Hidden treasures unveiled: Flipping fossils reveals countless sea anemones in Mazon Creek

A team of paleontologists from the University of Illinois Chicago has made an exciting discovery regarding sea anemone fossils. These fossils, which have been previously misinterpreted as jellyfish, have been hiding in plain sight for nearly 50 years. By simply turning the ancient animals upside down, the researchers realized that the fossils were actually anemones.

The fossils were found in the Mazon Creek fossil deposits of northern Illinois, which is known for its exceptional preservation of soft-bodied organisms. The fossils in this area are incredibly well-preserved due to the rapid burial of millions of anemones and other animals in muddy sediments caused by an ancient delta.

The most common fossil found in the Mazon Creek deposits, referred to as “the blob” by local fossil collectors, was often overlooked or discarded due to its nondescript appearance. These blobs were so abundant that they were sold for a few dollars at local flea markets. However, many of these specimens were eventually donated to museum collections by avocational collectors.

In 1979, a professor named Merrill Foster studied these blobs and concluded that they were jellyfish, naming them Essexella asherae. He identified a unique feature—a tough “curtain” hanging off the umbrella-like bell of the jellyfish, which resembled a skirt enclosing their arms and tentacles. This feature contributed to their barrel-like shapes.

Upon reexamining thousands of museum specimens in their new study, the paleontologists realized that the fossils were not jellyfish but rather anemones. By turning the fossils upside down, they observed that the “bell” was actually an expanded muscular foot that the anemone used to burrow into the seafloor. The tough “curtain” was the barrel-shaped body of the anemone.

The researchers also discovered another fossil jellyfish species that, when examined closely, turned out to be rare anemones compressed from top to bottom. Some of the exceptionally preserved fossils even revealed the muscles that the anemones used to bend and contract their bodies.

The wide variety of preservation seen in the Essexella specimens was attributed to the different durations that dead anemones remained on the seafloor before being buried. Additionally, the researchers clarified that a common trace fossil believed to be an anemone burrow from the same period was likely made by an animal similar to Essexella. The team speculated that due to the abundance of Essexella fossils, these anemones may have lived in large groups on the sea floor.

This study highlights the importance of reevaluating and challenging previous interpretations in paleontology. By shifting their perspective, the researchers were able to uncover a significant collection of sea anemone fossils that had been misidentified for decades.

Source: University of Illinois at Chicago

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