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

Sharks are continuously shedding dermal denticles throughout their lives. These microscopic structures cover the animals’ bodies and perform several functions, including reducing drag as sharks swim, protecting the skin, and influencing how water moves across the body. Unlike ordinary fish scales, dermal denticles are made from a hard, tooth-like material and often possess distinctive shapes that vary among species and ecological types. Once shed, they sink into reef sediments, where their mineralized structure can persist for millions of years. By counting denticles in sediment layers whose ages can be determined, researchers can estimate how frequently sharks occupied the surrounding reef environment at different points in the past. The method functions as a biological archive, preserving evidence of shark communities from periods long before systematic fishing records existed.

The research team applied this approach to sediments deposited between approximately 7,000 and 3,000 years ago, a period that predates intensive industrial fishing, and compared those ancient layers with sediments deposited during the past century. Across 157 samples, the scientists recovered 3,497 denticles. The number of scales in each sample was adjusted using models that accounted for factors such as sediment age, sampling effort, and variation in deposition. This allowed the researchers to compare denticle accumulation rates rather than simply counting raw fragments. A higher accumulation rate indicates that more sharks were likely swimming over or near a reef, shedding denticles that eventually became incorporated into the seafloor. Because the approach captures the combined signal of many animals over time, it can reveal broad population baselines that are impossible to reconstruct from scattered historical observations.

The first striking contrast appeared during fieldwork. In Bocas del Toro on Panama’s Caribbean coast, the team found roughly 50 shark denticles in 10 kilograms of reef sediment. A much smaller sample from a Pacific reef contained about 200 denticles in only one kilogram of sediment. As more material was processed and the data were analyzed, the initial impression became statistically robust. Before humans began fishing at large scales, reefs in the Gulf of Panama supported roughly 20 times more sharks than comparable Caribbean reefs. Over the following centuries, the two coastlines diverged even more. Denticle accumulation on the Caribbean side declined by about 75 percent, while accumulation on the Pacific side remained statistically similar to its prehistoric baseline when averaged across the last hundred years. Today, Pacific reef sediments yield approximately 100 times more denticles than Caribbean sediments.

That result is especially surprising because Panama’s Pacific coast has experienced much heavier fishing pressure. More than 98 percent of the country’s fishing activity occurs there, meaning the Pacific reefs have faced substantially greater direct human exploitation than their Caribbean counterparts. The explanation, according to the researchers, lies in the physical and chemical differences between the two marine environments. The Gulf of Panama is strongly influenced by seasonal upwelling, a process in which winds and ocean circulation bring cold, nutrient-rich water from depth toward the surface. These nutrients stimulate plankton growth and support a productive food web capable of sustaining large predator populations, including sharks. The Caribbean coast of Panama is comparatively nutrient-poor. Its clear tropical waters may resemble the classic image of a coral reef, but lower external productivity means that more of the ecosystem’s energy is stored within reef organisms themselves, leaving shark populations smaller and potentially more vulnerable to fishing.

The ecological distinction changes how scientists should interpret reef recovery. Conservation programs often use the healthiest nearby reef as a reference point, assuming that neighboring ecosystems should support similar numbers of predators or that fishing has affected them in broadly comparable ways. In Panama, that assumption could produce a severe error. If Pacific shark abundance were used as the recovery target for Caribbean reefs, managers might establish goals that are unrealistic for a naturally less productive ecosystem. Conversely, if the lower Caribbean baseline were applied to the Pacific, managers could underestimate the number of sharks that a productive upwelling system can support. The study indicates that ocean productivity must be considered alongside fishing history, habitat quality, climate, and species composition when setting population targets. A reef cannot be evaluated accurately without accounting for the energy available to its food web.

The fossil record does not mean that Pacific sharks are safe. The comparison with ancient sediments may conceal more recent changes because the modern reference samples span roughly a century. Targeted shark fishing in the Gulf of Panama accelerated during the 1980s, so a steep decline in recent decades could be diluted when combined with sediments deposited earlier in the twentieth century. Other research has already shown that shark populations in Pacific Panama are under pressure from intensified fishing. The region may also be entering a period of ecological change: the seasonal upwelling that supplies the Gulf with cold, nutrient-rich water failed for the first time on record last year. If overfishing reduces shark populations while climate-driven changes weaken the productivity that supports them, the Pacific coast could be pushed toward a condition not experienced for thousands of years. Its apparent resilience may therefore represent a capacity for recovery rather than proof that recovery is unnecessary.

Developing the denticle method required more than a decade of work. The project began with the unconventional idea that reef sediments might contain enough shark scales to reconstruct ancient predator communities. Researchers first had to determine which denticles could be reliably identified, how to extract them from complex carbonate sediments, and how differences in denticle shape reflected shark species or ecological lifestyles. False-color scanning electron microscopy helped reveal the fine architecture of the scales, including ridges, crowns, and other microscopic features that can vary among sharks. These characteristics allow researchers to examine not only how many sharks were present but also whether the composition of the shark community changed through time. The work began when lead author Erin Dillon was an intern at STRI in 2014, continued through her doctoral research at the University of California, Santa Barbara, and later developed during her postdoctoral fellowship in Panama.

The study’s most powerful implication is that the ocean floor may preserve a record of ecological loss that conventional monitoring cannot see. Sharks are among the most difficult marine predators to survey because they move across large areas, occur at low densities, and can disappear from heavily fished ecosystems before scientists establish reliable population baselines. Dermal denticles provide a new source of evidence, linking the physical history of sediments with the biological history of predator communities. In Panama, they show that geography alone does not determine shark abundance: the productivity of the surrounding ocean can create radically different natural baselines on nearby reefs. As scientists extend the technique to other regions, microscopic “shark dandruff” could help reveal how many predators ecosystems once supported, distinguish natural differences from human-driven declines, and identify recovery targets grounded in the ecology of each reef rather than in assumptions based on the nearest surviving population.

Subject of Research: Shark abundance baselines, fossil dermal denticles, coral reef ecology, ocean productivity, and conservation targets.

Article Title: Fossil denticles reveal how ocean productivity shapes shark baselines and recovery potential.

Web References: https://doi.org/10.1126/science.aec2144

References: Dillon, E.M., McCauley, D.J., Gonzalez, M., Connolly, S.R., de Gracia, B., Cybulski, J.D., Norris, R.D., Gómez, M.M., Garcia-Pérez, I., Leonard, N.D., Zhao, J., García-Méndez, K., O’Dea, A. 2026. “Fossil denticles reveal how ocean productivity shapes shark baselines and recovery potential.” Science.

Image Credits: Erin Dillon, Jorge Ceballos, Aaron O’Dea, and Ashley Diedenhofen.

Keywords: Sharks, shark denticles, shark dandruff, coral reefs, fossil sediments, dermal denticles, Panama, Gulf of Panama, Caribbean Sea, ocean productivity, seasonal upwelling, overfishing, marine conservation, reef ecosystems, Science.