Over the past few days I've been reading a book about the famous Iguanodon site at Bernissart, Belgium. (Well, okay, maybe the site is only famous among vertebrate paleontologists.)
Iguanodon is a dinosaur perhaps best known for the spikes on its thumbs. It is unknown if the spikes were used for defense against predators, in intra-specific combat, or in feeding. I've been thinking, though, that the thumb spikes would have been perfect for hitch-hiking.
This theory could have been the basis for a Far Side cartoon, showing an Iguanodon standing next to a highway thumbing a ride, with the caption "The real reason Iguanodon had thumb spikes", along the same lines as the famous "The real reason dinosaurs became extinct" cartoon.
Or, alternately, the cartoon could show a car pulling up to an Iguanodon on the side of the road, who angrily declares, "I'm not hitch-hiking, I'm an Iguanodon!", with the same sense of saurian outrage displayed in the "Well, of course I did it in cold blood,you idiot! ... I'm a reptile!" cartoon.
(I was surprised to learn in researching this post that there is apparently no official online archive of Far Side cartoons.)
On a side note, from what I understand, hitch-hiking is still popular in Europe, but it has been virtually extinct in the United States for decades. In the course of my entire life I can recall seeing only one or two hitch-hikers. There is an odd sort of "mutual assured destruction" doctrine in people's minds—if you go hitch-hiking, the person who picks you up will murder you, and if you pick up a hitch-hiker, the hitch-hiker will murder you.
Perhaps we would be less apprehensive about hitch-hiking if we had thumb spikes to defend ourselves.