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Youti yuanshi, 520 million year old fossil unlocks insect evolution

NEWS - An exceptionally rare and detailed fossil, Youti yuanshi, provides a glimpse into one of the earliest ancestors of modern insects, spiders, crabs and centipedes. It was buried more than 520 million years ago in the Cambrian period, when the major groups of today’s animals first evolved.

Youti yuanshi, 520 million year old fossil unlocks insect evolution


The remarkable fossil of the euarthropod group that includes modern insects, spiders and crabs is a tiny larva no bigger than a poppy seed and has remarkably well-preserved internal organs.

Martin Smith of Durham University and colleagues from Yunnan University used advanced synchrotron X-ray tomography scanning techniques at the Diamond Light Source, a UK national synchrotron science facility. The researchers produced 3D images of a miniature brain region, digestive glands, a primitive circulatory system and even nerve traces for the larva’s rudimentary legs and eyes.

The fossil allowed the researchers to look beneath the skin of one of the earliest arthropod ancestors. The complexity of the anatomy suggests this early arthropod relative was far more advanced than previously thought – a developmental milestone crucial for understanding their evolution.

Larvae are so tiny and fragile that the chances of finding even one fossil are slim to none. This simple worm-like fossil is something special. The amazing structures preserved beneath its skin and intricate features have survived half a billion years of decay. 3D imaging of this remarkable tiny larva and the natural fossilization that achieved near-perfect preservation.

Studying this ancient larva provides key clues about the evolutionary steps required for a simple worm-like creature to evolve into a sophisticated arthropod body plan with specialized limbs, eyes and brains.

The complex head allowed arthropods to lead a wide variety of lifestyles and become the dominant organisms in the Cambrian seas. Details like these also help trace how modern arthropods acquired such incredible anatomical complexity and diversity and became the most abundant group of animals today.

The researchers suggest that this fossil fills a key gap in our understanding of how the arthropod body plan originated and became so successful during the Cambrian Explosion of life.

Original source:

Smith, M.R., Long, E.J., Dhungana, A. et al. Organ systems of a Cambrian euarthropod larva. Nature (2024). DOI:10.1038/s41586-024-07756-8

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