The progenitor of spiders, scorpions, and horseshoe crabs has recently been identified as a segmented little beastie that lived in the waters some half a billion years ago.
Setapedites abundantis is the name of this minuscule species, measuring about 5 millimeters in length, that lived 478 million years ago in an ocean that spanned what is now Morocco.
After examining its fossils for over 20 years, paleontologists have now determined that it is a member of the Euchelicerata group of arthropods.
“Initially, we only intended to describe and name this fossil. We had absolutely no idea that it would hold so many secrets,” According to Swiss paleontologist Lorenzo Lustri of the University of Lausanne.
“It was therefore an exhilarating surprise to realize, after careful observations and analysis, that it also filled an important gap in the evolutionary tree of life.”
Setapedites abundantis as seen by the artist. (Sorojsrisom, Lisa)
The group of invertebrates known as arthropods, which includes insects, myriapods, crustaceans, and arachnids, is extremely abundant and diverse, making up around 75% of all animal species on Earth. There are subgroups within this group. Chelicerates are arthropods with chelicerae, which are mouthparts that resemble pincers or fangs and are used to seize and poison victims.
In addition to numerous extinct groups, including sea scorpions, this category includes spiders, mites, ticks, scorpions, horseshoe crabs, and ticks. However, the precise moment and mechanism of these various creatures’ divergence and the beginning of their own evolutionary journey apart from the other arthropods remain unknown.
Early in the new millennium, Setapedites abundantis was discovered in Morocco’s Fezouata Shale formation. Although it was the most prevalent kind of fossil in the species, it took some time for researchers to get to it because it requires a lot of effort to examine and characterize fossils.
Lustri and his associates examined multiple fossilized specimens of the organism, which were superbly conserved in the silky, thin shale that had acted as silt on the ocean floor. Additionally, they discovered biramous, or two-branched, appendages on the animal’s back.
The researchers were able to firmly identify the species as belonging to the family Offacolidae thanks to these appendages and their placement. Offacolus kingi is the only other species in this genus, and it lived between 444 and 420 million years ago during the Silurian period.
Setapedites abundantis now stands in for the earliest known member of this specific branch of the arthropod family tree, bridging the void between early arthropods and Euchelicerata, since Offacolidae are euchelicerates.
As of right now, the location of the fossil is known. The next stage involves more research to gain a deeper understanding of its distinctive characteristics’ genesis and evolution, and ultimately how our beloved spider species came to be.
