This is Mazon Monday post #155. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
-----------------------------------------------------
If you are a collector (or just a fan) of Mazon Creek fossils, you've probably heard of the (somewhat controversial) work of Roy Plotnick's work to reclassify Essexella asherae from a jellyfish to a sea anemone. Roy is a long time ESCONI member and professor emeritus of earth and environmental sciences at the University of Illinois at Chicago. He did a presentation on E. asherae for the ESCONI Mazon Creek Open House back in October 2022.
We looked at Essexella way back in Mazon Monday #14. It was described by Bradley University professor Merrill Foster in 1979 in his paper titled "Soft-bodied coelenterates in the Pennsylvanian of Illinois". That paper was included in the book "Mazon Creek Fossils", which was edited by M. H. Nitecki (see Mazon Monday #42).
Roy's paper "An abundant sea anemone from the Carboniferous Mazon Creek Lagerstӓtte, USA" was published last week in the journal Papers in Paleontology. He and is coauthors (Graham Young and James Hagadorn), worked long and hard to provide evidence for their theory of this problematic animal.
Abstract
Sea anemones (Actiniaria) are among the rarest of recognized fossil organisms, even rarer than jellyfish. Here we demonstrate that the most abundant fossil in the Pennsylvanian Mazon Creek Lagerstätte of Illinois, Essexella asherae, is an infaunal or semi-infaunal anemone. Essexella is redescribed based on a taphonomic analysis of thousands of specimens, as well as associated medusae and trace fossils. Specimens of Essexella (also known as the ‘blobs’) were long believed to be medusae, but we reassign Essexella to the order Actiniaria and reinterpret the putative jellyfish Reticulomedusa as the pedal or oral disc of Essexella. We also implicate Essexella as a producer of Conostichus, a widespread plug-shaped trace fossil that occurs in coeval strata in the same region. Radiate structures comparable to the bases of Conostichus and the ichnofossil Bergaueria, as well as the pedal discs of modern anemones, characterize Reticulomedusa. Bona fide medusae are present in the Mazon Creek biota, and include Anthracomedusa turnbulli and Octomedusa pieckorum, whereas the soft-bodied fossil Lascoa mesostaurata is referred to Problematica.
Phys.org has a nice summary of the paper.
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.
"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.
"These fossils are better preserved than Twinkies after an apocalypse. 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.