BLACKSBURG, Va., Dec. 10 (UPI) -- Paleontologists from Virginia Tech have unearthed 530-million-year-old fossilized kinorhynch worms in South China. The discovery was detailed this week in the journal Scientific Reports.
The specimens are considerably older than other kinorhynch worms -- sometimes called mud dragons -- helping scientists fill a gap in the evolutionary timeline of kinorhynchs, a group of tiny invertebrates related to arthropods. They boast exoskeletons and segmented bodies, but lack jointed legs.
Scientists first began discovering kinorhynchs in 2013, but until now, researchers hadn't uncovered kinorhynchs as old as the oldest arthropods.
Study authors dubbed the latest kinorhynch species Eokinorhynchus rarus.
"Kinos represent an animal group that is related to arthropods -- insects, shrimps, spiders, etc. -- which are the most diverse group of animals on the planet," study author Shuhai Xiao, a professor of geobiology at Virginia Tech, said in a press release.
"Although arthropod fossils date back to more than 530 million years ago, no kino fossils have ever been reported," Xiao added. "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 worm fossil is just 0.078 inches long and 0.02 inches wide, roughly half the size of a rice grain.
By comparing the new specimens with their arthropod peers, scientists hope to be able to better understand the evolution of segmentation.
Teasing out the close evolutionary relationship between modern and ancient kinorhynchs will also help. The spinal structure and segmentation of Eokinorhynchus rarus suggest it is related to modern kinorhynch worms, of which there are 240 living species.
Now, scientists are digging for more specimens.
"Future discovery of additional kino fossil will offer important insights into the early evolutionary history of this group of tiny and little-known animals," said Xiao.