Around 520 million years ago, a tiny larva was stuck in mud in what is now China’s Yunnan Province. Fast forward millions of years, and this larva’s perfectly preserved fossil has given researchers at Durham University a closer look at the evolution of arthropods.
The fossil, known as Youti yuanshi, is so well-preserved that its exoskeleton and even the outlines of its internal organs are visible under a microscope. This ancient creature existed during the Cambrian Explosion, a period when many animal groups first appeared in the fossil record.
Upon closer examination, researchers found that Y. yuanshi shares features with both ancient and modern arthropods. It belonged to a group of extinct arthropods called lobopodians, characterized by long bodies and stubby legs. The larva had a pair of lobopods in each of its twenty segments, with segments getting shorter towards the rear. It also had a mouth but no anus, meaning it likely ingested food and expelled waste through the same opening.
Inside Y. yuanshi’s body, researchers found clues about its internal anatomy. The larva had a perivisceral cavity surrounding a tube believed to be its gut. Each segment contained voids thought to be digestive glands. In its head, a circumoral nerve ring connected to nerves that extended to eyes and appendages. The empty chamber in the head gave researchers a glimpse into the structure of the larva’s brain.
Y. yuanshi displayed features common to both extinct and extant arthropods, shedding light on the evolution of these creatures. For example, its protocerebrum, a precursor to the first segment of the arthropod brain, is a feature found in all arthropods today. The larva’s circulatory system resembled that of modern arthropods, particularly crustaceans.
While Y. yuanshi’s larval form reveals much about early arthropod development, mysteries remain. Researchers speculate about its adult form, wondering if it developed compound eyes or swimming flaps. The larva’s connection to known species of lobopods is also uncertain, leaving room for further exploration.
This microscopic fossil has provided invaluable insights into the origins of arthropods, offering a glimpse into a pivotal moment in Earth’s ancient history. As researchers continue to unravel the secrets of Youti yuanshi, we may gain a deeper understanding of the diverse and fascinating world of arthropods.
