the continent. Foxes spread out from North America, presumably via the Bering land bridge, and colonised Europe. The oldest Old World fox specimen so far identified is V. riffautae, which was found in the Central African country of Chad and dates to the late Miocene (some 7 mya). Recent work by Louis de Bonis and colleagues at the Université de Poitiers in France has suggested that the foxes and other canids first spread throughout Africa, before invading Europe via a trans-Mediterranean route towards the end of the Miocene. There is then something of a hiatus in the vulpine fossil record until the early Pliocene (about 4 mya), with foxes from China and Turkey among the earliest Eurasian specimens.

The origins of our modern-day Red fox (V. vulpes) is equivocal, although most authors agree that it is descended from the Vulpes alopecoides, which lived in southern Europe at the end of the Pliocene, around 2.6 mya – fossil remains of this species was first discovered in deposits from Italy during the late 1800s, and remains have subsequently been found in France, Spain and Greece. A competing theory is that modern Red foxes evolved from the Chinese fox V. chikushanensis. Whatever the ancestor, in his 1968 book Pleistocene mammals of Europe, Björn Kurtén notes that early Red foxes were likely to have been smaller than modern ones, based on the observation that fossil remains of early foxes are smaller than those of present-day animals.

In their 1982 comparison of Red and Arctic (V. lagopus) fox ecology, Pall Hersteinsson and David Macdonald note that both species are descendants of V. alopecoides and that the two species diverged during the Pleistocene. Indeed, the earliest fossil evidence for V. vulpes comes from the Old World, dating to the early Pleistocene (about 1.8 mya) of Hungary, and in her 2008 study of Red fox dentition Polish Academy of Sciences mammologist Elwira Szuma suggested that the current V. vulpes line evolved either in Asia Minor or North Africa around this time. During the Pleistocene, Europe underwent a series of cyclical glacial periods and this waxing and waning of ice had profound effects on the mammal populations on the continent.

Until recently, we thought that the advancing ice sheets forced foxes south, into warmer parts of what is now Iberia, Italy and the Balklands, from which they spread back out from as the ice retreated - this is known as the glacial refugia hypothesis. Genetic work by Amber Teacher and colleagues at the University of London published in 2011, however, suggests a different story. Teacher and her co-workers analysed DNA samples from 165 Red foxes, from across Britain and Europe, held in museum and university collections and found very little genetic drift. Normally, if the fox population was fragmented into small pockets separated by the ice, we would expect to see inbreeding and the populations would start to diverge from each other genetically (i.e. 'drift' genetically). Instead, these data suggest that foxes toughed out the glaciations as a single, large interbreeding population. Genetic data published by Ceiridwen Edwards, at Trinity College in Dublin (Ireland), and colleagues in 2012 supported Teacher's findings, and it is now generally accepted that foxes weren't restricted to these refugia during the last glaciation.

A Red fox (Vulpes vulpes) in North America. Genetic data suggest foxes group broadly into a Holarctic clade in North America and Europe and a Nearctic clade found only in the United States. - Credit: Jane Hendrix

Previously it was believed that the first modern Red foxes (i.e. V. vulpes) to appear in the New World migrated (again, presumably across the Bering land bridge) from Europe at the end of the Pleistocene (around 1 mya) and, from here, Red and Arctic foxes colonised much of North America. Recent genetic work by Keith Aubry and his colleagues at the Pacific Northwest Research Station in Washington, however, has revealed new information on the spread of the Red fox in North America. Aubry’s data suggest that this species first reached North America during the Illinoian glaciation that lasted from roughly 300,000 to 130,000 years ago; during the next 30,000 years (the Sangamon interglacial period) the foxes spread south from Alaska, across what is now the contiguous USA.

The large ice sheet that covered most of Canada and the northern fringes of the USA from around 100,000 to 10,000 years ago (during the Wisconsin glaciation) kept the Red foxes in Alaska (the population of which was added to by a more colonisers arriving from Eurasia) separate from those in the southern USA. So, the result was two isolated populations (or clades): one in Alaska (Holarctic clade) and one in the south (Nearctic clade). When the ice melted the Holarctic clade spread south and east, while the Nearctic clade spread north, the two meeting in central Canada. Aubry’s data reveal more than just the distribution of foxes in pre-history, it also elucidates the relatedness of the animals currently inhabiting North America (see: Taxonomy).

Whatever the ice sheets did to their distribution, fossil evidence suggests that the modern Red fox has been in North Africa for the last 700,000 years and Europe for at least the last 400,000 years. It is worth bearing in mind that fossil are likely offer conservative dates of first appearance. Indeed, in a paper to the journal Organisms, Diversity and Evolution at the end of 2015, a team of Portuguese geneticists, led by João Leite at the Universidade do Porto, present data suggesting that the Rüppell's fox (Vulpes ruppellii) split from North American Red foxes about 1.25 mya (i.e. Rüppell's fox is the Red fox's closest living relative), implying that Vulpes vulpes was in the region much earlier than the fossil evidence intimates. The genetic data interrogated by Leite and his colleagues also show a split between the red foxes in the Mediterranean Basin; one group in North Africa (to which Rüppell's fox is closely allied) and a second in Eurasia (to which, interestingly, Egyptian specimens were closely allied).

In Britain, remains of the Red fox have been found in Wolstonian Glacial sediments from Warwickshire, suggesting that they were around between 330,000 and 135,000 years ago. We also have fossil remains dating back to the Pleni-Glacial in England, as long as 75,000 years ago, and Red fox remains have been found in Kents Cavern in Devon (UK) that date to around 23,600 BP, suggesting foxes were in Britain just before the period of maximum cooling during the last glacial maximum. Following the retreat of ice from the last ice age (the Late Glacial) some 15,000 years ago, fossil evidence shows many of the larger mammal species beginning to re-appear in Europe and extend their range northwards. Red fox remains reappear in the German fossil record around 14,000 BP and from at least one site in southwestern France around 13,500 years ago alongside Artic fox and bison remains.

According to Derek Yalden’s fascinating book, The History of British Mammals, post-glacial remains of the Red fox have been found at several sites around Britain and suggest that this species re-appeared ‘naturally’ (i.e. without any obvious assistance from humans) around 10,000 years ago. Indeed, other fossil data imply that the ice forced foxes into the warmer southern regions of Europe (e.g. Iberia, Italy, southern France, etc.) for only a (geologically) brief period, after which they quickly returned to central Europe and Britain; at the time, the UK was connected to the European continent. The flooding of the Doggerland “bridge” around 6,500 years ago isolated Britain’s foxes from those in Europe, putting an end to any natural mixing of the populations.