It’s swelteringly hot and humid on this tropical floodplain south of the equator. Ripples generated in the soft mud before the water receded are starting to bake in when, as the sun sets, the land feels something new – a pressure different from that of wind or water. Different from the clasp of algae and liverworts, or more the aggressive penetration of roots. Different even from the pulse of burrowing worms or molluscs or the tickle of arthropod feet.
The land feels the press of a flesh-and-bone body, weighing heavy out of water so that each step leaves a deep impression, those of the forelimbs smaller than the hind ones. There’s a need to rest often, belly to mud, gulping moist air into rudimentary lungs. The risk of overheating and desiccation is high. On the plus side, there are all kinds of squirming, scuttling prey to snap up, and none of the larger predators with which the nearby water throngs.
Another flood is coming; drifts of silt fill the tracks. Sediment lithifies, continents slip, rock accumulates, ruckles, fractures and weathers again. Earth whips around the sun, vacillates in and out of ice ages. Epochs pass – 380m years like a long dream.
New creatures come. They stand on the same mud surface, which has been preserved by chances as slim as the geology is ancient, and exposed by the wave action of a new-old ocean at the edge of a landmass now on the farthest rocky edge of western Europe.
At their feet, two rows of regularly shaped, evenly spaced depressions, traversing 15 metres of rippled stone. And here, a scuff where a belly slid, and there, a couple of sweeping curves where a tail dragged behind a swinging body in a motion that was still distinctly fishlike.
Of the three known preserved trackways of such antiquity worldwide, none are anything like as long as this, with more than 145 individual footprints marking the second earliest known movement of four-legged vertebrate life on land.
The creatures look at the feet on their own hindlimbs and the hands that gesticulated at the ends of their forelimbs. They watch as the wind and the waves continue their work. And they wonder if, in some way, we have all been here before. And the Earth keeps spinning, the sun burns on.
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