Photos: Ancient Tully Monster's Identity Revealed

One odd-looking creature

Tully monster

(Image credit: Sean McMahon | Yale University)

Since the so-called Tully monster's discovery in 1958, fossils of the odd-looking creature have mystified scientists. Now, two 2016 studies using cutting-edge technologies and a team of collaborative experts have announced that the approximately 307-million-year-old fossils — which, incidentally, are the state fossil of Illinois — are vertebrates. one study found that they were are jawless fish, similar to modern lampreys.

The other found that they were vertebrates, and likely "a type of very weird fish."

Tully monster, envisioned

Tully monster

(Image credit: Sean McMahon | Yale University)

An illustrator's interpretation of the Tully monster (Tullimonstrum gregarium). Notice its hammerheadlike eyes and its toothy mouth at the end of its proboscis.

Fishy swimmer

Tully monster

(Image credit: Sean McMahon | Yale University)

The Tully monster likely used its tail to propel it forward in the water.

First Tully monster fossil

Tully monster

(Image credit: Nicole Karpus)

The first fossil ever found of the Tully monster. Notice its proboscis folded over its head at the top.

Open wide

Tully monster

(Image credit: Nicole Karpus)

The toothy mouth at the end of the long proboscis. The dark spot on the right might be the remnants of an organ, the researchers said.

Eye bar

Tully monster

(Image credit: Nicole Karpus)

A sideways view of a Tully monster specimen. Notice its long eye bar pointing diagonally on the right side of the fossil.

Folded tail

Tully monster

(Image credit: Nicole Karpus)

A fossil with a folded tail, with the dorsal fin extending from the fifth skeletal muscle in the middle of the specimen.

Oh, that face!

Tully monster

(Image credit: Nicole Karpus)

This specimen shows a clear view of the Tully monster's eyes (right), proboscis (middle) and mouth (left).

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It's all in the eyes

Tully monster eyes

(Image credit: University of Leicester)

An microscopic image of Tully monster's peculiar eyes.

Tully Hunt

Tully hunt

(Image credit: University of Leicester)

Thomas Clements and Sarah Gabbott search for the Tully monster in Illinois, where Tully is the state fossil.

A star is born

U-haul truck

(Image credit: University of Leicester)

The Tully Monster is so famous in Illinois, that it's even featured on U-Haul trucks.