US fossil spins web of intrigue

[Lionel]

The ancient cousins of modern spiders could have been spinning webs 55 million years before the reign of the dinosaurs, a scientist says.

What appear to be silk-spinning structures have been found on the body of an ancient arachnid fossil.

The 300-million-year-old creature, Aphantomartus pustulatus, could have used silk threads to trap prey.

It is a trigonotarbid, part of a group of ancient arthropods that were among the first animals to colonise land.

Trigonotarbids are not true spiders but are thought to be related. If they really could spin webs - which some scientists doubt - they may be more closely related to spiders than previously thought.

Early evolution

The fossil evidence also suggests that silk-spinning could have evolved independently in many arachnid lines and may one day be found in other extinct arthropods.

"We all know that spiders and some insects, such as moths, produce silk, but to my knowledge, silk-spinning has never been demonstrated in an extinct fossil group," says Cary Easterday, a master's degree student in geological sciences at Ohio State University. "This would be a first."

The fossil, which was found at a mine in Ohio, is unusually well preserved. Under the microscope, tiny bumps, known as microtubercles, can be seen running down parts of both rear legs and all over the body.

Easterday admits that the evidence for silk-spinning is not conclusive. They could be cleaning structures, he says, or specialised hairs that trigger fight-or-flight responses.

Paul Hillyard, Curator of Spiders at the National History Museum, London, says the structures resemble those found in a group of modern spiders known as cribellates.

The tree-dwellers have microtubercles containing a single hair on the back of their legs which they use to comb out fine threads of silk to make webs. But he is not convinced that the same thing happened in trigonotarbids.

"If these microtubercles were found only on the legs, I would be more convinced", he told BBC News Online, "but they are found on the body as well."

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