The Tibetan sand fox gets a lot of guff for its weird, square face. The slitted eyes don’t help this animal’s case. The critter just looks WEIRD. Now, for the first time ever, the animal’s extraordinary form is explained. By, ahem, me.

I saw footage of the fox last night on Planet Earth. Even as David Attenborough was marveling at the fox’s mystifying face, I detected the origins of that shape in the background of the shot. It was a reminder that all creatures — most creatures? many? — are shaped by geology, by the rise and fall of rocks.

So, some clues:

The geology of the Himalayas is young. Those mountains are fresh, and high, and hence subject to large-scale demolition as ice breaks off big, sharp chunks. (The soft hills of California’s coast, by contrast, are old: They change one sand grain at a time.)

The fox’s face is not shaped by bone, but by fur. Therefor the shape is all about appearance. (If the face were shaped by bone, it would be more likely that the animal had unusual skull/jaw muscles, tuned to unusual work.)

The shape of your typical fox face, seen head-on, is an upside-down pyramid: Narrow underneath; swelling at the top to accommodate brain and eyes; topped by wide-set ears. The shape of the Tibetan sand fox, seen head on, is not an upside-down pyramid.

The Tibetan sand fox is a stalking predator, sneaking up on ADORABLE, rabbity pikas. Its special challenge is to be invisible until the last moment. There aren’t any trees or shrubs to hide behind, on the Tibetan plateau.

Back to the rocks: Rocks are all there really is to work with on the Tibetan plateau. When a sharp, freshly busted rock tumbles off a Himalaya, it never comes to a rest in the position of an upside-down pyramid. Gravity isn’t into upside-down pyramids. Rocks are EXTREMELY obedient to the law of gravity.

So if you’re stalking among the rocks of the Tibetan plateau, with your face down in front of your paws, what shape would blend in best?

My theory, which is mine, ahem, is: The best shape is one that mimics a hunk of fallen rock, which is wide at the bottom. Compare the angles of the fox’s face to the angles in the rocks. She has even evolved a line of fur in front of the ear, to emphasize that pyramid shape.

OK, now the eyes: Why so narrow? Two reasons, I imagine. One, the lid forms an awning that reduces glare from the sun.

But the shape also helps the animal blend in. Circular objects are rare on the Himalayan plateau. All animals are automatic pattern-detectors. A pair of circular objects in a field of jagged objects is a noteworthy break in the pattern. Especially if they’re aimed at you, and especially if you’re a SUPERCUTE pika. A horizontal slit blends in a lot better.

There you go, David Attenborough. Weirdo fox deciphered.

For comparison, ye olde red fox, who has plenty of stuff to hide behind while stalking:

OK, since I have them on hand, I’ll add these: You can see that the skull of the Tibetan fox (left, viewed from top) and red fox (right, viewed from bottom) are essentially identical.

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