In collaboration with researchers at Stanford University, UChicago paleontologists have discovered a fossilized ancestor of the modern-day hagfish, which has confirmed the latter’s supposed phylogeny, lineage, and surrounding diversification.

The 12-inch Tethymyxine tapirostrum fossil from the Cretaceous period has filled a 100 million–year gap in the fossil record. This gap prevented paleontologists from determining how exactly hagfish were related to other vertebrates. The Lebanese fossil was discovered due to a unique defense mechanism that is still found in modern hagfish.

Hagfish have the ability to turn the water around them into slime, which clogs the gills of nearby predators. This occurs because of tightly coiled keratin packets in the hagfish’s mucus that expand when they come in contact with water. Keratin was the key to finding the Tethymyxine tapirostrum.

The paleontologists used a technique called synchrotron scanning. This process allowed them to identify chemical traces of soft tissue left behind in the limestone when the hagfish ancestor fossilized.

By scanning for keratin, scientists were able to confirm that this fossil was an early form of hagfish and that their distinctive defense mechanism evolved before or during the Cretaceous period, millions of years ago.

“There are things that we know must exist but are elusive—an authentic sushi restaurant, the incorruptible Mayor of Chicago, the World Series-contending White Sox team, Dark Matter… Hagfish fossils kind of fall into that category for paleontologists,” Dr. Tetsuto Miyashita wrote in an e-mail to The Maroon.

“We know hagfish represent an ancient lineage so one would expect fossils. There is no hard part to their body, however, so it is very difficult to get it preserved into a fossil.”

With those results, Miyashita concluded that the hagfish and the lamprey, a relative of the hagfish, are part of the vertebrate family tree, but their rudimentary vertebral structure makes them an outlier among other vertebrates.

“What we thought was ancestral in vertebrates represents a highly derived state,” Miyashita explained. “For example, hagfish don’t have bones, so the earliest vertebrate was also considered boneless. But our paper suggests that the earliest vertebrate had a bony skeleton. The bony skeleton was later lost in the hagfish lineage.”

The research conducted in this study answered a question paleontologists have had for a long time. With the delineation of evolutionary lineages constantly in flux, many were unsure where the hagfish belonged. Miyashita’s work shows that hagfish are indeed vertebrates, and that their underdeveloped vertebrae may actually be specialized rather than primitive.