Beached Jelly Bellies

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Science  08 Feb 2002:
Vol. 295, Issue 5557, pp. 933
DOI: 10.1126/science.295.5557.933a

Scyphozoan medusae or jellyfish are pelagic organisms that tend to congregate in near-shore, shallow water environments for reproduction, hunting, or during stormy weather. During the ebb of tides, large groups can be stranded. When a medusa realizes it is stuck in the sand, it turns belly-up and pumps its bell to try to escape, but this response only aggravates the sticky situation by filling the medusa with sand. The deceased medusa leaves a mound of sand and decomposing internal organs surrounded by concentric concave rings where it tried to repeatedly pump to flee.

Now, Hagadorn et al. have found rare and unusual traces of several strandings of large medusae from the late Cambrian, exquisitely preserved in coarse-grained sandstone beds in Wisconsin. The concentric concave rings surrounding sandy mounds, which in some cases show possible traces of internal organs, are commonly preserved on rippled bedding planes. Together, these features suggest a shallow lagoon environment, possibly a sandy barrier island, where frequent tropical storms may have caused the multiple strandings. Thus, these ancient sands provide a rare glimpse of rarely preserved soft-bodied life in Cambrian seas. — LR

Geology30, 147 (2002).

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