The ice ages were a series of major glaciations with intervening interglacials. This process has been playing out over about two and a half million years. The epoch over which this all occurred is the Pleistocene.
The last glaciation finished about 11,500 years ago. Our present epoch has been given a new name, the Holocene, which implies that this is something different not just another interglacial. We shall see.
Prior to the Pleistocene the world was a warmer place. This was the Pliocene an epoch that spanned about 9 million years. In mid-Pliocene temperatures were 2 or 3°C warmer than present , sea levels were about 25 metres higher. Continents were wandering very slowly. In the late Pliocene South America collided with North America, bringing about an interchange of flora and fauna and also bringing about a change in ocean currents and climate.
A collection of cold adapted mammals emerged from a variety of families. Where did they come from? Ice is the unifier of the Arctic, in its absence sea levels are higher and land mammals don’t enjoy the ability to wander from one side to the other. That makes it a poor candidate . The Antarctic continent is cut off by the Southern Ocean making it an even worse candidate.
By contrast the Tibetan Plateau even though close to the equator is at sufficient altitude to rival the true poles for cold weather. It was called the third pole by Marcel Kurz, the great Swiss geographer, mountaineer and explorer. It is well-connected to surrounding land masses meaning that a good variety of mammalian families were represented there during the good times of the Pliocene. As the cold times came on the Tibetan fauna adapted. During the height of the glaciations they could radiate out far to the north.
The Out of Tibet Hypothesis suggests that the Mammoth, Woolly Rhinoceros, the Three-toed Horse, Sabre-toothed Cat and other cold adapted megafauna originated in the Himalayan mountains. For example the Arctic Musk Ox and the Himalayan Takin are fairly closely related being the only extant members of the tribe Ovibovini.
Since most of the cold adapted megafauna shuffled off this mortal coil in the last 10,000 years you might be wondering where this is going. There are Musk Ox on Svalbard but I wasn’t lucky enough to see or photograph them but I did catch up with another creature that provides a strong link with Tibet …
At under 5kg they don’t qualify as megafauna but according to et al. the Arctic Fox is descended from the Early Pliocene (3.60–5.08 Myr ago) high altitude fox, Vulpes qiuzhudingi which they have recently discovered, and which they consider support for the Out of Tibet Hypothesis. The following figure is shamelessly stolen from their article.
The Arctic Fox has a fairly short life, typically 3 or 4 years, 10 or so if they are lucky. When food is abundant they can have large litters (as many as 25 – the largest litter size among the Carnivora) although 5 or 6 is more usual. This is a very different life strategy than the Polar Bear.
As can be seen in the photo above there are two colour morphs. This is genetically determined. On Svalbard 85 – 98% of the population is the white form. This despite the fact that the gene for the blue form is dominant. There is clearly some selection pressure against the blue form. This was certainly true in the fur hunting days when pelts of the blue form were worth considerably more.
If you do a Google search for Arctic Fox you will be overwhelmed with links for a semi-permanent, vegan haircolouring. An odd choice of name for a vegan product – the Arctic Fox is a ferocious little predator. Lemmings are high on the menu where they occur (no Lemmings on Svalbard) and birds elsewhere. They take carrion, seal pups and some plant food . When you see a Polar Bear there is often a fox not far away hoping to steal a few mouthfuls. Some food is cached for winter consumption.
Arctic Foxes are susceptible to rabies and toxoplasmosis. They are the final host of the tape worm Echinococcus multilocularis, a parasite that can be fatal in humans.The Norwegian Polar Institute recommends wearing gloves if you intend to handle fox faeces.
bobmcgee 