If you’re reading this sentence, you might have a fish to thank. The simple act of opening your mouth to speak, eat, or even breathe carries with it an ancient legacy: jaws. More than 400 million years ago, the first fish evolved jaws, forever changing the story of life on Earth.
Jaws were not just for eating. They became tools for defense, weapons of survival, and even cradles of care—some fish still carry eggs or young inside their mouths. This innovation reshaped ecosystems, sparked evolutionary explosions, and, ultimately, paved the way for vertebrates like us to thrive. Without jaws, the path from fish to humans might never have been possible.
A Revolution Beneath the Waves
Recently, scientists at the University of Michigan uncovered a surprising twist in this ancient story. Their research revealed that a now-rare group of fish—the lobe-finned fishes—once dominated evolution with their rapidly changing jaws. Between 359 and 423 million years ago, these fishes experienced an extraordinary burst of diversity. Their jaws evolved in unexpected shapes and functions, unlocking new feeding strategies that allowed them to conquer ecological niches with remarkable speed.
This discovery is astonishing because today, lobe-finned fishes are a ghost of their former selves. Only eight living species remain, including the enigmatic coelacanth and lungfish. In stark contrast, their evolutionary rivals—the ray-finned fishes—went on to flourish spectacularly. Today, with more than 33,000 species, ray-finned fishes include everything from shimmering goldfish to fearsome barracudas.
What makes this story so compelling is not only the evolutionary drama, but also the reminder that history is rarely what we expect. The champions of yesterday can fade into obscurity, while the underdogs rise to dominance.
Living Fossils and Lost Worlds
The coelacanth is perhaps the most famous of the surviving lobe-finned fishes. For millions of years, it was believed to have gone extinct, remembered only in fossils. But in 1938, off the coast of South Africa, a living coelacanth was caught and recognized by Marjorie Courtenay-Latimer, a museum curator whose discovery stunned the world. This “living fossil,” with its lobed fins and ancient features, became a symbol of survival against all odds.
Yet the new University of Michigan study reveals that the coelacanth’s ancestors were not evolutionary relics. They were innovators, experimenting with jaw shapes that gave them incredible feeding abilities. These ancient lobe-fins weren’t clinging to survival; they were leading the charge of evolution itself.
Reading the Fossil Record
To uncover this hidden history, researchers turned to the fossil record of the Silurian and Devonian periods—eras when fish ruled the seas, long before the first forests took root on land. Using CT scan technology, the team created 3D models of 86 fossilized jaws, each belonging to a different species of early fish.
They weren’t just looking at shapes—they were decoding function. By measuring the “mechanical advantage” of jaws, they could estimate bite force and feeding strategies. A higher mechanical advantage meant stronger bites, perfect for crushing hard-shelled prey like clams and early crustaceans.
The results were striking: lungfish, in particular, showed a surge of jaw innovation. Their jaws became massive, heavily muscled, and perfectly adapted for cracking tough food. These changes suggest that evolving ecosystems were pressuring fishes to exploit new diets, fueling an evolutionary arms race.
The Age of Fishes
The Devonian period, often called “The Age of Fishes,” was a time of dazzling experimentation in vertebrate evolution. Some species developed crushing jaws. Others specialized in speed, precision, or suction feeding. Each adaptation represented not just survival, but a step toward filling new ecological roles.
Rafael Rivero-Vega, one of the study’s authors, described it as a series of unique evolutionary “moments.” Some fishes diversified rapidly, only to settle into stable forms once they found their niche. Others remained conservative in shape until opportunities pushed them to change. These patterns mirror the broader story of life on Earth: bursts of creativity followed by periods of calm.
Why Jaws Mattered
Jaws were more than just a feeding tool. They were a gateway innovation, unlocking new ecological possibilities. With stronger, more versatile jaws, fishes could tackle harder prey, defend themselves more effectively, and explore new food sources. This adaptability helped vertebrates push boundaries, eventually leading some to crawl onto land.
When we chew, smile, or speak, we are living reminders of that ancient leap. The very structure of our faces is shaped by an evolutionary gamble made hundreds of millions of years ago.
Lessons from Deep Time
The study highlights something crucial: without fossils, this story would have been lost. If scientists had only studied living species, they might have concluded that lobe-finned fishes were evolutionary dead-ends. Instead, the fossil record reveals them as once-vibrant innovators.
Emily Troyer, lead author of the study, put it simply: “When you’re looking at evolution, you can learn so much from looking at the past. Without the fossil record, we would have no idea of this inverted role reversal.”
This is the magic of paleontology. Fossils are not just bones and rocks—they are time machines. They show us not only what lived, but how life struggled, adapted, and flourished.
Echoes of the Ancient Seas
Today, when we look at a coelacanth gliding silently in the deep ocean or a lungfish surfacing to gulp air, we are witnessing echoes of an ancient age. They are survivors of a time when their ancestors ruled the seas with jaws that reshaped evolution.
Their story is humbling. It reminds us that dominance is fleeting, that innovation is often temporary, and that survival sometimes depends more on endurance than brilliance. It also reminds us that the roots of our own humanity—our jaws, our ability to bite, chew, and speak—are gifts passed down from these ancient pioneers.
Why This Story Matters to Us
The tale of lobe-finned fishes is not just about dusty fossils or long-dead animals. It is about the power of innovation, the unpredictability of survival, and the importance of memory. By studying these forgotten creatures, we learn not only about the history of life, but about our own story as part of it.
Science tells us that evolution is not a straight line. It is a branching tree, full of experiments, failures, and astonishing successes. The lobe-finned fishes remind us that even the mightiest branches can shrink, while others burst into bloom.
When you bite into your next meal or laugh with your friends, pause for a moment. The jaws that make it possible are more than just bones—they are the legacy of ancient fish who, hundreds of millions of years ago, changed the world forever.
More information: Emily M. Troyer et al, Macroevolutionary role reversals in the earliest radiation of bony fishes, Current Biology (2025). DOI: 10.1016/j.cub.2025.08.008
