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Location
The three geologists discovered the Late Cambrian fossilized jellyfish in the Krukowski Quarry near Mosinee in central Wisconsin. The fossils were in sandstone being quarried for use as commercial flagstone. The deposit is referred to as Mt. Simon-Wonewoc Sandstone. The jellyfish fossils were discovered in seven rock layers which extend vertically for twelve feet.
Size
There were more than 100 jellyfish fossils found, and many are over 50 cm in diameter, five times the size of jellyfish fossils found elsewhere. The largest of the specimens have bells which measure up to one meter, or about three feet, across. In another strata of the sandstone, smaller jellyfish fossils were discovered.
Geologic History
Geologists Damrow, Dott and Hagadorn concluded that the jellyfish died in at least seven mass deaths due to stranding over a period of one million years. Geologists who have studied the fossil imprints estimate this may have happened about 525 million years ago. They believe the area was the site of inland seas with tides which covered the sand flats with shallow water. The rippled surfaces of the seven planar layers suggests water action.
Significance
The Wisconsin jellyfish fossils are significant because very few jellyfish fossils have been discovered from the Cambrian time period. Even rarer are jellyfish fossils preserved in the type of coarse-grained sandstone which exists in the Krukowski Quarry area. They are also the largest specimens of fossilized jellyfish found to date, according to Hagadorn.