Fossil Discovery: First-Ever Silurian Horseshoe Crab Unearthed

Speedy Summary

• Horseshoe crabs, aquatic chelicerate arthropods with an evolutionary history of 450 million years, are considered “living fossils.”
• A new Silurian-age species of horseshoe crab, Ciurcalimulus discobolus, was recently described by Dr. James Lamsdell from West Virginia University.
• This species bridges an 80-million-year gap in the fossil record between Ordovician (480-450 million years ago) and Late Devonian (370 million years ago) specimens.
• The fossil was discovered in Indiana, USA, from a rock formation dating back approximately 424 million years.
• Unlike other early horseshoe crabs like Lunataspis, Ciurcalimulus discobolus has distinct morphological traits such as the absence of axial nodes on its thoracetron and lacking a thoracetron marginal rim defined dorsally by a furrow.
• The study suggests that horseshoe crabs survived the end Ordovician mass extinction with limited evolutionary impact and retained similarities to earlier forms for extended periods.
• Horsecrab origins appear centered in Lauriea (North America/Europe),though paleontological research historically is biased toward these regions over gondwana.

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