Our Earliest Example of an Animal Moving on Its Own

Here’s the footprint of an Earthling a long, long way from home.

By Robert Krulwich
photographs by NASA
Published 7 Nov 2017, 14:04 GMT
Courtesy NASA

You know the one—it’s Neil Armstrong’s boot print on the surface of the moon. “A giant leap,” he called it. Well, here’s another leap—arguably just as “giant,” though a touch more obscure. It was discovered in a dark slab of rock that hangs on the edge of the North Atlantic in a remote corner of Newfoundland.

Photograph by Dr Alex Liu, University of Bristol

It’s an impression left by another Earthling, an odd-looking ocean dweller that lived roughly 565 million years ago and that was maybe the first creature—certainly the first we know of—to use its own muscles to move from where it was to someplace new.

We call them Ediacarans, or more properly, ‘ediacaran organisms’. They’re a weird family, some flowerlike, some like little plops of mud, this one a little like a palm leaf or maybe a ribbed pancake.

Photograph by O. Louis Mazzatenta, National Geographic Creative

But what a pancake! As described by Robert Moor in his new book, On Trails: An Exploration, one of these things.

““… did something virtually unprecedented on this planet—it shivered, swelled, reached forth, scrunched up, and in doing so, at an imperceptibly slow pace, began to move across the sea floor, leaving a trail behind it.””

The path it carved that day in the ocean mud—now frozen and fossilised—is the oldest trail we’ve ever seen on Earth, laughably small compared to Neil Armstrong’s journey, but it’s The Beginning, our beginning, the very first evidence of animal-like locomotion.

A volcano must have poured lava on a patch of ocean millions of years ago, freezing every living creature in place, until slowly the earth shifted, and the rock layer surfaced, then got sculpted and exposed, so now if you go to Mistaken Point on the Newfoundland coast, you can see scores of them, fern-like, blob-like, pancake-like.

Photograph by Dr Alex Liu, University of Bristol

This is a famous site, well-known to fossil hunters. But, as sometimes happens, new eyes can find what everybody else missed, and when a young paleobiologist from Oxford, Alexander Liu, came by in 2008 and scrunched down to see what he could (this is him lying sideways on the rocks, shoes off, booties on to protect the fossils).

Photograph by Jack Matthews

… he noticed what first looked like a slime trail, a thumb-wide path that crossed the rock surface.

Photograph by Dr Alex Liu, University of Bristol

Moor visited more recently, and when he ran his fingers over this same fossil pathway (there were a bunch of them on those rocks) he wrote, “They bore the distinct texture of life. Their surface was patterned with a series of nesting arcs.” You can see these clearly at the upper end, but they’re in the middle too.

Photograph by Dr Alex Liu, University of Bristol

Those may be the traces of a suction cup foot that these creatures probably used to fasten themselves to rocks or flat surfaces on the ocean bottom. Sea anemones behave that way today: they latch on to flat ground but occasionally pry themselves loose and take lumbering 'steps' when it’s time to travel.

In 2009, Alexander Liu and colleagues wrote a paper suggesting that these ancient creatures were not floating or squirming or rolling or reaching. No, they were 'crawling'. These were primitive proto-steps, and you can see each step as a series of nesting parentheses.

Critics said they could just as easily be tracks made by pebbles tossed by waves, but when the experts looked, most concluded Liu is right. Those aren’t pebble tracks. Those are trails—our earliest evidence of locomotion, of life on the move.

Why Go Anywhere?

The question is, Why bother? Why move?

Were they hunting food? Looking for sex? Fleeing a predator? Or—and here I get back to Neil Armstrong—were they just on a walkabout, wondering what lies beyond the next hump of sand?

There wasn’t a lot going on in the ocean 565 million years ago. The Earth was recovering from a deep chill that left the sea bottoms, Moor writes, “devoid of predators,” empty-ish. Same for the sea. There wasn’t much to look at: “Perhaps a primitive jellyfish would have passed overhead like a living cloud.”

Photograph by Robert Krulwich

With no pressing reason to move about, I’m thinking that maybe what pushed these pioneers to travel was (how to put this?) a touch of restlessness, a behaviour that would be passed down the great chain of life as animals moved in greater arcs, butterflying their way to Mexico, flying from Canada to the tip of Argentina, circumnavigating the globe, lifting off the planet, and, ultimately, landing on the moon.

That’s why we move, I like to think: to see, to stretch, to have more choices.

But when Moor asks this same question (“Why do we, as animals, uproot ourselves and go somewhere else?”) he doesn’t go to restlessness. The creatures that invented locomotion, paleobiologist Liu tells him, probably wanted security—a clean, flat surface to cling to. Surfaces crack, shift. When life becomes too hard where you are, you go to where it’s easier.

They didn’t want adventure, they wanted comfort.

The two explanations sound opposite, but they’re not. No place stays safe forever, not even our little blue planet. At some point, out of restlessness or desperation, it doesn’t matter which, you have to do that thing that the pancakes invented 565 million years ago—you don’t have a choice. Nature knew that early. So Earthlings learned it early.

You either move—or you die.

So we moved. And we never stopped.

Robert Moor’s  book On Trails: An Exploration is a meditation on paths—not just the paths that ancient creatures made, but also ant paths, elephant paths, footpaths, the paths in our brains and in our machines. Moor, a guy who likes to walk, does the full Appalachian Trail from Georgia to Maine, walks along highways, loses a trail full of sheep, messes with ants, befriends all sorts of fellow walkers, and as he wanders, he wonders how paths form, change and last. Hanging with him you meet a host of different byways, get in (and out) of trouble and the experience is not just enlightening, it’s sweaty, hot, cold and … well, to say it plainly … fun.

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