I’m sure that just about everyone has seen the footage of the Tibetan fox. Its blocky head is really unique among canids, and one theory about why it has such an unusual head is that the head actually makes the fox more camouflaged around rocks as it stalks its prey.
If you’ve not seen the footage, here it is:
The Tibetan fox is found in the Tibetan and Ladakh Plateaus, and it pretty much found only in high grasslands. It is a specialist of this environment.
The mitochondrial genome of this species was sequenced recently. Preliminary studies had indicated that its closest relative is the corsac fox, which ranges in the steppe country that runs from the eastern edge of the Caucasus to northeastern China. It lives in arid, semi-arid, and grassland habitats to the north of the core range of the Tibetan fox.
The corsac is the basic fox. It is smaller than most red foxes, and it comes in gray or reddish brown.
And to be completely honest with you, I have a very hard time telling corsac foxes from North American swift foxes (Vulpes velox). I should note that even though the two look alike, the corsac is more closely related to the red fox, while the swift fox* is very close to the arctic fox (Vulpes lagogpus). Both swift and corsac foxes are adapted to grassland ecosystems, so their similarities can be chalked up to simple convergent evolution.
The researchers who sequenced the Tibetan fox mitochondrial genome also looked at other dog species and found that modern dog species radiated very rapidly. The authors estimate less than 5 million years separates Canis species from the maned wolf, which is actually quite about half the time that has been estimated for the divergence between Canis and its allies and the South American wild dogs through the sequencing of the dog genome.
Mitochondrial DNA studies can lead us astray, but this is still an interesting find.
The researchers found that the corsac and Tibetan foxes split from each other about 1 million years ago. Although they don’t say so in the paper, it’s pretty likely that the corsac is the ancestor of the Tibetan fox. Maybe it happened like this:
A population of corsac foxes, whose range had been pushed south during the Pleistocene, were able to roam into the Tibetan Plateau during a warming period. They were then cut off by glaciers and began their journey toward speciation, adapting the high grassland habitat in ways that made them quite different from their ancestors. The squared off heads gave the foxes marginal advantages in hunting in the high, rocky grasslands.
The authors didn’t find any genetic evidence of any sort of adaptations in the mitochondrial genome for higher altitude living among Tibetan foxes. Those genes probably do exist, but they don’t exist in the mitochondrial genome.
So what the researchers found is that Tibetan fox is very closely related to the corsac fox. This is not a surprising find, but I have wondered where this fox really does fit in the dog family. It’s from such an isolated area that virtually no studies have been done on it.
The squareness of its head makes the Tibetan fox a bit of a celebrity in the digital age. If BBC cameras hadn’t filmed it (twice!), it wouldn’t really be known. I’d only ever heard of it from a children’s book, which included a bad painting of one. It was just a nondescript fox as far as I was concerned.
So the Tibetan fox is a modification on the basic fox.
It evolved from the banal to the bizarre.
Bizarre enough to be on the BBC.
*The study looked at kit foxes. Kit foxes are closely related to swift foxes. Both are very closely related to the arctic fox.