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 armoured 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 fishes evolved two different ways of biting other armoured 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 specialised for different diets."
While the smaller species examined relied on broad, flat crushing plates to pulverise prey whole, the larger species evolved weapon-like teeth that pierced and broke apart shelled and armoured 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," says Dr Clement, from the Flinders Palaeontology Lab.
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 of 385 million years ago.
Dr 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," says Dr Mitchell, from the College of Science and Engineering at Flinders University.
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 PhD 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 onto armoured prey with tough exterior shells.
Smaller armoured prey could simply be engulfed in the mouth whole and crushed between broad, flat biting plates. Larger prey, however, first had to be broken into smaller pieces before they could be eaten. This required more complex dental structures capable of piercing armour before crushing it.
The largest species in the study possessed teeth arranged along a raised bony crest, forming a structure strikingly similar to the heads of medieval armour-piercing weapons such as war hammers and poleaxes. This suggests the fish used its jaws to puncture the shells or armour of prey before breaking them into manageable pieces.
The findings show that hard-object feeding among Earth's earliest jawed vertebrates was not achieved through a single evolutionary solution. Instead, evolution produced a diversity of jaw designs that allowed placoderms to exploit different prey within the ancient reef ecosystem.
Flinders Emeritus Professor John Long , another co-author of the latest study, has been working at the WA fossil site for the past 40 years and found some of the specimens used in this study.
The world-famous Gogo Formation in WA has been the focus of long-running research, including collaborations with the local Gooniyandi and Gogo community.
"Since 2013, placoderms have been directly linked to our evolution, as the start of the line leading from fishes to humans. Understanding placoderms is now vital to revealing the origins of the human body plan," adds Professor Long. "Our work contributes to a growing picture of niche separation and ecological specialisation in the ancient Devonian reef during the so-called 'Age of Fishes' which is now acknowledged as the long line leading from fishes to humans."
The article, ' Hard-object feeding adaptations infer relative predator-prey size relationships in Devonian placoderms' (2026) by D Rex Mitchell, Kate Trinajstic (Curtin University), John A Long, Austin N Fitzpatrick, Joshua Bland and Alice M Clement has been published in Scientific Reports. DOI: 10.1038/s41598-026-57261-3.
Acknowledgements: This work was supported by the Australian Research Council Discovery Projects funding (DP 220100825 and DP 240102156). Thanks to the Gooniyandi and Gogo community for access to specimens.
photos supplied with captions available: https://drive.google.com/drive/folders/1gDVEuQX86djDXVkKGKrRqD-i5lMI603i?usp=sharing
