At first, Lerosey-Aubril considered the fossil rather unremarkable, but after uncovering a pair of frontal claws in place of expected sensory antenna his assessment suddenly changed \u2013 this was a chelicerate and based on the Cambrian age of the fossil, the oldest of its kind ever found.<\/p>\n
\u201cClaws are never in that location on a Cambrian arthropod. It took me a few minutes to realise the obvious, I had just exposed the oldest chelicerate ever found,\u201d said Lerosey-Aubril, the lead author of a\u00a0study published last week in\u00a0Nature<\/a> describing\u00a0M.cousteaui. \u201cThis fossil documents the Cambrian origin of chelicerates and shows that the anatomical blueprint of spiders<\/a> and horseshoe crabs<\/a> was already emerging 500 million years ago.\u201d<\/p>\n After more than 50 hours of careful cleaning and meticulous preparation underneath a microscope, Lerosey-Aubril revealed other, finer elements of\u00a0M.cousteaui\u2019s anatomy, including a dorsal exoskeleton<\/a> consisting of a horseshoe-shaped head shield and nine separate body segments. He also found evidence of plate-like respiratory structures beneath these body segments that look remarkably similar to the book gills of modern horseshoe crabs.<\/p>\n Undoubtedly, the most characteristic feature of\u00a0M.cousteaui\u00a0is the pair of \u201cmassive, three-segmented chelicerae\u201d projecting from its head. These grasping appendages are pincer-like and help identify M.cousteaui\u00a0as an unequivocal chelicerate, rather than another type of arthropod.<\/p>\n The Cambrian has a rich arthropod fossil record, but until now no unambiguous chelicera-bearing arthropod from this period had been found. Prior to the discovery of\u00a0M.cousteaui, the oldest confirmed chelicerates dated to the Early Ordovician of Morocco, roughly 480 million years ago.<\/p>\n The existence of this remarkable species 20 million years earlier places it near the base of the chelicerate family tree and informs researchers that the development of chelicerae occurred early, before several other key characters that define the group.\u00a0<\/p>\n \u201cMegachelicerax\u00a0shows that chelicera and the division of the body into two functionally specialised regions evolved before the head appendages lost their outer branches and became like the legs of spiders today,\u201d explained co-author Javier Ortega-Hern\u00e1ndez. \u201cThis tells us that by the mid-Cambrian, when evolutionary rates were remarkably high, the oceans were already inhabited by arthropods with anatomical complexity rivalling modern forms.\u201d<\/p>\n Today, chelicerates comprise more than 120,000 species, from spiders and scorpions to mites, horseshoe crabs and sea spiders<\/a>. Behind insects<\/a>, they are the second-most diverse group of arthropods, inhabiting both terrestrial and aquatic ecosystems.<\/p>\n However, during the Cambrian and the Ordovician, chelicerates were confined to the water and, despite the early acquisition of a relatively complex anatomy, they were ecologically overshadowed by seemingly simpler arthropod groups like trilobites. It wasn\u2019t until the Silurian, approximately 430 million years ago, that the group successfully spread to the land.<\/p>\n \u201cA similar evolutionary pattern has been documented in other animal groups,\u201d said Lerosey-Aubril. \u201cThis shows that evolutionary success is not only about biological innovation – timing and environmental context matters.\u201d<\/p>\n More amazing wildlife stories from around the world<\/p>\n","protected":false},"excerpt":{"rendered":"More than 40 years after it was discovered in a desert in western Utah, an unassuming fossil has…\n","protected":false},"author":2,"featured_media":522548,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[59,90,56,54,55],"class_list":{"0":"post-522547","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-gb","9":"tag-science","10":"tag-uk","11":"tag-united-kingdom","12":"tag-unitedkingdom"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/posts\/522547","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/comments?post=522547"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/posts\/522547\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/media\/522548"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/media?parent=522547"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/categories?post=522547"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/tags?post=522547"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"Megachelicerax](\"https:\/\/www.newsbeep.com\/uk\/wp-content\/uploads\/2026\/04\/Megachelicerax-cousteaui-scaled.jpeg\")
The holotype of M.cousteaui, showing its body segments and distinctive, grasping chelicerae. Credit: Rudy Leroseu-Aubril<\/p>\n![\"Megachelicerax](\"https:\/\/www.newsbeep.com\/uk\/wp-content\/uploads\/2026\/04\/Megachelicerax-cousteaui-1-scaled.jpeg\")
The newly discovered chelicerate M.cousteaui looks like a cross between a horseshoe crab and a woodlouse. Credit: Masato Hattori\/Harvard University<\/p>\n![\"Modern-day](\"https:\/\/www.newsbeep.com\/uk\/wp-content\/uploads\/2026\/04\/Modern-day-spider-with-Megachelicerax-cousteaui-scaled.jpeg\")
The holotype of M.cousteaui lying next to a living relative. Credit: Rudy Lerosey-Aubril<\/p>\n