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How Crab Brain Fossils from 310 Million Years Ago Were Preserved

Researchers say a newly analyzed specimen is a "one million" discovery.

Monday, 23rd August 2021

Paleontologists can spend years carefully splitting rocks to find the perfect fossil. But nature made this work with horseshoe crab brains from 310 million years ago, breaking up the fossils in the right way to reveal the central nervous system of ancient arthropods.


In all soft tissues, it is well known that the brain is difficult to preserve in any form. Russell Bicknell, an evolutionary paleontologist at the University of New England in Armidale, Australia, said that these detailed specimens were discovered by pure chance."


Bicknell and his colleagues reported in Geology on July 26 that the fossilized brain is very similar to that of the modern horseshoe crabs, providing clues to the evolution of arthropods. And the unique way of preservation of the brain can lead paleontologists to find new places to find soft-tissue fossils that are hard to find.


The fossil record of horseshoe crabs spans approximately 445 million years. But having an extensive fossil record is one thing. For many animals, including crabs, their soft tissue fossils are extremely rare, because the tissue degradation rate is often much faster than the rate of fossilization. It is especially rare to find the delicate fat structures that form the brain in rocks. So far, only about 20 fossil arthropod nerve tissue samples have been identified.


The newly described brain is part of a larger fossil of the extinct Euproops Danae discovered by Bicknell at the Yale Peabody Museum of Natural History, originally unearthed from the Masson Creek fossil bed about an hour southwest of Chicago. Victoria McCoy, a paleontologist at the University of Wisconsin-Milwaukee, said the site is one of the only places in the world known to save the structure of the brain.


"The fossils at Mazon Creek are really special," McCoy explained. "This is interesting because the fossils are kept in nodules." Nodules are spherical rocks formed around a central block of material, like a crab that has been dead for a long time. Most of the nodules in other fossil layers have no fossils or the fossils are just bones and hard parts, but "Mazon Creek has very good soft tissue in these nodules," he said.


In Chapter, the scientists say that this low-oxygen environment almost certainly slows down the breakdown of tissues, allowing time to preserve it. In an environment that contains oxygen, the recession can occur in a few weeks and the brain can die too quickly.


The actual preservation process is a multi-step test, Bicknell said. "First of all, of course, the horseshoe crab must die." As the crab rots and is surrounded by mud without much oxygen, the siderite covers the crab's body and preserves its fragile brain structure. After the brain degenerates, the siderite "mold" is filled with a pale clay mineral called kaolinite, forming a white brain structure that stands out from the original tan fossils. Over time, a rock sphere formed around the fossil, which eventually ruptured accidentally.


According to research on similar modern environments (such as the North Norfolk Moors in England), the entire conservation process may have taken less than 50 years, McCoy said. This is much faster than other fossilization processes, which may take thousands of years or more. "Nerve tissue breaks down very quickly. We have no reason to think it will be stable," he said. "Although we do not fully understand how nodules are formed, all the evidence so far shows that it is the nodules themselves that prevent things from breaking down."


The high-quality preservation of these siderite nodules may indicate to paleontologists Looking for new directions for soft-tissue fossils. So far, only a few environments capable of producing siderite nodules have been identified in the rock record, but these locations may be actual targets for future fossil searches.


"The most important part here is that, purely by accident, the fossil splits throughout the brain," Bicknell said. The tuberculosis is broken in the right direction to reveal a nearly perfect cross-section of the brain structure. "If it was not destroyed in this way, we would not have this level of information. In the end, he was very lucky."


The researcher said that the preserved central nervous system can give us insight into the behavior of ancient crabs. Because the fossil brain is very similar to the brain of modern horseshoe crabs, Bicknell said that it is safe to say that the walking, breathing, and even eating habits of ancient animals may be similar to those of horseshoe crabs today, even eating with their legs... "Imagine eating with elbows. Hamburger," Bickernell said.


The News Talkie Bureau



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