Late afternoon sunlight floods the back of my house, rendering the wide first floor landing a luminously golden Byzantine capsule, bathed in light-shafts of ruby, emerald and sapphire from the old Edwardian stained-glass window. I do much of my writing on that landing, enjoying the interplay of light and colour. Where I go, my dog goes. The little terrier likes to doze beside me, sometimes twitching or barking in his sleep. I often wonder what dogs dream about: is it the parklands and mountains, where every rabbit is fair game, or does some other kind of ancient memory, carried in the mitochondria from generation to generation, whisper to even the littlest dog when they rest beside us, of a time when dogs were fearsome wolves.
I’d recently been reading the delightful research of Hulme-Beaman and Larson on the domestication of the dog. It got me thinking about some of the now-extinct canines of the Pleistocene, such as Xenocyon – that great mystery canid of the Pleistocene. There’s continued debate about what genus Xenocyon actually fits into: many consider it to be a canid, while others classify both X. falconeri and the earlier X. lycanoides to be the true ancestor of today’s ferocious yet beautiful African Hunting Dog, Lycaon pictus.
It may be that our understanding of the genus Canis is a little too simplistic, and needs a little revision to include creatures such as Cynotherium, Lycaon and of course Xenocyon, which in appearance was likely somewhere between a hyena and a wolf. Weighing between 30 and 40 kg, with a wide and broad head, Xenocyon was not to be messed with. The fangs alone indicated a robust, hypercarnivorous creature roughly the size of a wolf, perhaps a bit bigger in some cases, and a superb predator. If they were indeed the ancestors of the African Hunting Dog, then their hunting pack techniques would have been savage, relentless – and successful. Sadly, we don’t know if these muscular dogs were beautifully speckled and painted like L. pictus, or if they had coats of one colour, more akin to a wolf or dhole.
It is not surprising these canids reached pretty much the top of the food-chain and were found across Eurasia, Europe and even North America during the Mid-Pleistocene. Fossils have been found as far east as Japan, at the Tama River just outside Tokyo, with specimens also found at Westbury in Britain. However, more plentiful fossils have been found in Untermassefeld in Germany and across Italy and Spain. There are even a few specimens in North America, although some believe they never quite got a grip on the landscape due to competition from the larger and heavier Canis dirus.
So, how did Xenocyon spp manage to be so widespread that they ruled Europe and Eurasia with a paw of iron? Well, most of it is probably due to climate fluctuations on the boundary of the Pliocene and Pleistocene Epochs. We know now that there have been regular periods of glaciation, thaws and reglaciation, long before humans came and made it ten times worse with carbon emissions. The beginnings of the Palaeolithic period are often placed around 1.7 million years ago, when hominids such as Homo erectus were striding out across Africa seeking new vistas. They were not the only ones. Another species of predator was also on the move, in a bio-event known rather catchily as the ‘Wolf Event’. Dogs went walkies from Africa to Eurasia and further.
These periods of intercontinental migration usually occur due to climate changes and the Wolf Event is probably no different (another example of course is the Great American Biotic Interchange, when northern megafauna crossed the land bridge at Panama to access south America). Sometimes Xenocyon is referred to as the African Wolf, as there certainly was movement of the earliest species, X. lycaonoides, from Africa around the same time as other great predators following the movements of herd animals. Nothing remains static in environmental histories. Temperatures in Europe were cooling, starting the story of glaciation and extinction we now call the Ice Age. Herds of herbivorous creatures would follow availability of good grazing, and right behind them would be the hunters, looking for juicy antelopes and equids. In the case of the packs of Xenocyon, they most likely would have welcomed a juicy H. erectus into their a la carte menu, as hominids would have been relatively defenceless against packs of creatures who hunted like African Dogs.
At any rate, the Wolf Event started a major dispersal of predators which was followed around 0.9 million years ago by what’s not so-catchily named the ‘end-Villafranchian’ event, which created a rejuvenation of fauna. Just for a wee while, the climate improved before the onset of the glaciers. The hypercarnivores, of course, were not as dependant on temperature fluctuations or their physical environment for survival – they depended on that age-old interaction, the balance between predator and prey. As long as there were herds of tasty meals on hooves, they could manage.
As the last Ice Age gripped the Northern Hemisphere, herbivores retreated to refugia, vegetation died, and extinctions occurred, many of course which are documented here on Twilight Beasts. Sometimes humans were involved in extinctions, other times not. In the case of Xenocyon, it is unlikely that humans were responsible – this is one we get off the hook for. In fact, we really don’t have an accurate timeline for their absolute extinction, though it’s mostly considered they were extinct by around 125,000 years ago. Fossil assemblages of the wild dog were found at Venta Micena, in south-eastern Spain in 1995, and one of the prize catches of this collection was a well-preserved skull. It gave a very good image of those savage canine teeth, the bone-crushing weight of the animals’ jaws and the sheer power of the animal. However, further examination of it, and other skulls, showed a lack of symmetry in the shape of the heads. The conclusions have been surprising – it’s likely the abnormalities of jaw and general conformation were due to genetic homozygosity. This is when an organism has two identical forms of a particular gene, with the same one inherited from each parent: The demise of Xenocyon may very likely have been down to faulty genetics, possibly caused by inbreeding. The fact that the creatures survived beyond puppyhood was also remarkable, indicating the same sort of co-operation and pack behaviour shown by extant Lycaon pictus to encourage the vulnerable to feed first from the softest tissue of the felled prey.
So, to some extent, Xenocyon populations became unstable and short-lived due to small breeding groups and genetic disorders of increasing severity – though it may not be the whole story. Many consider that Cynotherium sardous, a small canid of Pleistocene Sardinia, could well have been the descendant of Xenocyon – though C. sardous is a story for another day. Remember that islands do odd things to species trapped on them – either gigantism or dwarfism, depending on the environmental stresses. The restriction of life on an island reduced the size of the earlier Pleistocene canid resulting in adaptation to an insular environment, with smaller prey, such as Pleistocene bunnies which required a different way of hunting, far removed from roaming vast expanses of grassland and savannah.
Considering that at least on one occasion, Xenocyon contributed to the creation of a different canid, we can revisit the delicious research carried out by numerous geneticists such as Wayne, Larson and Hulme-Beaman, whose collective findings were recently published in Science journal. The conclusion most geneticists are reaching is that all varieties of modern dogs can trace their ancestry to extinct wolf-like creatures. Random interbreeding, environmental changes and then human involvement in selective breeding for specific qualities means that nature just doesn’t stop dead. What we perhaps have thought of as outright extinction sometimes is really just evolution doin’ its thing- changing and adapting until new responses are needed to new environmental challenges.
We still don’t know what ancestral memory whispers to our pups as they slumber, but I like to think that when they sleep, there’s a waft of an ancient savannah breeze, with the scent of a Pleistocene herbivore on that wind, and our little ones get to run with those wonderful twilight dogs who eventually would become our best friends.
Written by Rena Maguire (@JustRena)
An explanation of homozygosity here
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