Tullimonstrum

Extinct genus of soft-bodied bilaterian

Tullimonstrum, commonly known as the Tully monster, is an extinct genus of soft-bodied bilaterian that lived approximately 300 million years ago during the Pennsylvanian period. It is known from the Mazon Creek fossil beds of Illinois, United States. The only known species is Tullimonstrum gregarium.

Description

Tullimonstrum was a soft-bodied creature, typically measuring about 30 to 35 centimeters in length. It had a long, segmented body with a proboscis ending in a claw-like structure with eight small teeth. The creature's eyes were set on stalks, which extended laterally from the body. The exact nature of Tullimonstrum's anatomy and its classification within the animal kingdom have been subjects of debate among paleontologists.

Discovery and Naming

The first fossils of Tullimonstrum were discovered in 1955 by Francis Tully, an amateur fossil collector, in the Mazon Creek fossil beds. The unusual nature of the fossils led to the creature being informally referred to as the "Tully monster." In 1966, the species was formally described and named Tullimonstrum gregarium by paleontologist Eugene Richardson.

Classification

The classification of Tullimonstrum has been controversial. Initially, it was difficult to place within any known group of animals. Some studies have suggested it might be related to mollusks, while others have proposed affinities with vertebrates. In 2016, a study suggested that Tullimonstrum was a vertebrate, possibly related to lampreys, based on the presence of a notochord and other features. However, this interpretation has been challenged by subsequent research.

Paleoecology

Tullimonstrum lived in a coastal estuarine environment, which was part of a large delta system during the Pennsylvanian period. The Mazon Creek area was characterized by a warm, humid climate and supported a diverse array of plant and animal life. Tullimonstrum likely occupied a niche as a predator or scavenger, using its proboscis to capture prey or feed on detritus.

Fossil Record

The fossils of Tullimonstrum are primarily found in the Mazon Creek fossil beds, which are renowned for their exceptional preservation of soft-bodied organisms. The fossils are preserved in ironstone concretions, which formed rapidly around the decaying organisms, allowing for detailed preservation of soft tissues.

Images

Fossil of Tullimonstrum gregarium

Illustration of Tullimonstrum

Another fossil specimen of Tullimonstrum

Reconstruction of Tullimonstrum as a vertebrate

Recent study illustration of Tullimonstrum

Related pages

• Mazon Creek fossil beds
• Pennsylvanian (geology)
• Vertebrate

References

• McCoy, V. E., et al. (2016). "The 'Tully monster' is a vertebrate." Nature.
• Mikami, T., et al. (2023). "New insights into the anatomy of Tullimonstrum." Journal of Paleontology.

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  Tullimonstrum gregarium fossil specimen

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  Illustration from Johnson 1969

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  Tullimonstrum gregarium fossil specimen

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  Study by McCoy et al. 2016

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  Research by Mikami et al. 2023