Horseshoe crabs, or xiphosurans, are an order of marine and brackish water arthropods. Despite their common name, they are not really crabs, and are more closely related to spiders and scorpions.
“Xiphosurans are aquatic chelicerate arthropods with an extensive fossil record stretching back to the Ordovician, but a seemingly low standing diversity with only 76 species described to date throughout the entirety of their 445-million-year evolutionary history,” said lead author Dr. James Lamsdell, a paleontologist in the Department of Geology and Geography at West Virginia University, and his colleagues.
“Despite being rare components of aquatic ecosystems, the four extant horseshoe crab species have long been recognized as being biomedically important for vaccine production and keystone components of their ecosystems in need of active conservation, and are the focus of extensive research.”
The newly-identified xiphosuran species lived in what is now Canada during the Sandbian age of the Ordovician period, between 458 and 453 million years ago.
Named Lunataspis borealis, it had a number of traits considered diagnostic of the genus Lunataspis, including a large, lunate carapace.
“The discovery demonstrates that multiple Lunataspis species occupied the shallow seas of Laurentia during the Late Ordovician,” the paleontologists said.
Three specimens of Lunataspis borealis were recovered from the Gull River Formation, where it is exposed in the north face of an inactive quarry in Kingston, Ontario, Canada.
“The holotype specimen is a mostly complete adult individual while the two paratypes are juveniles or subadults preserving the prosoma and thoracetron along with parts of the postabdomen,” the researchers said.
“Lunataspis borealis provides critical insight into the ontogeny and morphology of the earliest horseshoe crabs, indicating that at least some Paleozoic forms had freely articulating tergites anterior to the fused thoracetron and an opisthosoma comprising 13 segments.”
A paper on the findings appears in the Geological Magazine.
James C. Lamsdell et al. A new species of the Ordovician horseshoe crab Lunataspis. Geological Magazine, published online October 5, 2022; doi: 10.1017/S0016756822000875
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