Feeding Limbs Discovered in Ancient Sea Creature

Scientists have uncovered the preserved fossils of an ancient arthropod with primitive limbs under its head, according to a new study.

The fossilized animal, called fuxianhuiid, was unearthed in a new fossil-rich site in South China. Fuxianhuiid is a sea creature that existed around 520 million years ago, nearly 50 million years before primordial land animals first emerged from the sea onto land during the early part of the Cambrian explosion, when multi-cellular organisms rapidly evolved into diverse marine animals.

Until now, fossils found of fuxianhuiids had their heads obscured by a wide shell or "carapace", making it difficult for the researchers to make a detailed study of their internal organs. But, when a team of researchers from University of Cambridge in the U.K. and Yunnan University in Kunming, South China, excavated a fossil rich-site called Xiaoshiba in China, they found several specimens of fuxianhuiids with their bodies flipped over before fossilization.

One of the specimens was well-preserved. This allowed scientists to make a detailed examination of its head. They found that the fuxianhuiid had primitive limbs under its head, which were used to push food into the mouth as the arthropod crawled across the seabed millions of years ago. The discovery reveals one of the earliest evolutionary examples of limbs used for feeding, as well as the oldest nervous system that extended beyond the head in fossil records.

"Since biologists rely heavily on organization of head appendages to classify arthropod groups, such as insects and spiders, our study provides a crucial reference point for reconstructing the evolutionary history and relationships of the most diverse and abundant animals on Earth," Javier Ortega-Hernández, from Cambridge's Department of Earth Sciences, said in a statement. "This is as early as we can currently see into arthropod limb development."

Arthropods were the first jointed animals, enabling them to crawl. Fuxianhuiid-like sea creatures are likely to have evolved from creatures resembling worms with legs. They spent most of their time crawling across the seabed and using their limbs to shovel food into their mouths. They might also have used their bodies to swim for short distances, said the researchers.

They hope the findings would shed light on the evolution of the most primitive state of animals. "These fossils are our best window to see the most primitive state of animals as we know them - including us," said Ortega-Hernández. "Before that there is no clear indication in the fossil record of whether something was an animal or a plant - but we are still filling in the details, of which this is an important one."

The findings of the study are published in the journal Nature.