Dunkleosteus looked like a brute, and it probably was one. It thrived during the Devonian Period (also known as the “Age of Fishes”), millions of years before the first dinosaur. This fearsome fish weighing over a ton was among the largest and most formidable animals of its time, earning its place as one of Earth’s first apex predators.

An ancient, fearsome predator

Dunkleosteus is an extinct fish that lived some 380 to 360 million years ago. Dunkleosteus wasn’t like the fish we know today. It belonged to a now-extinct group of armored fish called placoderms. It’s called a “placoderm” because its head and thorax was covered in armored plates. This was generally how fish were built in that time; placoderms were the dominant type of fish for 100 million years.

Out of them, Dunkleosteus was probably the most fearsome.

Sometimes measuring over 20 feet (6 meters) in length and weighing over a ton, Dunkleosteus combined sheer size with terrifying weaponry. Its most remarkable feature was its head—covered in thick, bony armor and housing powerful, scissor-like jaws. Unlike modern sharks, which use sharp teeth to slice their prey, Dunkleosteus used bony plates that acted like guillotine blades. These plates could close with incredible force, allowing them to crush almost anything in their path.

There were several Dunkleosteus species. The largest of them, D. terrelli, measured up to 10 meters (33 feet). They were probably slow, but very powerful swimmers; fear-inspiring predators that roamed the coastal areas feasting mostly on free-swimming creatures like arthropods and ammonites. Frequently, fossils of Dunkleosteus are found with boluses of fish bones which seems to indicate that they ate the prey whole, and then regurgitated the bones instead of digesting them.

Scientists estimate that Dunkleosteus’ bite force reached 8,000 pounds per square inch—stronger than that of modern crocodiles and some species of sharks. This enabled it to tackle a variety of prey, from armored fish to early sharks, cephalopods, and other marine creatures. Fossil evidence even suggests cannibalistic tendencies, with bite marks matching Dunkleosteus’ jaws found on the bones of its own kind.

Life in the Devonian

Dunkleosteus lived during the Devonian Period, a time of flourishing marine life. Coral reefs expanded, and jawed fishes diversified. Yet it was also a perilous time, with predators like Dunkleosteus shaping the evolution of marine organisms. Prey species evolved thicker armor or faster swimming techniques to survive, while predators adapted to breach these defenses.

The Devonian seas were teeming with diversity. From the ammonites with their coiled shells to other placoderms and primitive sharks, competition was fierce. The fact that Dunkleosteus was dominant during this competitive period shows just how fearsome of a predator it was.

Dunkleosteus was one of the last great placoderms before their extinction at the end of the Devonian. A mass extinction event, possibly linked to climate change and anoxia (oxygen depletion in oceans), wiped out many marine species, including Dunkleosteus. This extinction marked the end of placoderms but set the stage for the rise of other vertebrate groups, such as bony fish and sharks, which now dominate aquatic ecosystems.

How we know so much about it

Most of what we know about Dunkleosteus comes from fossilized skull plates and jaw fragments. Its cartilage skeleton, like that of modern sharks, is rarely fossilized, leaving much of its body structure to speculation. Paleontologists have reconstructed its probable shape using comparative anatomy and biomechanical modeling, envisioning a streamlined predator built for speed and power.

Numerous fossils have been found scattered across the globe, from North America to Morocco. This means that Dunkleosteus thrived in the incredible biodiversity of ancient marine ecosystems.

Modern technology has also brought Dunkleosteus out of textbooks and into the public eye. Museums use 3D printing to create life-sized models of this predator, and digital simulations allow scientists to explore its biomechanics.

Oh, and in case you’re wondering about the name, Dunkleosteus was named in 1956 to honor David Dunkle, then curator of Vertebrate Paleontology at the Cleveland Museum of Natural History. If you’re looking for some great fossils, the Cleveland museum has some of the best.