Darwin expressly denied that natural selection necessarily produces creatures that are notably superior to their predecessors. He had spent a long time studying barnacles, after all, and barnacles are astonishingly successful--we find them everywhere. But they descended from free-living, shrimplike ancestors and became barnacles by losing their brains and sticking themselves head-first to rocks--hardly a great leap forward, but it worked.

Diatryma was flightless, like a modern emu--it was much too big to fly--but it was far more formidable. It stood over six feet tall and, unlike an emu, was seriously sturdy. Most impressive, however, was its enormous head--about the size of a modern pony's--with a commensurately huge hooked beak like a giant eagle's. Diatryma seems to have been related to modern fowl such as chickens, which might not seem too impressive until we consider the sheer belligerence of chickens in the form of fighting cocks.

It is possible too that Diatryma used its huge beak as a scythe for slicing coarse vegetation. But the most obvious guess is that it was a predator, reminding us that birds are descended from dinosaurs. Here, perhaps, was a Tertiary reincarnation of Tyrannosaurus rex--somewhat miniaturized but formidable nonetheless. Perhaps the nearest equivalent in the modern world is the cassowary, which can disembowel the unwary wanderer with one stroke of its prodigious clawed feet.