Found: The World's Oldest Footprints, Made by Ancient Bugs

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Roughly 551 to 540 million years ago, a tiny critter wriggled around the ocean floor in what is now the area near the Yangtze Gorges in southern China. As it went about its day, the arthropod or annelid (or perhaps its ancestor) left behind two parallel rows of itty-bitty footprints in the sediment.

Millennia upon millennia later, a team of scientists uncovered a slab of limestone with markings that puzzled them. They tilted the rock in various directions towards the sun, and when the light hit the stone just right, they uncovered little trackways engraved in the limestone. On further analysis, they discovered the footprints were beyond pre-historic—they surpassed the oldest fossilized footprints ever found by 10 million years.

The longest trackway is 4.3 inches long, so the researchers estimate the animals that made it were around 0.47 inches in length. It's unclear how many legs it had, what type of arthropod or annelid it was, or how it died.

While there are few facts about the creature itself, the find is a surprising discovery for many reasons. During the Ediacaran period, which spanned 635 million years ago to 541 million years ago, "sediments were not strongly disturbed (animals were few; many animals were immobile; the mobile ones did not significantly churn the sediment)," wrote Virginia Tech University geobiologist Shuhai Xiao in an email.

So, even though the fossil record for tiny invertebrates of this sort is sparse, these prints were preserved nicely because there was minimal foot traffic.

The major clues from the research lie in the animal's appendages and movement. The scattering of these animals would shake the sediment in the ocean floor. "Doing so, they bring oxygen to the sediment and oxidize organic carbon and other chemicals that would otherwise be buried in the sediment," wrote Xiao. This may have greatly affected the way the Earth's climate and geochemical cycles function today.

"This is just one example of how legged creatures can change the world," wrote Xiao.