Fossils shed light on animal movement

James Marshall
September 6, 2019

The fossil of a worm that lived 550 million-years-ago may be the earliest known evidence of an animal walking on the Earth's surface, according to a new study. Named Yilingia spiciformis - that translates to spiky Yiling bug, Yiling being the Chinese city near the discovery site - the animal was found in multiple layers of rock by Xiao and Zhe Chen, Chuanming Zhou, and Xunlai Yuan from the Chinese Academy of Sciences' Nanjing Institute of Geology and Palaeontology.

The origins of movement in animal species remains fairly murky, though there is evidence of "directional movement" as early as 560 million years ago.

It was a flat, segmented animal with lots of tiny "legs", not too unlike a modern millipede. What is unique about this find is that the conserved fossil of the animal that rendered the trail versus the impenetrable conjecture where the body has not been conserved. Indentations in 550-million-year-old rocks in China confirmed the prediction.

Newly unearthed worm tracks have provided the earliest evidence of animal mobility.

An global research team recently discovered a segmented bilaterian fossil about 550 million years old in China, which represents one of the oldest mobile and segmented animals.

They include something even rarer: a fossilized "death march" or "mortichnium" - the trail produced by a Y spiciformis just before it died.

"Mobility made it possible for animals to make an unmistakable footprint on Earth, both literally and metaphorically", Shuhai Xiao, a professor of geosciences at Virginia Tech, said in a news release.

"The evolution of segments may have led to a transformative innovation" in animal movement that paved the way for an explosion of life in the Cambrian period that followed, the paper argues.

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

'We show that animal motility evolved almost 550 million years ago, although in a rather modest way'.

Remarkably, the find also marks what may be the first sign of decision making among animals - the trails suggest an effort to move toward or away from something, perhaps under the direction of a sophisticated central nerve system, Xiao said.

The animal that made those trails, which are seen regularly in the fossil record from the period, was a mystery until the discovery of the mortichnium - which neatly displayed a deceased Y spiciformis at the end of the trail.

"We are the most impactful animal on Earth", said Xiao.

One specimen is directly connected with the trace it produced immediately before death, thus allowing the authors to interpret other similar trace fossils that are preserved in the same unit but are not directly connected with the animals that produced them.

Other reports by Click Lancashire

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