Unveiling the Mystery: This 300-Million-Year-Old Fossil Baffles Experts with Its Unprecedented Origins!

The Tully monster, or Tullimonstrum gregarium, was first found in the Mazon Creek fossil beds of Illinois in 1955. This unusual creature roamed our planet around 300 million years ago, long before dinosaurs existed. Despite numerous studies, scientists still debate its classification within the tree of life.

Amateur fossil collector Francis Tully made the initial discovery near Chicago. Fascinated by its striking appearance, he took it to the Field Museum for an expert opinion. Museum staff, including Eugene S. Richardson Jr., struggled to categorize it and later admitted it was difficult to even determine which phylum it belonged to. It wasn’t until 1966 that the Tully monster was formally named, reflecting both its commonality in the region and honoring its discoverer.

For years, theories about the Tully monster’s classification have varied widely. Some researchers believed it might be a segmented worm, while others thought it could be a type of mollusk or even an arthropod. In a noteworthy 2016 study, paleobiologist Victoria McCoy suggested that the Tully monster might actually be a vertebrate related to jawless fish like lampreys. She pointed to a primitive spinal structure, the notochord, as evidence. This claim excited many in the scientific community, sparking conversations around this enigmatic creature.

However, skepticism arose when subsequent studies indicated that some supposed vertebrate features could also appear in cephalopods, such as squids, under certain conditions. This raised eyebrows about the validity of McCoy’s conclusions.

In 2023, new research led by Tomoyuki Mikami at the University of Tokyo re-examined the creature using advanced 3D laser scanning. Their findings suggested that the Tully monster may actually be an invertebrate chordate, similar to modern sea squirts. This challenges previous vertebrate claims and adds another layer to the creature’s mystery. Despite these findings, McCoy still holds onto her original hypothesis, acknowledging that the large, complex eyes of the Tully monster are hard to explain with the new theory.

The Tully monster’s fossilization process makes it tough to ascertain its true nature. The Mazon Creek beds preserve many fossils but often lack the fine details needed for a clearer understanding of internal structures, such as muscles or soft organs. McCoy notes that if more organ details were available, it could greatly aid classification efforts.

What makes the Tully monster especially intriguing is its relatively recent existence during the Carboniferous period. Unlike other ancient fossils that defy classification from even earlier eras, this creature’s age raises questions about why it remains unclassified. As McCoy says, “It’s unusual for a fossil 300 million years old to be so mysterious.” Scientists are hopeful that future discoveries will help clarify where the Tully monster fits in the vast mosaic of life on Earth.

For further reading on the Tully monster, check out the 2016 study in Nature here for an in-depth look at its vertebrate claims.

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