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305-Million-Year-Old Fossil a Window on Spider Evolution

The not-quite-a-spider fossil could shed light on the early evolutionary origins of modern-day spiders.

An international team of researchers has examined a 305-million-year-old, not-quite-a-spider fossil that could shed light on the early evolutionary origins of modern-day spiders.

The new, extinct species, dubbed Idmonarachne brasieri, was found in France in the 1980s, according to PhysOrg, but the fossil was partly encrusted in stone, so full examination wasn't possible until modern 3D scans gave scientists a closer look without risking damage to the specimen.

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"Our new fossil occupies a key position in the evolution of spiders," said the study's lead author Russell Garwood, of the University of Manchester, in a press release.

"It isn't a true spider," said Garwood, "but has given us new information regarding the order in which the bits of the anatomy we associate with spiders appeared as the group evolved."

The reason it's not a "true" spider, the researchers say, is because the ancient almost-spider lacked spinnerets, the special appendages modern spiders use to spin silk.

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"Our creature probably split off the spider line after [Attercopus], but before true spiders appeared," Garwood told the BBC.

"This fossil is the most closely related thing we have to a spider that isn't a spider," Garwood added – a creature about six-tenths of an inch long (1.5 millimeters), with legs and a jaw that were like those of spiders, just without the spinneret.

Garwood and his team's work was published today in the journal Proceedings of the Royal Society B.

This ancient fossil was almost a spider, but lacked a key piece of hardware: the appendage for spinning silk.

Insects and other creepy crawlies may be tiny, but their lineages are mighty, finds a new study that determined the common ancestor of mites and insects existed about 570 million years ago. The study, published in the latest issue of the journal Science, presents an evolutionary timeline that settles many longstanding uncertainties about insects and related species. It found that true insects first emerged about 479 million years ago, long before dinosaurs first walked the Earth. Co-author Karl Kjer, a Rutgers entomologist, explained that mites are arthropods, a group that's distantly related to insects. Spiders and crustaceans are also arthropods.

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Spiders such as the huntsman spider can, like mites, trace their lineages back to about 570 million years ago, according to the new study. The researchers believe that the common ancestor of mites, spiders and insects was a water-dweller.

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Millipedes, such as the one shown here, as well as centipedes are known as myriapods. The most recent common ancestor of myriapods and crustaceans lived about 550 million years ago. Again, this "mother of many bugs" would have been a marine dweller. Kjer explained, "You can't really expect anything to live on land without plants, and plants and insects colonized land at about the same time, around 480 million years ago. So any date before that is a sea creature." Moving forward in time, the most common ancestor of millipedes and centipedes existed a little over 400 million years ago. The leggy body plan has proven to be extremely successful.

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"This is an early insect that evolved before insects had wings," Kjer said. Its ancestry goes back about 420 million years. The common ancestor of silverfish living today first emerged about 250 million years ago. Dinosaurs and the earliest mammals likely would have then seen silverfish very similar to the ones that are alive now.

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Dragonflies and damselflies have family histories that go back about 406 million years. Kjer said that such insects looked differently then, however. "For example," he said, "they had visible antennae." Their distant ancestors were among the first animals on earth to fly.

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"Parasitic lice are interesting, because they probably needed either feathers or fur," Kjer said. As a result, they are the relative newbies to this list. Nonetheless, the researchers believe it is possible that ancestors of today's lice were around 120 million years ago, possibly living off of dinosaurs and other creatures then.

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Crickets, katydids and grasshoppers had a common ancestor that lived just over 200 million years ago, and a stem lineage that goes back even further to 248 million years ago. A trivia question might be: Which came first, these insects or grass? The insects predate the grass that they now often thrive in.

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Dinosaur Era fossils sometimes include what researchers call "roachoids," or wing impressions that were made by ancestors to today's roaches, mantids (like the praying mantis) and termites. "Some cockroaches are actually more closely related to termites than they are to other cockroaches," Kjer said, explaining that this makes tracing back their lineages somewhat confusing. He and his colleagues determined that the stem lineage goes back about 230 million years, while the earliest actual cockroach first emerged around 170 million years ago.

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Termites and cockroaches have a tightly interwoven family history. Termites similar to the ones we know today were around 138 million years ago. Now we often think of termites as pests, but they are good eats for many different animals, which back in the day would have included our primate ancestors.

Flies like houseflies that often buzz around homes belong to the order Diptera, which has a family tree that goes back 243 million years ago. The most recent common ancestor for modern flies lived about 158 million years ago, according to the study. There is little doubt that the earliest humans, and their primate predecessors, had to contend with pesky flies and all of the other insects mentioned on this list. All of these organisms are extremely hardy. The researchers determined that, in the history of our planet, there has only been one mass extinction event that had much impact on insects. It occurred 252 million years ago (the Permian mass extinction), and even it set the stage for the emergence of flies, cockroaches, termites and numerous other creepy crawlies.

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