Emeritus Professor Roy Plotnick Flips the Script on Anemone Fossils

“Death and decay in the Pennsylvanian”: A doomed cluster of the sea anemone Essexella is inundated by an underwater sediment avalanche, which kills and buries them. A previously killed anemone lies rotting on the sea floor, while the jellyfish Anthracomedusa and Octomedusa, soon to also be buried, swim above.

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Billions of sea anemones adorn the bottom of the Earth’s oceans — yet they are among the rarest of fossils because their squishy bodies lack easily fossilized hard parts. Now a team of paleontologists has discovered that countless sea anemone fossils have been hiding in plain sight for nearly 50 years.

In a newly published paper in the journal Papers in Palaeontology, University of Illinois Chicago’s Roy Plotnick and colleagues report that fossils long-interpreted as jellyfish were anemones. To do so, they simply turned the ancient animals upside down.

Essexella, a 310-million-year-old fossil sea anemone from Illinois.
Credit: Papers in Palaeontology

“Anemones are basically flipped jellyfish. This study demonstrates how a simple shift of a mental image can lead to new ideas and interpretations,” said Plotnick, UIC professor emeritus of earth and environmental sciences and the study’s lead author.

The fossils come from the 310-million-year-old Mazon Creek fossil deposits of northern Illinois. Mazon Creek is a world-famous Lagerstätte, a term used by paleontologists to describe a site with exceptional fossil preservation. An ancient delta allowed the detailed preservation of the Mazon Creek soft-bodied organisms because millions of anemones and other animals were rapidly buried in muddy sediments.

Read more:

WTTW - Fossil Discovery in Northern Illinois Has Turned Science on Its Head

Popular Mechanics - Rare anemone fossils found in plain sight

Live Science - Oops, this 300 million year old "blob" fossil was upside down. It's not a jellyfish after all