Excellent response, kethoticus! Even if I were to come across a keyboard on a beach, I would be very reluctant to view it as anything other than man-made.
Years ago Microsoft sold a keyboard which they called the "Natural Keyboard". It had a huge hump in the middle, making it very difficult to use. Nevertheless, it had its advocates. If you wish to use one of them, you may need to get a PS/2-to-USB adapter, such as those sold by CyberGuys.
Before that, there were some so-called "ergonomic" keyboards with a variety of gimmicks, such as hinges in the middle. Even Apple sold keyboards of that type. Apple's were all ADB; I've never used one. Again, if you find one, you can use an ADB-to-USB adapter.
I think the "ergonomic" fad has died out. The only residual is stickers you sometimes see on keyboards that say "Use of ANY keyboard will probably cripple you for life," or words to that effect. For people who take such warnings seriously, I recommend a pint of Bass Ale (or two) followed by a long afternoon nap.