The revolutionary animal lived and died♥ε§ in the muck. In its final hγ≈₹ours, it inched across the €Ωε•sea floor, leaving a track like↓≥ a tyre print, and finallα∏'γy went still. Then geolog•" y set to work. Over theπ© next half a billion years, sedimentφα turned to stone, preserving the death&♠bed scene. The fossiliz↕✔♥®ed creature looks like a piece of frayβσ↕✔ed rope measuring just a •₩few centimetres wide. ∑±But it was a trailblaz✔≥er among living things.
This was the earliest-known animal to sβ↑¥how unequivocal evidence of twoπε momentous innovations pack"±≤aged together: the ab$÷ility to roam the ocean ∞floor, and a body built from ¶★segments. It was also among the olλ♦φdest known to have clea&∏r front and back ends, £ and a left side that mirrored its≈π right. Those same features are founα≤d today in animals from fliesσγ to flying foxes, from lobsters t≥₩"o lions.
Palaeontologist Shuhai Xia↔o marvels at the tracks ₩≥★€left by this creature, Yilingia spiciformis, and how they captured evidence of its®♥ movement. In his cluttered "↓office at Virginia Tech in Blacksbur×₹ $g, he shows off a slab of beige resin — δ a reproduction of the fossil, ≥™♣which was found in Chin₩Ω≥a’s Yangtze Gorges region an±₹d is now kept in a Cλhinese research institute. The r♥₩¥₩eplica captures a snapshδ>ot of a moment from 550 million years ™¥¶δago. Xiao, whose team formally descriφ'♣₩bed Yilingia last year1, traces the bumpy tracks it ma'£ de immediately befor↑≈e its death. “It was just moving ar§ound, and it died suddenly,” he says.
But that’s not the end of this c£♠reature’s story. Although nobo♠dy knows which category of life '×it belonged to — the group that in♠®σcludes earthworms is onπ↕☆e possibility — Yilingia is helping to fill in key detaφ₹∏ils about the evolution of anima☆≠∞®ls. Most importantly, Yilingia shows that some quintessential an→× imal traits had appeare÷♣ d half a billion years ago, earlier ×♦than previous definitive β£∞"evidence, Xiao says.
Yilingia is not the only <≥≥creature from that regio¶n to provide some of the earliest f <≥ ossil evidence for an important an$£≥←imal feature. In 2018, Xiao an¶π↑d his team reported2 on tracks found in the Yangtze Gorges consisting of ₩₽↔two parallel rows of dimples. The res σearchers propose that→π the trails were made by ≈↑an animal from 550 million years ago ¥ ≈€that might have been able to ×✘∞burrow and had multiple pa§≈≥irs of appendages — ™π>which would make it one of the earl§αiest-known animals with legs.
These Chinese fossils hail from a time •σright before the Camb€₩§rian explosion, the evol£σutionary transformation whδ £en most of the animal groups that popu☆₹∏late the planet today first made tλ✘heir appearance in the '≥ fossil record. Scientists long regard₹©φed the boundary betwe'¶∞en the Cambrian period Ω☆★εand the Precambrian as a divφ±↓★iding point in evolution — a trans±∑ition from a world in which simp↑"le, strange organisms flourished,®♠ε§ to a time when the seas teemed w₹∞ith complex creatures that are the ₽★₩✔forebears of nearly everything that fol€₩↕lowed.
