Fossilized impressions of soft-bodied organisms are exceptionally rare in coarse-grained strata. Fossilized mass-stranding events of soft-bodied organisms are even rarer. The Upper Cambrian Mt. Simon–Wonewoc Sandstone in central Wisconsin contains at least seven horizons characterized by hundreds of decimeter-sized impressions of medusae; these represent one of only two fossilized mass-stranding deposits. Medusae exhibit features nearly identical to those observed in modern scyphozoan strandings, including impressions of subumbrellar margins and gastrovascular cavities. This deposit provides insights about soft-tissue preservation in Phanerozoic marginal marine sediments, and suggests that large soft-bodied pelagic organisms were abundant in Cambrian seas.

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