Two tiny craters, each smaller than an aspirin pill, contain fossilized nerve tissue dating back 508 million years. The Cambrian insect-like creatures could help scientists piece together the evolutionary history of modern-day spiders and scorpions.
However, it is not clear exactly where these fossils are – both types symmetrical soft wood That fits right into the arthropod evolution tree, said Nicholas Strausfeld, a trustee professor in the Department of Neuroscience at the University of Arizona, who was not involved in the study.
That’s because some features, such as animal eyes and nerve cords, can be clearly identified in fossils, but other parts of Nervous system It is not easily monitored. In particular, it’s unclear whether the animals carry a brain-like bundle of nerves called SYNGANGLION, and without this basic evidence, their relationship to other animals remains a mystery, Straussfeld said.
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Where you’ll be mating will sit, instead, there’s “this mess in the middle of the head,” said first author Javier Ortega Hernandez, an invertebrate paleobiologist at Harvard and curator of the Harvard Museum of Comparative Zoology. Researchers can tell that this mess is neural tissue, but they can’t discern its exact organization.
“It’s true … we don’t have every feature of the nervous system of this animal, because fossils tell us a lot,” said Ortega Hernandez. The researchers acknowledge this uncertainty in their new report, published Jan. 20 in the journal Nature Communicationsand offer some different ideas about how these fossils relate to ancient and modern creatures. If it is more fossilized M symmetry. In the future, the location of the species on the tree of life may finally be determined.
‘A stroke of luck’
Fossilized nervous tissue found from Cambrian eraOccurring about 543 million to 490 million years ago, Ortega Hernandez said they are “rare.” “It really is a stroke of luck.”
Scientists have uncovered the first evidence of fossilized arthropods brain From the Cambrian period about a decade ago, according to a 2012 report in the journal Nature Communications; Arthropods are invertebrates in the family Arthropoda, a group that includes modern insects, crustaceans, and arachnids, such as spiders. Since this initial discovery 10 years ago, Ortega Hernandez said, preserved nervous tissue has been found in more than a dozen Cambrian fossils, most of which are arthropods.
The fossils featured in the new study were not found on a field site, but rather deep in museum collections at Harvard University’s Museum of Comparative Zoology in Cambridge, Massachusetts, and the Smithsonian Institution in Washington, DC – Cambrian shale deposits from British Columbia.
The Harvard Fossil is approximately 0.5 inches (13 mm) long and 0.1 inches (3.5 mm) wide at its widest point. The fossil is oriented so that it looks down at the arthropods from above. On the other hand, the Smithsonian fossil provides a side view of M symmetry.; This specimen is 0.3 inches (7.5 mm) long and 0.06 inches (1.7 mm) wide.
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To the naked eye, none of the fossils look particularly exciting, Ortega Hernandez said. Of the Smithsonian’s small crater, in particular, he said, “superficially, it’s very unremarkable.” M symmetry. It has a simple exoskeleton, consisting of a head shield, segmented torso, and rear shield – somewhat similar to the exoskeleton of a pill, but long and slender.
Researchers suspect that the arthropods also had seven pairs of small appendages, two canines and six pairs of small limbs. Based on a 2019 study published in the journal temper naturewhich described a fossil of a different type in Molesonia The gender that bore these appendages. However, it is unusual to find them Molesonia Ortega-Hernandez noted that the fossils had healthy limbs, and both fossils used in the new study lacked appendages.
Despite the appearance of the fossils matte, when the Smithsonian put M symmetry. Ortega-Hernandez said he discovered something interesting under the microscope. “I realized, ‘Oh, there’s something funky inside this animal, inside this fossil,'” he said. ‘He found that each of these inconspicuous arthropods was very well preserved. The fossilized nerves look like inky black spots, because the process of fossilization has transformed tissue into organic carbon Movies.
In the Smithsonian fossil, the bulging eye of the arthropod’s head can be seen and the nerve cord can be clearly seen running along its abdomen, with some nerves protruding from its underside. In the Harvard specimen, one could see two huge orb-like eyes on the head, and a bit of a nerve cord peeking out from below the animal’s digestive system, obscuring the rest of the cord.
In both fossils, the study authors reported seeing optic nerves extending from the arthropod’s eyes to the primate body, but Strausfeld said the evidence for these nerves is “fuzzy” and, ideally, these features would be more visible. And in both samples, the authors note that there is some type of neural tissue present in the head, but it is unclear whether this structure is a brain-like synthesis or something else entirely.
“We can see something there, but we don’t have enough resolution to say, ‘Oh, it’s definitely structured this way or that way,'” Ortega Hernandez said.
Uncertainty in the data
Uncertainty in the fossil record means the exact relationship between M symmetry. Other animals also remain a mystery, Ortega Hernandez said. But based on the features in arthropods, the team built two evolutionary trees.
Both trees indicate that M symmetry. And modern chelicerates share a common ancestor, suggesting that the relatively simple nervous system of the ancient animal gave rise to the highly condensed brain seen in modern-day members of this group, such as scorpions, spiders, horseshoe crabs, and ticks. However, the trees differ in where they place other important Cambrian arthropod groups, including one known as megacheirans; These groups have nervous systems similar to modern chelates.
Depending on where on their evolutionary tree these different groups are located, their position either shows that dog-like brains evolved in a gradual manner through time, or it indicates that such nervous systems evolved independently and at different times in some modern arthropods and canals, across convergent evolutionOrtega Hernandez said.
With the data in hand, Straussfeld said he would be “cautious” about trying to put it down M symmetry. anywhere on the evolutionary tree. In order to do so, he said, he would need clearer evidence of how optic and arthropod nerves are formed (or lack thereof), as well as evidence of nerves extending to the animal’s limb roots.
“I think one needs a better preparation, a better sample” than those examined so far, Strausfeld said. “Maybe there’s another specimen lying around somewhere in the museum.”
Originally published on Live Science.