This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Long before dinosaurs appeared on Earth, fierce predatory fish developed crushing jaws and sharp teeth to survive and diversify in ancient oceans. Flinders University researchers have used a new combination of techniques to find out how these armored fish called placoderms—the first vertebrates to evolve jaws and teeth more than 400 million years ago—caught their prey on an exotic ancient reef that once covered what is now northern Western Australia.
The scientists were surprised to discover these early jawed fish evolved two different ways of biting other armored prey in the rich marine ecosystems of prehistoric Australia. "Placoderms experimented with an extraordinary range of jaw shapes and biting parts during the early evolution of vertebrates," says Dr. Alice Clement, an ARC Future Fellow.
"They provide a rare opportunity to understand how some of the first jaws became specialized for different diets." While the smaller species examined relied on broad, flat crushing plates to pulverize whole prey, the larger species evolved weapon-like teeth that pierced and broke apart shelled and armored prey that were too large to swallow. "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," Clement says. The researchers used a new finite element analysis technique, with computer-based simulations and three-dimensional analysis of their biting surfaces, to reconstruct how eight of these species fed in the oceans 385 million years ago.
Rex Mitchell, the first author of the study published in Scientific Reports, studies the relationship between diet and skull shape to explain ecology and evolution. "Unlike many animals around today, including humans, placoderms did not possess a single lower jaw bone. Instead, their jaws consisted of paired bony plates supported by cartilage, with surfaces ranging from broad crushing plates to sharp slicing edges with tooth-like structures," Mitchell says.
The researchers performed digital bite simulations on 3D models of the fossil jaw bones to measure how well they supported biting forces before comparing these results with the complexity of each species' biting surface. Rather than finding a simple relationship, they discovered that both the largest and smallest placoderms possessed the strongest jaws for handling hard bites, despite using completely different biting tools. The smallest species had broad, almost featureless crushing plates, while the largest species possessed highly complex, elevated dental surfaces.
"It was an interesting surprise," says 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 answer, the researchers suggest, lies in the relationship between predator and prey body size when it comes to biting armored prey with tough exterior shells. Smaller armored prey could simply be engulfed whole and crushed between broad, flat biting plates.
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