Undescribed Horseshoe Crab Ancestor

with Soft Tissue Preservation

Aff Cyamocephalus sp

Phylum Arthropoda, Subphylum Chelicerata, Class Merostomata, Order Synziphosurida

Geological Time: Early Silurian (Llandoverian Stage)

Size (25.4 mm = 1 inch): Fossil is 30 mm long (with telson) by 15 mm wide on an 65 mm by 65 mm matrix

Fossil Site: Jupiter Formation (?), Lac Simard, Quebec, Canada

Fossil Code: MMT179

Price: Sold

Fossil Horseshoe Crab Ancestor Description: This arthropod is a member of the Synziiphosurida. These ancient arthropods resemble the modern-day horseshoe crabs referred to some as “living fossils” due to the fact that they have changed but little over time. This one is in excellent shape, showing detail of the prosoma (head), opisthosoma (abdomen) and telson (tail). Interestingly enough, there are vestiges of anetennae prorturuding from the leading edge of the prosoma, a feature unknown in the Xiphosuida proper. It looks much like the genus Cyamocephalus from the contempry Silurian deposits of Scotland, but is as yet undescribed. To my knowledge it is the only such example known from eastern Canada, and the only such specimen to show soft tissue preservation. I have included a life retoration of Cyamocerphalus from Scotland for comparison purposes.

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