We Might Have Been Wrong About Where Spiders Came From
A new study published today in Current Biology challenges the popular conception that spiders first emerged on land, instead suggesting that these arachnids and their relatives originated and evolved in the ocean. The team reached this conclusion by investigating the fossilized central nervous system of Mollisonia symmetrica, a long-extinct animal from the Cambrian era (between 540 and 485 million years ago), thought to be the ancestor of horseshoe crabs. Mollisonia's brain structure closely resembled that of modern spiders and their relatives, not their supposed crab descendants.
'The discovery of an arachnid brain in such an ancient creature as Mollisonia suggests that the major groups of arthropods alive today were already established then,' Nick Strausfeld, study lead author and neuroscientist at the University of Arizona, told Gizmodo in an email. He added that this 'casts a fresh view on the question: Where did arachnids first evolve?'
Until now, scientists had assumed—based on the external features of arachnid-like fossils found in sedimentary rocks formed on land—that modern spiders and their relatives evolved on land. For the study, however, Strausfeld and his colleagues looked inside a well-preserved fossil of Mollisonia, which they did using an optical microscope and other imaging techniques to investigate its cerebral arrangements in higher detail.
The team uncovered several similarities between modern spiders and Mollisonia, but the most striking feature was that of the creatures' central nervous system. Unlike insects, arachnid brains have a strange backward structure, in which the 'forebrain lies on top of circuits that control the movement of the legs,' Strausfeld explained. It's this that makes spiders and their relatives so 'incredibly versatile in their movements.' As the new research shows, 'the backward organization is enough of a 'tell' to demonstrate [that] Mollisonia's brain arrangement typifies those of living arachnids,' he said.
Other common features the team found included external resemblances, such as jointed limbs or pincer-like claws. They bolstered their hypotheses by running a statistical analysis comparing 115 anatomical traits across both living and extinct arthropods (which includes arachnids), which placed Mollisonia as a 'sister' to modern arachnids, the authors reported in the study.
'This is very interesting, but we do not yet know how it relates to the vast array of arachnids other than spiders,' said Paul Selden, a paleontologist and arachnologist at the University of Kansas who wasn't involved in the new work, in an email to Gizmodo. 'Clearly, their conclusions on the phylogenetic [study of evolutionary history using visual cues] placement of Mollisonia are fascinating but merely mark the start of further investigation.'
It's probably premature to declare spiders as spawns of the sea, but the good news is that Strausfeld and his colleagues already seem to be on the case.
'Most Cambrian fossils look very different from modern species, so it is really exciting when such outward appearances reveal something inside them—a fossilized brain and nervous system—that tells a different story,' Strausfeld said. 'Arachnids are a crucial feature of our biosphere, and we should pay attention to what they contribute to our well-being.'
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Hidden threats YR4 was detected by the Asteroid Terrestrial-impact Last Alert System, or ATLAS telescope, in Río Hurtado, Chile, two days after the asteroid had already made its closest pass by Earth, hidden by the bright glare of the sun as it approached our planet. The same thing occurred when an asteroid measuring roughly 20 meters (about 65 feet) across hit the atmosphere and exploded above Chelyabinsk, Russia, on February 15, 2013, damaging thousands of buildings, according to the European Space Agency. While no one died, about 1,500 people were injured when the windows in homes and businesses blew out due to the shock wave. Trying to observe asteroids is challenging for many reasons, Rivkin said. Asteroids are incredibly faint and hard to see because rather than emitting their own light, they only reflect sunlight. And because of their relatively tiny size, interpreting observations is not a clear-cut process like looking through a telescope at a planet such as Mars or Jupiter. 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'NEOMIR would have detected asteroid 2024 YR4 about a month earlier than ground-based telescopes did,' said Richard Moissl, head of ESA's Planetary Defence Office, in a statement. 'This would have given astronomers more time to study the asteroid's trajectory and allowed them to much sooner rule out any chance of Earth impact in 2032.' NASA and other space agencies are constantly on the lookout for potentially hazardous asteroids, defined as such based on their distance from Earth and ability to cause significant damage should an impact occur. Asteroids that can't get any closer to our planet than one-twentieth of Earth's distance from the sun are not considered to be potentially hazardous asteroids, according to NASA. When the new Vera C. Rubin Observatory, located in the Andes in Chile, released its first stunning images of the cosmos in June, researchers revealed the discovery of more than 2,100 previously unknown asteroids after seven nights of observations. Of those newly detected space rocks, seven were near-Earth objects. A near-Earth object is an asteroid or comet on an orbit that brings it within 120 million miles (about 190 million kilometers) of the sun, which means it has the potential to pass near Earth, according to NASA. None of the new ones detected by Rubin were determined to pose a threat to our planet. Rubin will act as a great asteroid hunter, de Wit said, while telescopes such as Webb could be a tracker that follow up on Rubin's discoveries. A proposal by Rivkin and de Wit to use Webb to observe YR4 in the spring of 2026 has just been approved. Webb is the only telescope with a chance of glimpsing the asteroid before 2028. 'This newly approved program will buy decision makers two extra years to prepare — though most likely to relax, as there is an 80% chance of ruling out impact — while providing key experience-based lessons for handling future potential impactors to be discovered by Vera Rubin,' de Wit said. And because of the twists and turns of YR4's tale thus far, asteroids that have potential to affect the moon could become objects of even more intense study in the future. 'If this really is a thing that we only have to worry about every 5,000 years or something, then maybe that's less pressing,' Rivkin said. 'But even just asking what would we do if we did see something that was going to hit the moon is at least something that we can now start thinking about.'
