As a science fiction writer, one of my hobbies is comparative anatomy. It is important for me to know how various organisms on Earth have solved the problems of moving, eating, seeing, and so on in order to build plausible aliens (or modifications for human beings). Evolution is constantly throwing things at the wall to see what sticks, and that churn produces some really interesting solutions to mundane-seeming problems.
Take walking, for example. Most of our familiar walking creatures (except bugs) are based on the tetrapod body plan. Four limbs, two on a pelvis and two up near a head. As evolutionary pressures drive a species to be bigger and bigger, their limbs become more robust to support the extra weight. Evolution is not an intelligent process, and so every solution is quick and dirty, thrown together from preexisting parts and driven as much by chance as by natural selection. Thus, animals with superficially similar body plans may, on closer examination, have wildly different anatomies.
Everyone’s favorite cuddly megafauna, the elephant, walks on its toes. Its weight is carried on an enormous shock absorber made of fat and connective tissue that sits behind its toes. This system works so well for the elephant that they can move almost silently. From a human point of view, elephant feet look right. They bend in the right places, and the idea of walking along on one’s splayed fingertips isn’t too alien.
It’s easy to assume that elephantine dinosaurs had feet like elephants, especially when they are so often illustrated that way. The first clue that this isn’t the case is in the tracks: some sauropods leave crescent-shaped tracks. Next, there’s the skeleton. Except for the thumb, the toes of Eusauropoda are blunt, clawless nubs. These multi-ton dinosaurs walked on the ends of their metacarpal bones — the bones which, in humans, form the back of the hand.
How strange this must have looked! As a writer, imagining the motion of such an animal and then translating that movement onto the page is a glorious challenge. I can look at reconstructions, or I can press my hands into odd shapes and imagine what it would be like to walk on a column of hand-bones. Where the animal’s wrist would be, and how it would bend… All the things I must keep in mind if I write such a creature into a story.
For more detailed information and pictures, see the Tetrapod Zoologist. I highly recommend that blog as a resource for cool animal facts and analysis.
For further examples of strange creatures that have lived on our planet at one time or another, see Mark Witton’s Flickr gallery.