No doubt it was a strange sight, alien looking even. Over three-hundred million years ago, a one-foot mass swam the oceans. Its eyes were jutted out from its sides, perched at the ends of a bar like a hammerhead shark’s eyes. Its teeth were situated at the end of a trunk-like appendage. The tail had horizontal fins, reminiscent of a squid in their shape.
Fossils within concretions are the only evidence scientists have of this creature—Tullimonstrum gregarium, colloquially known as the Tully Monster.
The Tully Monster was shrouded in mystery for more than 50 years following its initial discovery. Now, a team of paleontologists has provided some insight into this creature. Their research was published March 16 in Nature.
The Tully Monster was first discovered by its namesake Francis Tully in 1958 in the Mazon Creek fossil beds of Illinois, according to the Illinois State Museum. It was described a little under a decade later by Eugene Richardson, who bequeathed its scientific name. Many more fossil specimens of the creature were excavated following its initial discovery, and the creature gained some notoriety. In 1989, the Tully Monster became the Illinois State Fossil.
“I was first intrigued by the mystery of the Tully Monster,” said Victoria McCoy, the study’s lead author, in a statement. “With all of the exceptional fossils, we had a very clear picture of what it looked like, but no clear picture of what it was.”
Over the years, the creature has been compared to nemerteans, polychaetes, gastropods, conodonts, and the stem group arthropod Opabinia.
Based on a morphological review of more than 1,200 specimens, the researchers placed the Tully Monster in the stem lineage of lampreys, Petromyzontida. The analysis characterized the creature as a vertebrate with gill pouches and a notochord, which acted as a spinal cord.
“It’s so different from its modern relatives that we don’t know much about how it lived,” McCoy added in a statement. “It has big eyes and lots of teeth, so it was probably a predator.”
Even details regarding the species’ first appearance and extinction remain in question, according to Yale University. And the fossil beds of Illinois remain the only place in the fossil record where Tully Monster specimens have been found.
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