The placoderms in question lived around 385 million years ago during the Devonian Period, often called the Age of Fishes, in the rich marine ecosystems of the famous Gogo Formation in Western Australia. This world-renowned fossil site has been the focus of decades of research, including long-running collaborations with the local Gooniyandi and Gogo community, and has yielded some of the most exquisitely preserved three-dimensional fish fossils ever discovered. It was here that these armoured predators hunted other armoured creatures on an exotic ancient reef, and it is here that the fossil evidence for their feeding strategies has been locked away in stone, waiting for modern technology to unlock it.

Dr Alice Clement, an ARC Future Fellow at the Flinders Palaeontology Lab and a co-author of the study, explains that placoderms present an extraordinary natural experiment in the early evolution of biting. Placoderms experimented with an extraordinary range of jaw shapes and biting parts during the early evolution of vertebrates, she notes, providing a rare opportunity to understand how some of the first jaws became specialised for different diets. Unlike most animals alive today, including humans, placoderms did not possess a single lower jaw bone. Instead, their jaws were built from paired bony plates supported by cartilage, with biting surfaces that ranged from broad, flat crushing plates to sharp slicing edges armed with tooth-like structures. This anatomical diversity makes them ideal subjects for investigating how jaws first became adapted to different kinds of food.

To probe that diversity, the research team employed a technique borrowed from engineering known as finite element analysis. First author Dr Rex Mitchell, of the College of Science and Engineering at Flinders University, together with colleagues, created digital three-dimensional models of the fossil jaw bones and then performed computer-based bite simulations on them. These simulations measure how well each jaw structure could withstand and support the forces generated during biting, effectively stress-testing extinct animals in silico. The team then compared the mechanical performance of each jaw with the anatomical complexity of its biting surface, looking for patterns that might connect jaw shape to diet and feeding behaviour across the eight species they examined.

Conventional wisdom in biomechanics holds that animals feeding on hard foods, such as shells and bone, generally evolve stronger jaws with broader, flatter crushing surfaces, much like the nutcracker jaws of modern hyenas or the durophagous dentitions of many rays and wrasses. That is not exactly what the analysis revealed. Rather than finding a simple, predictable relationship between jaw strength and surface shape, the researchers discovered something unexpected: both the largest and the smallest placoderms in the study 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 carried highly complex, elevated dental surfaces that bore little resemblance to their diminutive relatives.

It was an interesting surprise, says PhD student and co-author Austin Fitzpatrick. Both the smallest and largest animals had evolved strong jaws, he explains, but they had solved the problem of processing harder foods in completely different ways. The key to this paradox, the researchers suggest, lies in the relationship between predator and prey body size when the prey in question is wrapped in tough exterior armour. A small placoderm confronting a small armoured prey item did not need to break it apart at all. The prey could simply be engulfed whole and then pulverised between broad, flat biting plates, much as some modern fish swallow and crush small shelled invertebrates. Strength was essential, but anatomical complexity was not.

Larger prey presented an entirely different challenge. An armoured animal too big to fit inside a predator’s mouth first had to be broken into manageable pieces before it could be eaten. That requirement demanded more elaborate dental architecture, capable of first piercing through shell or armour before crushing the remains. The largest species in the study possessed teeth arranged along a raised bony crest, forming a structure that the researchers describe as strikingly similar to the heads of medieval armour-piercing weapons such as war hammers and poleaxes. This fearsome configuration suggests the fish used its jaws to puncture the protective coverings of its prey before breaking them apart, functioning less like a nutcracker and more like a can opener followed by a hammer.

The broader significance of the finding is that hard-object feeding among Earth’s earliest jawed vertebrates was not achieved through a single evolutionary solution. Evolution, in other words, produced a diversity of jaw designs that allowed different placoderm species to exploit different prey within the same ancient reef ecosystem, a pattern ecologists call niche separation. Two species could both be powerful biters specialised for hard-shelled food, yet occupy genuinely different ecological roles depending on what they could fit in their mouths and how they had to dismantle it. This paints a picture of the Devonian reef as a complex, ecologically structured environment in which early vertebrates were already carving out specialised feeding niches hundreds of millions of years before the first tetrapods crawled onto land.

The study also reinforces the central place of placoderms in the story of human evolution. Flinders Emeritus Professor John Long, a co-author who has worked at the Western Australian fossil site for 40 years and found some of the specimens used in this study, emphasises that since 2013 placoderms have been directly linked to our own lineage as the starting point of the line leading from fishes to humans. Understanding placoderms, he argues, is now vital to revealing the origins of the human body plan. Their jaws, in particular, represent the evolutionary foundation upon which all later vertebrate mouths, from shark snouts to human faces, were ultimately built, making every new insight into how these structures functioned a contribution to a deeply personal chapter of natural history.

Technically, the study demonstrates the growing power of combining finite element analysis with comparative three-dimensional morphology to answer ecological questions that fossils alone cannot resolve. By measuring jaw strength numerically and then mapping it against surface complexity, the team could infer not only what these extinct fish ate but also how large their prey must have been relative to their own bodies, turning bite mechanics into a proxy for ancient food webs. The work, supported by the Australian Research Council through Discovery Projects funding, contributes to a growing picture of niche separation and ecological specialisation in the ancient Devonian reef. It shows that within a few tens of millions of years of jaws first appearing, vertebrates had already diversified into an impressive array of feeding specialists, from whole-swallowing crushers to armour-piercing giants, foreshadowing the extraordinary ecological breadth of jawed vertebrates that continues to this day.

Subject of Research: Feeding mechanics and jaw evolution in Devonian placoderms from the Gogo Formation, Western Australia

Article Title: Jaws tell tales: How ancient armoured fish munched prey whole

Article References: Jaws tell tales: How ancient armoured fish munched prey whole. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: placoderms, Devonian, Gogo Formation, jaw evolution, finite element analysis, hard-object feeding, palaeontology, Flinders University, vertebrate evolution, fossil fish, predator-prey relationships, ancient reefs

Lobe-finned fishes, a lineage that today counts only eight extant species including lungfish and coelacanths, underwent an explosive diversification of jaw morphologies and functions during the Devonian period—approximately 359 to 423 million years ago. This period, often dubbed the “Age of Fishes,” was pivotal in vertebrate history, marked by dynamic evolutionary experimentation. The research team employed high-resolution 3D models derived from CT scans of fossil specimens, meticulously reconstructing the jaw mechanics of 86 fish species spanning Silurian to Devonian periods. Their comprehensive analysis disclosed that lobe-finned fishes evolved jaw structures with markedly higher rates of change and functional innovation than their contemporaries, the ray-finned fishes.

Ray-finned fishes, today encompassing over 33,000 species and representing the most speciose vertebrate group, exhibited considerably slower evolutionary rates in jaw development during this era. This discovery is paradoxical given the vastly greater diversity and ecological dominance of ray-finned fishes in the present day. The coelacanth, a notable lobe-finned fish, famously rediscovered in 1938 after being considered extinct, underscores the group’s enigmatic legacy. Although modern lobe-finned fishes appear evolutionarily stagnant with limited jaw variation, the fossil record reveals an ancient past marked by rapid morphological experimentation and adaptation.

The lead author of the study, postdoctoral researcher Emily Troyer, emphasized the transformative insights afforded by integrating fossil data with cutting-edge imaging techniques. “Without the fossil record, we would have no idea of this inverted role reversal,” Troyer noted. The ability to peer back hundreds of millions of years enabled the researchers to challenge preconceived notions concerning evolutionary dynamics of early vertebrates. It also highlights the critical importance of paleontological data in understanding how major evolutionary innovations unfold through deep time.

Central to their investigation was the concept of mechanical advantage in jaw function—a biomechanical metric describing how effectively a jaw converts muscle force into bite force. By mapping mechanical advantage across species, the team could infer the functional consequences of observed morphological changes. Lobe-finned fishes developed robust, heavily muscled jaws during the early Devonian, an adaptation likely correlated with feeding on hard-shelled prey such as early clams and crustaceans. This suggests that ecological pressures related to diet played a crucial role in driving jaw diversification.

Digital reconstructions allowed detailed quantification of jaw shape, size, and leverage, revealing an adaptive radiation characterized by rapid morphological shifts. Adaptive radiation describes a process where a lineage diversifies rapidly into a range of different forms in response to ecological opportunities or innovations. The lungfish and coelacanth lineages, therefore, represent an ancient instance of this evolutionary principle, manifesting through novel feeding strategies embodied in jaw morphology and mechanics. These evolutionary adaptations were tightly linked with Devonian ecosystems, which presented new niches and resources.

Co-first author Rafael Rivero-Vega contributed significantly to the study by compiling CT scan data for nearly every complete fossil jaw of lobe-finned fishes available in museum collections. His work involved intricate 3D modeling and mapping of jaw characteristics to test hypotheses surrounding evolutionary tempo and mode. Rivero-Vega highlighted how each fish group encountered unique evolutionary pressures, resulting in distinct patterns of jaw diversification and stasis. Some evolved rapidly before stabilizing upon reaching functional ecological niches, while others displayed more gradual morphological changes aligned with terrestrial transitions.

This research frames evolutionary innovation as a variable and context-dependent process, with different vertebrate lineages exploring morphological and functional possibilities at their own pace. The Devonian jaw innovations in lobe-finned fishes predate the rise of tetrapods and the well-known dinosaur clades by hundreds of millions of years, demonstrating how foundational these early adaptations were to vertebrate evolution. Additionally, the study provides a nuanced understanding of how the interplay between form, function, and environment shapes evolutionary pathways.

The implications extend beyond paleontology, informing developmental biology and ecology by illustrating how morphological traits can be influenced by both biomechanical constraints and ecological opportunity. The use of advanced imaging technologies like CT scanning and 3D biomechanical modeling serves as a blueprint for future evolutionary investigations, enabling scientists to derive functional insights from fossilized remains that were previously unattainable. These methodological innovations breathe new life into the study of ancient life, bridging gaps between form and function across geologic epochs.

In sum, the discovery of a shifted evolutionary tempo between lobe-finned and ray-finned fishes during the Devonian challenges conventional narratives about vertebrate history. Rather than a straightforward trajectory toward the modern dominance of ray-finned fishes, the fossil record reveals a complex story of innovation, experimentation, and adaptation. This study not only underscores the richness of this evolutionary tapestry but also invites a reconsideration of how evolutionary potential is expressed unevenly across diverse lineages and time periods.

Subject of Research: Animals
Article Title: Macroevolutionary role reversals in the earliest radiation of bony fishes
News Publication Date: 1-Sep-2025
Web References: http://dx.doi.org/10.1016/j.cub.2025.08.008
Image Credits: E.M. Troyer/University of Michigan
Keywords: Life sciences, Developmental biology, Ecology, Evolutionary biology