A 500-million-year-old spider relative grows claws where they shouldn’t.

The fossils were not noticeable at all. This first occurred to Harvard paleontologist Rudy LeRochy-Aubril while examining arthropod fossils dating back to the Cambrian period (538.8 million to 485.4 million years ago).

“But when I prepared it, it unexpectedly revealed exquisitely preserved limbs, including a pair of frontal claws protruding from the head,” says Lillocy-Aubril. popular science.

Early arthropod specimens lack such claws. Instead, Cambrian arthropods usually have antennae in that position. In other words, the nails that Lerosie-Aubril was looking at were do not have It should be there.

This humble fossil Megachelyserax custoia 500 million year old marine predator. The fossil, first unearthed over 40 years ago in the deserts of western Utah, is the oldest known chelicodont (a group of arthropods that includes modern animals). spiderscorpions, horseshoe crabs, and sea spiders. This bizarre specimen stretches the evolutionary history of chelicerates back 20 million years and helps explain the evolution of claws. This finding is detailed in a study published today in the journal nature.

The nails have arrived

LeRochy Aubril, co-author of the new study, spent more than 50 hours cleaning. M. Kustoy Peek at the fossil under a microscope and study its amazing anatomy. Its body is just over 3 inches long and has a single upper head shield and an exoskeleton consisting of nine separate body parts.

“Appendages under the head are adapted for feeding and sensory functions, while appendages along the trunk are used for breathing and swimming,” Lerosy-Aubril explains. “This level of anatomical specialization is surprisingly advanced for an arthropod of this age.”

Chelicerate arthropods have a body divided into an upper cephalothorax and a lower abdomen, and have four pairs of walking legs, two anterior chelicerae and palpable limbs for grasping objects. Prior to this discovery, the oldest known cheliceriform arthropods date back approximately 480 million years. M. Kustoy lived 20 million years ago, making it the oldest known branch of the chelicodont family tree. There are currently more than 120,000 species of chelicerates, including spiders and horseshoe crabs.

just keep digging

Despite the fossil’s age, Relocy Aubril was surprised by how modern it looked. M. Kustoy It looks different compared to animals that lived at the same time, such as the trident-wielding trilobite.

“Apart from a few obvious features of antiquity, this 500-million-year-old chelidae would fit perfectly into today’s oceans,” he says.

M. Kustoy It is also an important transitional species, bridging the gap between Cambrian arthropods, which lacked proclaws, and much younger, horseshoe crab-like chelicerae, which did have claws.

Until now, scientists weren’t sure about the order in which claws and bodies with two regions that perform specific functions first evolved. M. Kustoy These head appendages have been shown to have evolved before disappearing and resembling today’s spider legs.

“This was a reconciliation of several competing hypotheses, and in a sense, everyone was partially right,” study co-author Javier Ortega Hernández, curator of invertebrate paleontology at Harvard University’s Museum of Comparative Zoology, explained in a statement.

Megachelyserax custoi It is named after the famous French explorer Jacques-Yves Cousteau, whose documentary and environmental advocacy inspired generations of exploration. LeRochy-Aubril says the fossils themselves are also a reminder to keep digging.

“This particular fossil was discovered by a dedicated professional paleontologist. [Lloyd Gunther] “Fossils are found in most parts of the United States. Fossils are found in most parts of the United States. Get out and explore and find out what stories are hidden in the rocks around you,” he says.