Long before dinosaurs roamed the Earth, a different kind of predator ruled the ancient oceans — and new research shows these armored hunters figured out two completely different ways to crush their dinner.
Scientists at Flinders University in Australia used a clever new technique to study the jaws of placoderms, the very first vertebrates to evolve jaws and teeth more than 400 million years ago. These armored fish once swam over an exotic reef that covered what is now northern Western Australia, in a famous fossil site called the Gogo Formation.
The team was surprised to discover that these early jawed fish developed two distinct ways of biting armored prey. The smaller species relied on broad, flat crushing plates to pulverize whole animals. The larger species, meanwhile, grew weapon-like teeth designed to pierce and break apart shelled prey that were simply too big to swallow whole.
"We know that animals feeding on hard foods usually evolve stronger jaws and broader, flatter crushing surfaces, but that's not exactly what we found in this analysis," said Dr. Alice Clement, an ARC Future Fellow and one of the researchers.
To figure out how eight different species fed in the oceans 385 million years ago, the researchers built 3D models of fossil jaw bones and ran digital bite simulations. Dr. Rex Mitchell, the study's first author published in Scientific Reports, wanted to measure how well each jaw supported biting forces.
Here's the unexpected twist: both the smallest and largest placoderms had the strongest jaws, but they arrived at that strength in totally different ways. The smallest species had broad, almost featureless crushing plates. The largest featured highly complex, elevated dental surfaces.
"It was an interesting surprise," said Ph.D. student and co-author Austin Fitzpatrick. "Both the smallest and largest animals had evolved strong jaws, but they'd solved the problem of processing harder foods in completely different ways."
The secret, the researchers suggest, is all about size. Small armored prey could simply be swallowed whole and crushed between flat plates. But larger prey — animals too big to gulp down — had to be broken into pieces first. That required teeth shaped for piercing armor before crushing it.
The largest species had teeth arranged along a raised bony crest, forming something strikingly similar to the heads of medieval armor-piercing weapons like war hammers and poleaxes. These fish would puncture their prey's shell, then break it into manageable chunks.
"Placoderms experimented with an extraordinary range of jaw shapes and biting parts during the early evolution of vertebrates," Clement said. "They provide a rare opportunity to understand how some of the first jaws became specialized for different diets."
Unlike humans, placoderms didn't have a single lower jaw bone. Instead, their jaws were made of paired bony plates held together by cartilage, with surfaces ranging from broad crushing plates to sharp slicing edges with tooth-like structures.
The findings show that hard-object feeding among Earth's earliest jawed vertebrates wasn't the result of one evolutionary solution. Instead, evolution produced a whole menu of jaw designs, letting placoderms exploit different prey across the ancient reef. Co-author Professor John Long has been working at the Gogo Formation for 40 years and found some of the very specimens used in this study.