530-Million-Year-Old 'Mud Dragon' Worm Fossils Discovered In China

Researchers have discovered the fossilized remains of ancient microscopic worms, which date back to over 530 million years ago. The kinorhynch worm fossils, also known as 'mud dragons,' were found in Southern China. In their study, researchers' examined the relationship between kinorhynchs and arthropods, along with other small invertebrates that possess segmented bodies and exoskeletons.

The ancient mud dragons, or 'Eokinorhynchus rarus,' fossils existed during the Cambrian period (about 541-485 million years ago) and their bodies consisted of five pairs of large bilateral spines on their trunks. They were most likely related to modern kinorhynchs, according to the researchers.

"Although arthropod fossils date back to more than 530 million years ago, no kino fossils have ever been reported," Professor Shuhai Xiao, coauthor of the study and geobiology scientist at Virginia Tech, said in a news release. "This is a huge gap in the fossil record, with more than 540 million years of evolutionary history undocumented. Our discovery is the first report of kino fossils."

The new fossils are enabling the researchers to have a better understanding of the body segmentation and evolution of arthropods and small invertebrate animals. Also, the fossils shared several similarities to modern kinorhynchs, which revealed an ancestral/evolutionary pattern among the species. There is an average of 240 species of known living kinorhynch, all of which thrive in marine environments.

The fossilized specimen was 0.078 inches in length and 0.02 inches in width, which is about half the size of a grain of rice, according to the researchers.

"We used electron microscopy to thoroughly image the fossils' surface features, and then the microCT to scan their interior structures, including their midguts," said Drew Muscente, a coauthor of the study. "Because this suite of data is so comprehensive, it includes pretty much everything you can know about the morphologies of the fossils."

The fossil findings will enable the researchers to new information on the early evolution of kinorhynchs and other small invertebrates.

The findings of this study were published in Scientific Reports.

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