How a 310-Million-Year-Old Fish Shows Evolution’s Talent for Repurposing and Reinventing the Jaw

By Stephanie Godward, Communications and Marketing Director, College of Arts & Sciences  

Assistant Professor of Biology Matt Kolmann’s recent collaborative research on ancient fish reveals an aspect of evolution in which existing jaw structures were repurposed as fish evolved to find new ways to capture and eat prey. 

“The cool thing is that over 300 million years, fishes keep evolving teeth on their tongues to crush stuff,” Kolmann said. “It’s neat seeing how these skeletal structures evolve, and how they have recurring uses throughout time.” 

Co-author of the paper, “Tongue-bite apparatus highlights functional innovation in a 310-million-year-old ray-finned fish,” published in Biology Letters, Kolmann and his collaborators explore the earliest known example of a fish with extra teeth deep inside its mouth – a fossilized ray-finned fish that evolved a unique way of devouring prey. 

“We describe the earliest known example of a fish with a second set of jaws - specifically one that has teeth on its ‘tongue,’ which it used to crush stuff by mashing food between the tongue and palate or roof of the mouth,” Kolmann said.  

The long and short of it: all animals with backbones, including humans, have jaws. Jaws evolved from the gill skeleton. Fishes have kept going with this trend and have added secondary jaws behind their first set (like the "famous" eel example). 

“The cool thing about this – and we don’t think about it much – is that when we eat, there are stages. The first stage is that you have to capture food. Cats grab things with their claws, birds feed with their feet, and we kind of grab food and stuff it into our mouths. And so, our mouths, our jaws, are there to process the food,” Kolmann said. “But fishes don’t have hands. So, they suck food into their mouths and then they have to process and break down that food. What's so cool about this ‘tongue bite’ is that they are actually using the tongue to process and to chew the food, and not the jaws.” 

This research has a broader context and gives us insight into what early jawed vertebrates – any living thing with a backbone - were doing throughout evolution, Kolmann said. He went on to say vertebrates really explode on the scene when they evolve with jaws, which evolved from gill arches.  

“What’s really cool about this tongue bite is it’s a good story about these early fishes experimenting with different ways of accessing new foods,” Kolmann said. “It’s kind of trial and error. Some try and don’t go very far, and some succeed and keep going.” 

Human jaws and the fish "tongue bite” are built and adapted from the same components. They are part of the gill skeleton and there are lots of weird things that fishes do with their gill skeletons, he went on to explain. 

“And I think it’s a really cool example of how evolution repurposes parts that are already there to fill new like functions,” Kolmann said. “Eventually, some of our gill skeletons go on to form inner ear bones (in mammals). Evolution doesn’t waste anything. It always just finds a new role for it.”