Armored Fish Evolved Two Different Ways to Crush Hard-Shelled Prey 385 Million Years Ago

Long before dinosaurs existed, armored fish called placoderms — the first vertebrates to evolve jaws and teeth, more than 400 million years ago — developed crushing bites to survive in ancient oceans. Researchers at Flinders University in Australia studied fossils from a 385-million-year-old reef in what is now northern Western Australia and found these early jawed fish evolved two distinct ways of biting armored prey.

The researchers, whose first author was Dr. Rex Mitchell, used a new combination of finite element analysis — a computer-based engineering technique — and three-dimensional digital bite simulations to reconstruct how eight placoderm species fed. The study, published in the journal Scientific Reports, modeled the biting forces supported by fossil jaw bones and compared them with the complexity of each species' biting surfaces.

Smaller placoderm species relied on broad, flat crushing plates to pulverize whole prey, while larger species evolved weapon-like teeth arranged along a raised bony crest — a structure resembling medieval armor-piercing weapons such as war hammers and poleaxes — to pierce and break apart shelled prey too large to swallow whole. Surprisingly, both the smallest and the largest species had the strongest jaws for hard bites despite using completely different biting tools, said Dr. Alice Clement, an ARC Future Fellow at Flinders University, and Ph.D. student Austin Fitzpatrick.

The researchers suggest the difference comes down to predator-to-prey size: smaller armored prey could be swallowed whole and crushed between flat plates, while larger prey first had to be broken into pieces, requiring dental structures capable of piercing armor before crushing it. Unlike humans, placoderms lacked a single lower jaw bone; their jaws instead consisted of paired bony plates supported by cartilage.

Flinders University emeritus professor John Long, a co-author who has worked at the Western Australian fossil site for 40 years, said placoderms have been directly linked to human evolution since 2013, as the start of the line leading from fishes to humans.