Often a discovery is less about gathering new information and more about looking at something from a new perspective. That’s not always easy — except in the case of a newly described fossil sea anemone, where it was so easy to turn a putative jellyfish fossil upside down.
The fossil, first described in 1971, is famous in both scientific and amateur paleontological circles for being such an easy-to-find fossil, despite having no skeleton at all. But the creature’s story turned out to be a bizarre case of mistaken identity, scientists reported in a study published March 8 in the journal Contributions to paleontology (opens in new tab).
Formed 309 million years ago, the Mazon Creek fossil beds in Illinois provide a glimpse of aquatic species that lived during the warm, wet Carboniferous Period (358.9 million to 298.9 million years ago). At the time, the area was an estuary where muddy freshwater flowed from a river into an ocean that covered much of what is now North America. When plants and animals died in this estuary, they often quickly became covered with sediment, resulting in the proper fossilization of not only animal skeletons but also soft-bodied animals like jellyfish, which don’t usually fossilize well.
This is why Mazon Creek is so remarkable. “These fossils are better preserved than Twinkies after an apocalypse,” study co-author Jacob Hagador (opens in new tab)an expert on unusual fossil conservation at the Denver Museum of Nature and Science said in a opinion (opens in new tab). “Part of that’s because many of them dug into the ocean floor when they were buried by a stormy mudslide.” The most common fossil found in Mazon Creek is that of a bizarre jellyfish called Essexella Asherae but referred to more casually as “the Blobs” by amateur fossil hunters who have historically collected them as souvenirs.
But in 2016, Roy Plotnik (opens in new tab)Professor Emeritus of Invertebrate Paleobiology and Paleontology at the University of Chicago, noticed something was wrong E. Asherae.
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“I used to look at these jellyfish fossils and think, ‘That doesn’t look right to me,'” Plotnick, lead author of the new study, told Live Science. This lingering inkling prompted Plotnick to invite Hagadorn and Graham Young (opens in new tab)Curator of Geology and Paleontology at the Manitoba Museum in Canada to reexamine the thousands E. Asherae Fossils in the Field Museum in Chicago, as well as in other museums and private collections.
Plotnick told Live Science that Young and Hagadorn are experts on jellyfish fossils and their conservation. So if anyone had the chance to understand these creatures, they probably would.
E. Asherae looks downright bizarre compared to a stereotypical jellyfish or medusa, which many envision as a mushroom-like cap that looks like it’s molded from petroleum jelly with trailing, party-streamer-like tentacles. But not E. Asherae. Fossils suggest that instead of bearing delicate tentacles under the cap, E. Asherae rocked a membranous skirt that would make it unique, especially among modern jellyfish, all of which swim around without a skirt.
E. Asherae true nature was revealed when Plotnick and colleagues noticed that the cap did not look like a cap at all. Instead, it resembled the muscular foot that many sea anemones use to burrow into the ocean floor.
“I said, ‘Wait a minute, that looks like a sea anemone’s foot,'” Plotnick said. As he turned the specimen over, he had an epiphany: E. Asherae wasn’t a jellyfish at all. It was a bulbous sea anemone, anchoring itself to the ocean floor with its muscular foot. At the risk of oversimplifying, anemones are relatives of jellyfish, filtering their food in the water column rather than swimming through it.
Further investigation revealed that the “rock” was actually the anemone’s barrel-shaped body, with a hole at the top to allow it to suck up water for feeding. Also tiny snails that were petrified with E. Asherae were not the ancestors of modern jellyfish parasites, but rather scavengers that would bury themselves while feeding E. Asherae dead bodies, further separation E. Asherae from the jellyfish it was thought to be.
The team’s analysis showed that not only had paleontologists identified the specimen as the wrong species, they had placed it in the entirely wrong taxonomic order, the broad grouping across family and species jellyfish, to be placed in the order of the sea anemones, Actiniaria. It’s a major shift that has literally turned our understanding of this common fossil on its head.