Fossils shed light on early animal movement

It’s got the moves: An artist’s reconstruction of the movement of Yilingia spiciformis worm. — AFP

Tokyo: More than half a billion years ago, a worm-like creature wriggled its last, creating a groove preserved as a fossil that offers new insights into some of the earliest animal movement.

The origins of movement in animal species remains fairly murky, though there is evidence of “directional movement” – as opposed to the meandering drift of a jellyfish for example – as early as 560 million years ago.

But records of such early movement are very rare, which makes a series of fossils that provide evidence of the life, and death, of the worm-like Yilingia spiciformis a key find.

Collected between 2013-2018 in southern China, the fossils show a segmented creature something like a millipede that lived 550 million years ago, long before dinosaurs roamed the Earth.

And they include something even rarer: a fossilised “death march” or “mortichnium” – the trail produced by a Yilingia just before it died.

The fossils provide the first “direct supporting evidence” of early movement by a segmented animal, Shuhai Xiao, a professor at Virginia Tech university’s geosciences department, said.

Experts had long theorised that segmented animals were capable of movement in this time period, but there was no fossil evidence to support the idea.

Experts generally believe animals began to move around during a period known as the Ediacaran era, about 635 million to 540 million years ago.

But those animals left individual footprints or tooth marks from scraping as they passed over a surface.

“Yilingia is different because it produced long and continuous trails,” Xiao said.

The animal that made those long and continuous trails, which are seen regularly in the fossil record from the period, was a mystery until the discovery of the mortichnium.

The conclusions Xiao and his colleagues draw, published Thursday in the journal Nature, are thanks to the mortichnium, a vanishingly rare find in the world of fossils.

“Think about how many footprints a person would make in its lifetime,” Xiao said.

“What is the chance of this person being fossilised together with one of its footprints? Very slim.” — AFP

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