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520-Million-Year-Old Fossil Larva Preserved in 3D

The larva has a segmented body, with two large structures on its head, four pairs of branching legs and three additional pairs of legs.

If you think finding a needle in a haystack sounds challenging, try searching for fossils the size of fingernail clippings in massive slabs of rock.

But that's just what a team of scientists is doing at a site in Chengjiang, China. And they recently struck a fossil jackpot, discovering an extremely rare arthropod larva fossil measuring a mere 0.08 inches (2 millimeters) long.

The fossil, estimated to be 520 million years old, was preserved in 3D, presenting the researchers with an exceptional level of detail for this very early stage of the creature's development. It also provided them with a first glimpse of ancestral larval forms in arthropods, the invertebrate animal group with exoskeletons and segmented bodies that includes arachnids, crustaceans and insects. [Photos: A Cambrian Larva With a 'Daggerlike' Tail]

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The larva has a segmented body, with two large structures on its head, four pairs of branching legs and three additional pairs of legs that are much less developed. Its posterior is tipped with a "dagger-like" appendage, framed by two triangular forms resembling paddles, which the scientists suggest may have been used for swimming.

This is the first fossil of its kind to be found at Chengjiang since the site's discovery in 1984, according to Yu Liu, the study's lead author and a postdoctoral researcher at the Ludwig-Maximilians-Universität in Munich.

The researchers identified the tiny fossil as a known species - Leanchoilia illecebrosa, a member of the "short great appendage arthropods," which earned their name due to the large claw-like structures attached to their heads, likely used for feeding or for sensing their environment.

In fact, it was the shape of those appendages in the larva fossil that helped the scientists with their identification, Liu told Live Science in an email.

But compared to adult forms, other limbs in the fossil were not as well developed. This told the scientists that the new discovery represented an early larval stage, Liu said.

Hidden in rock

Finding fossils this small is no easy task. It begins with removing large slabs of rock, splitting them into somewhat smaller slabs, and then reviewing them with a magnifying lens to see if there might be "something interesting" preserved in them, according to Liu.

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"As you may imagine, the chance of finding a fossil is not very high," Liu told Live Science. "In most cases, you get one fossil after separating tens of slabs. The chance of finding a GOOD fossil is even lower. You need to separate hundreds or even thousands of slabs for that."

Such tiny and delicate specimens like this one can't be isolated from the rocky material around them with the methods traditionally used for chipping out larger fossils. Paleontologists use microphotography and scanning technology rather than picks, drills, or chisels to "penetrate" the rock and show them the remains of once-living animals preserved inside.

3D surprise

And finding such a small fossil preserved in 3D was unexpected and exciting, Liu said. Micro computed tomography - micro-CT scans - of the larva offered a highly detailed picture of its body, with an interesting surprise as a result.

This particular larva's body type - one in which body segments are added as the creature grows to adulthood - was already thought to be typical for modern crustaceans, Liu said. But, finding one this far back in the fossil record hints that this was a feature in all other arthropod ancestors, as well.

This rare find represents an important puzzle piece for investigating the mysteries of the Cambrian radiation - an evolutionary boom period that began about 543 million years ago and lasted around 53 million years - the researchers wrote in their study. Understanding these ancient animals' stages of development could help to unravel the mechanisms that gave rise to the unprecedented diversity of living forms in Earth's distant past.

The findings were published online May 2 in the journal Proceedings of the National Academy of Sciences.

Original article on Live Science.

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Fabulous Fossils: Gallery of Earliest Animal Organs In Photos: Bizarre Parasites From the Past Image Gallery: Bizarre Cambrian Creature Copyright 2016 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

An adult form of the Cambrian arthropod, Leanchoilia illecebrosa.

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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