Discover the 30 Foot, Armored Sea Monster With a T-Rex Bite

3D illustration of Dunkleosteus ready to devour several fish at one time
© Catmando/

Written by Krishna Maxwell

Updated: April 27, 2023

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Many fearsome creatures have come and gone throughout the earth’s long history. The mass extinction of the biggest and fiercest allowed to rise of mammals, including humans. We now dominate the entire planet, but that might not have happened if we had to share the world with creatures like these.

Dunkleosteus, the strongest fish of its age, lived about 380 million years ago. It was the largest predator and one of the fiercest creatures ever in marine life. This sea monster had bony ridges instead of teeth, with two sets of fang-like protrusions that gave it the strongest bite force. However, the ridges changed to segments with time, allowing them to feed on the biggest fish, even sharks!

The armored sea monster (Dunkleosteus) belongs to an extinct genus of large-jawed fish, arthrodire placoderm. It consists of species like the D. belgicus, D. marsaisi, D. raveri, and D. terrelli, the largest. The species of Dunkleosteus varied in size, as some measured about 20 feet. This giant fish is named after a paleontologist, and its name means Dunkles Bone.

Here is more information about Dunkleosteus, its size, what it fed on, and where it lived. This fish was a sea monster with many predators but faced life challenges.

Description and Size

Dunkleosteus existed during the Late Devonian Period. It was named so in 1956 in honor of David Dunkle. Its skin was armored and tough, a reason it’s body survived many years after extinction.

The largest species of dunkleosteus, D. terrelli measured about 30 feet and weighed over one ton. However, some dunkleosteus species are as short as 3 feet. Some of the distinctive features of this giant fish are:

  • The fish had strong jaws that could chop up sharks and other marine creatures.
  • Its skull was made up of thick bony plates, which provided it extra protection from its predators.
  • It had strong jaws, with two lower jawbones that were as long as a man’s forearm.
  • The teeth were ridged, and two sets of fang-like teeth protruded near the front of the jawbone. These teeth later evolved into segments that were stronger to catch prey.
  • Its two-part bony, armored exterior made it a slow but powerful swimmer.
  • The D. terrelli had a shark-like body, with an anterior lobe on the tail.
3D rendering of dunkleosteus

Dunkleosteus had a two-part bony, armored exterior that made it a slow but powerful swimmer.

©Esteban De Armas/

What Did Dunkleosteus Eat?

Dunkleosteus lived in the shallow waters of seas and oceans, and it mostly fed on other marine animals. However, it was a carnivore with a strong body and a powerfully built and armored plate on its head resembling the shark. The strong jaw and body made it one of the fiercest sea creatures, and it could feed on fish and sharks.

The jaws opened at high speed, and the fish could make a powerful bite with more force than a crocodile and T-Rex. The fast movement of the jaws was due to the movable joints between the jaws and the muscles. The newly evolved segments could hold the prey easier, and the fish could bite through a bony plate of other big fish.

This sea monster also fed on smaller fish of its kind. However, the remains show that dunkleosteus might have suffered from indigestion because there were remains of indigested fish among its fossils.

Dunkleosteus Changes During Growth

During the study of the fossils, the research team compared the mouth sizes and types of jaws at different stages of life. As a result, they discovered changes, like the segment’s growth during adolescence and evolution in the jaw shape.

The research concluded a niche shift as the fish grew older. In addition, its feeding capabilities changed with changes in its body. For example, it fed on soft-bodied prey when it was young, hence the scissor-like jaws.

When it grew older, the jaw lengthened, and the fangs grew to their adult length. The jaws also became stronger and could crush anything, enabling the fish to attack bigger prey. The strong jaws and segments made it the strongest in the Devonian Ocean.

3D rendering of Dunkleosteus on white background

Adult Dunkleosteus had strong jaws that could crush anything, enabling them to attack bigger prey.



Dunkleosteus is a fish that lived in the shallow waters of seas and oceans with other placoderms and free-swimming fish. The blue whales and puffer fish are other marine creatures that live in a similar environment.

However, the adult D. terrelli lived in the deep parts of the oceans and seas while the adolescent lived in the shallow parts. Also, the D. terrelli was a fast-moving reptile, unlike dinosaurs that lived during its time.

The fossils of the dunkleosteus were discovered near North America, Poland, and Belgium. It was first discovered in 1873, but the paleontologists named it in honor of David Dunkle, the curator of vertebrate paleontology at Cleveland Museum in 1956.

Threats and Predators

Although this king of marine life posed a threat to the other aquatic animals, the creature was also threatened. As evolution continued, there was a rise of bony fishes and more sharks that posed competition to the slow-swimming dunkleosteus.

Besides posing a competition in swimming and getting most of the food in the ocean, the newly evolved sharks were also favored by the marine environment. However, dunkleosteus terrelli was their huge predator.

The D. terrelli was bigger with a strong jaw and armor-plated bones. Its jaws had the strongest biting force than the strongest alligators and could feed on any fish and sea creature, and it also fed on other dunkleosteus.

Discoveries and Fossils of the Dunkleosteus

The first fossils of dunkleosteus were discovered in 1867 in various U.S. states. However, the D. marsaisi fossils were found in Morocco and the D. amblodoratus in Canada. Texas, California, and Ohio are other states associated with this giant fish’s remains. History also says that there is a fossil site for dunkleosteus in Pennsylvania. However, the most famous specimen of this fish is from Cleveland Shale in Northern Ohio.

Today, you can find dunkleosteus remains in the Cleveland Museum of Natural history. The museum houses its strong skull and fearsome jaws, but no remains of its backbone and soft body tissues exist. Some of these remains were preserved from 1965 to 1967 after the Ohio Department of Transport excavated significant discovery of the marine fish.

The Cause of Dunkleosteus Extinction

Dunkleosteus started becoming extinct during the Devonian period, approximately 358-382 million years ago. During this time, over 70% of the fish were lost forever. There are different reasons for the disappearance of this fish, with some scientists attributing it to low oxygen levels in the sea, an asteroid hitting the states, and suffocation by debris. Here is a detailed explanation of these causes:

Low Oxygen Levels

Two significant events happened during the Devonian period: Kellwasser and Hangenberg. These were accompanied by ocean anoxia or low oxygen levels. This phenomenon was confirmed when paleontologists discovered a black shale, a layer that forms due to ocean anoxia.

The reduced amounts of oxygen led to the death of many animals and reptiles, including the dunkleosteus. In addition, the reef-builders, like corals, also died with trilobites and other creatures.

Volcanic Activities

Another reason for the extinction of dunkleosteus was volcanic activities. The eruption of mountains during the Devonian period contributed to less oxygen supply in the ocean, which was not a factor during the Permian extinction. Volcanoes may have also led to mercury poisoning.

Asteroid Strike

A colossal asteroid strike during the Devonian extinction led to the death of all dunkleosteus. This event caused a crate in the Gulf of Mexico. The asteroid strike was too strong, boiling part of the ocean and killing everything in the water.

The increased heat also killed most of the plankton, a significant food for the fish. Therefore, even the species not near the area stricken by the asteroid eventually died due to starvation.

Debris From the Asteroid

When the asteroid hit the ocean, there was a lot of movement in the sea. As a result, the fish and other marine life were covered by debris, preventing the air from flowing adequately, leading to suffocation. The debris also covered plankton and plants, leaving nothing to survive.

Similar Animals to Dunkleosteus

Other animals shared characteristics with the dunkleosteus. Some of them are:

  • Dinichthys: It is an extinct giant, marine arthrodire placoderm from the Late Devonian (Famennian stage), similar in shape, size, and ecological role to Dunkleosteus. At first, they were both grouped in the family Dinichthyidae. However, the Carr & Hlavin phylogenetic study in 2010 revealed that Dunkleosteus and Dinichthys belong to two separate clades.
  • Lamprey: It is thought to be the closest living relative to Dunkleosteus although they don’t seem to have much in common directly. However, these unique fish had a coat of armor surrounding their head and a portion of their thorax, which served as a type of “exoskeleton” for them.

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About the Author

Krishna is a lifelong animal owner and advocate. She owns and operates a small farm in upstate New York which she shares with three dogs, four donkeys, one mule, and a cat. She holds a Bachelors in Agricultural Technology and has extensive experience in animal health and welfare. When not working with her own animals and tending her farm, Krishna is helping other animal owners with behavior or management issues and teaching neighboring farmers about Regenerative Agriculture practices.

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