Washington: Researchers have unravelled an ancient missing link between today's spiders and their long-extinct ancestors, and that may help explain how spiders came to weave webs.

The research by scientists at the University of Kansas (KU) and Virginia's Hampden-Sydney College focuses on fossil animals called Attercopus fimbriunguis. While modern spiders make silk threads with modified appendages called spinnerets, the fossil animals wove broad sheets of silk from spigots on plates attached to the underside of their bodies. Unlike spiders, they had long tails.

The research was led by Paul Selden, professor of invertebrate paleontology in the department of geology at KU, and William Shear, professor of biology at Hampden-Sydney College.

Selden and Shear discovered the fossils almost 20 years ago. At that time the specimens were thought to be the oldest spider fossils known, dating back to the Devonian Period, about 380 million years ago.

Unearthed in upstate New York, the fossils were among the first animals to live on land in North America.

New finds near the same location, in Gilboa, New York, caused the paleontologists to reinterpret their original findings. The new fossils included silk-spinning organs, called spigots, arranged on the edges of broad plates making up the undersides of the animals.

The researchers identified parts of a long, jointed tail not found in any previously known spider, but common among some of the spiders' more primitive relatives, said a KU release.

"We think these 'tailed spiders' represent an entirely new kind of animal, not known before from living or fossil examples," Shear said. "They were more primitive than spiders in many ways, and may be spider ancestors." Besides having tails and spinning silk from broad plates, the animals also seem to lack poison glands. IANS