Fossilised slime attack from nightmarish fish helps solve big mystery

22 Jan 2019

A hagfish protruding from a sponge. Image: NOAA Okeanos Explorer Programme

The fossilised remnants of a hagfish, famous for its terrifying appearance, have been located, solving a puzzling evolutionary mystery.

It might not come as a surprise, given the name, that the hagfish is a marine creature you wouldn’t want to come across. Without eyes, jaws or teeth, the eel-like creature uses a spiky tongue-like apparatus to rasp flesh off dead fish and whales at the bottom of the ocean. When threatened, they disperse a thick cloud of slime capable of clogging the gills of any would-be predators.

The evolution of the hagfish has always puzzled palaeontologists, until the recent discovery published to the Proceedings of the National Academy of Sciences by a team from the University of Chicago Medical Center. Initially, the biggest question was how these ancient, jawless fish branched off the evolutionary tree from the lineage that gave rise to modern-day jawed vertebrates, including bony fish and humans.

The breakthrough came following the discovery of a 100m-year-old hagfish fossil in a slab of Cretaceous-period limestone from Lebanon. The fossil, named Tethymyxine tapirostrum, is 12in long and shows that hagfish are more closely related to blood-sucking lampreys than other fish.

Slab of brown limestone with the fossilised hagfish within it.

Tethymyxine tapirostrum, a 100m-year-old, 12in fish embedded in a slab of Cretaceous-period limestone from Lebanon. It is believed to be the first detailed fossil of a hagfish. Image: Tetsuto Miyashita/University of Chicago

Changes understanding of evolutionary history

The research shows that both hagfish and lampreys evolved their strange feeding mechanism after branching off from other vertebrate species approximately 500m years ago. What helped the researchers identify the fossil was the remnants of a slime attack it used prior to its death; otherwise, its soft tissue makes it almost impossible to find preserved.

Using advanced imaging technology, the team was able to pick up trace amounts of keratin, the same material that makes up our fingernails. As it turns out, keratin is also key to making the hagfish slime such a powerful deterrent.

Hagfish have a series of glands along their bodies that produce tiny packets of tightly coiled keratin fibres, lubricated by mucus-y goo. When these packets hit seawater, the fibres explode and trap the water within, turning everything into shark-choking slop.

More than 100 concentrations of keratin were found around the fossilised hagfish, suggesting this slime defence evolved in order to fight predators such as plesiosaurs and ichthyosaurs, which we no longer see today.

“We now have a fossil that can push back the origin of the hagfish-like body plan by hundreds of millions of years,” said Tetsuto Miyashita, who led the research. “Now, the next question is how this changes our view of the relationships between all these early fish lineages.”

Colm Gorey was a senior journalist with Silicon Republic