|Cute duck couple: top left, male - bottom right, female.|
|Magic Eye of bunny-shaped circus peanuts. Cross your eyes and a new image will appear (j/k).|
|Imagine this, except black and rotten.|
Aside: both clams and mussels are bivalves, a class of animals which wriggled its way into existence around ~500 million years ago. This is twice as many years ago as when dinosaurs first appeared on earth. They have been around a loooooong time.The obvious next move was to chase the bird down and free it's foot, which we tried to do, but with no success. It soon occurred to us however, that if we were to catch the bird and remove the clam, what would we do with the clam?? It was then that we realized that the clam stood a much greater chance of survival if we left it alone, as the duck would likely return to some body of water sooner or later and the clam could then let go and fall to the bottom with the rest of its clam and fish friends...
...and someday maybe even retire as Ariel's bra.
For real though, what a triumph for the clam, attaching itself to that duck's foot! Think about it, that tiny little thing that usually has to move around by sticking a big foot/tongue thing out of its shell or clapping its shell together in a weird back-stroke move...
...it had managed to attach itself to an animal that had learned how to fly, and in so doing was attempting to spread his/her offspring further than it ever could have hoped to do otherwise. The clam had done it!!! His ancestors would be so proud!
We later discovered that Darwin had noticed this very phenomenon in 1882 (1):
"There can, I think, be no doubt that living bivalve shells must often be carried from pond to pond, and by the aid of birds occasionally even to great distances."FINALE: As noted above, bivalves came onto the scene ~500 million years ago, but the first birds didn't arrive until ~150 million years ago. In the ~350 million intervening years, bivalves honed their shell-clamping-shut abilities to adapt to life in the sea. However, when birds and their easily-clamp-able feet came along, they put this shell-clamping adaptation to use as a mechanism to spread their offspring to far off places via the sky! Clams learned how to fly too!
This re-purposing of an adaptation is known as an exaptation. Another example of an exaptation is the use of feathered-wings for flight, as the feathers were likely first evolved for heat-regulation and only later used in flight.
Life is so insane.
(1) Darwin, C. (1882) On the dispersal of freshwater bivalves. Nature 25:529-530.