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. Artwork by Julius Csotonyi.
(Winnipeg, Manitoba: March 9, 2023) – When you think of the Manitoba Museum, perhaps you imagine the large walk-through dioramas, or the Hudson’s Bay Company ship Nonsuch. But the Museum also holds many collections, and some of those are helping us to solve longstanding scientific questions.
An example of this is shown in a newly-published paper in the scientific journal Papers in Palaeontology, written by a team of scientists including Dr. Graham Young, the Museum’s Curator of Geology & Paleontology. The team examined many hundreds of specimens from several museums, including the Manitoba Museum, in order to re-interpret one of the most abundant fossils in North America: the Mazon Creek “blobs,” strange fossils that have been given the scientific name Essexella asherae.
Young is an expert on fossil jellyfish, and became involved in the study of “blobs” through a chance discussion on social media. Plotnick had posted a photo of one of these strange fossils, which have been considered to be “fossil jellyfish” since the 1970s. Young assured him that it was not a jellyfish, but didn’t know what it actually was, and this scientific study developed from the ensuing question – what was Essexella, really?
A thorough re-assessment by Young and his colleagues took several years, and resulted in a reconstruction of the fossils as sea anemones, effectively “turning the blobs upside down.” Billions of sea anemones adorn the bottoms of the world’s oceans, yet they have always been considered among the rarest of fossils, because their squishy bodies lack easily-fossilized hard parts. Young and his colleagues Dr. Roy Plotnick and Dr. James Hagadorn have thus discovered that countless sea anemone fossils have been hiding in plain sight for decades.
These strange 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 animals were buried in rapidly-deposited muddy sediments.
“By far the most common fossil at Mazon Creek is the form known to local recreational fossil collectors as “the blob,” according to lead author Roy Plotnick. Plotnick notes that such blobs were so common and often nondescript that many were discarded or sold for a few dollars at local flea markets. Nevertheless, over the years, collectors have donated many hundreds of them to museum collections. Young notes that the Manitoba Museum is fortunate to have a good collection of unusual Mazon Creek fossils, donated by long-time volunteer Ed Dobrzanski, and these include blobs in addition to other unusual fossils such as worms and shrimp.
In 1979, a professor in Illinois made the first detailed study of the blobs. He decided that they were fossil jellyfish and named them Essexella asherae. He reported that these jellyfish had a unique feature found in no living jellyfish, a tough “curtain” that hung off its umbrella-like bell (the top part of a jellyfish), akin to a skirt that enclosed the arms and tentacles, accounting for the barrel-like shape. In their new paper, the paleontologists took a fresh look at Essexella by examining thousands of museum specimens.
“It quickly became obvious that not only it wasn’t a jellyfish, but turned upside down it was clearly an anemone, probably one that burrowed into the seafloor. The ‘bell’ was actually an expanded muscular foot used to wiggle the anemone into the seafloor,” Plotnick said.
The tough “curtain” was the barrel-shaped body of the anemone. Another so-called fossil jellyfish species that looked like a daisy turned out to represent rare anemones squashed from top to bottom, like one might stomp an aluminum can.
“These fossils are remarkably preserved. In part that’s because many of them burrowed into the seafloor as they were being buried by a stormy avalanche of mud,” said study co-author James Hagadorn, an expert on unusual fossil preservation at the Denver Museum of Nature and Science.
“Although most of these fossils are preserved as decomposing blobs, some specimens are so superbly preserved that we can even see the muscles that the anemones used to bend and contract their bodies,” said Young. The researchers explain that the wide variety of preservation seen in Essexella specimens was due to the different durations that dead anemones sat on the seafloor before burial.
“This sort of study allows the Manitoba Museum to contribute to the global progress of science, through our expertise and collections,” said Young. “It is also of considerable benefit to us, as we learn so much by working with outside experts and carrying out detailed analyses.”
In the case of the Mazon Creek Essexella, the fresh knowledge gained from this study will be very useful to Young as he continues to study some very abundant and quite diverse fossil jellyfish from northern Manitoba.
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