About Dunkleosteus
| Scientific Name (Genus) | Dunkleosteus |
| Classification | Placodermi, Arthrodira, Dunkleosteidae |
| Total Length | Approx. 3.4m (Max approx. 4.1m) |
| Diet | Carnivorous |
| Period | Late Devonian (approx. 382 to 358 million years ago) |
| Sub-classification / Species Name | Dunkleosteus terrelli (Type species) and others |
| Year of Paper Publication | 1956 |
A group of fish that prospered during the Paleozoic era, covered in hard bony plates (armor) on their head and thorax. They are known as the first vertebrates to possess a jaw.
Review of Restored Appearance: From a Giant "Shark" to a "Tuna Shape"
Ibaraki Nature Museum
Dunkleosteus was a giant carnivorous fish that reigned in the late Devonian seas. However, its appearance and size have been significantly revised by recent research.
Only the hard armor plates of the head and thorax tend to remain as fossils, and because the body behind that was made of cartilage, fossils were rarely found. Therefore, for many years it was speculated that "it reached a total length of 6 to 10 meters and had a slender, shark-like body shape." It was also once grouped into another classification called "Dinichthys".
However, in a study published in 2023, comparing skeletal proportions such as the length from the eye to the gills (orbit-opercular length) with many other fish, the total length was revised downwards to about 3.4 meters for a typical adult, and about 4.1 meters even for the largest individuals. It also became clear that it had a short, stocky body shape like modern tunas and great white sharks, rather than a slender shark-like appearance.
Its body shape, with a thick torso and a crescent-shaped tail fin, was an evolution for swimming agilely in the vast ocean. The heavy-looking armor plates were actually lightweight, indicating that it was a hunter with high swimming abilities.
The Ultimate Weapon: High-Speed Opening Jaws and Self-Sharpening Blades
by Gemini.
Dunkleosteus lacked "teeth" like modern fish or sharks. Instead, the jawbone itself acted as a razor-sharp blade.
Furthermore, Dunkleosteus' jaw had a mechanism called a "four-bar linkage" that interlocked with the skull and chest armor. This allowed it to open its mouth wide at an incredible speed of just 0.02 seconds (20 milliseconds). It was once thought that this quick mouth movement was for "suction feeding," drawing in prey along with the surrounding water, but it is now estimated that it had a style of charging at prey, opening its mouth in an instant, and biting it off.
The biting force (bite force) when closing was also tremendous, reaching several thousand newtons in the largest individuals. This is a power comparable to Tyrannosaurus or large crocodiles, making it one of the strongest in fish history. With this tremendous force, it could crush the hard shells of ammonites and the bony armor of other fish.
While biting through hard objects seems like it would ruin the blades, Dunkleosteus' jaws were structured so that the upper and lower bone blades rubbed perfectly against each other every time it opened and closed its mouth. This ensured that the blade edge was constantly kept sharp.
Ecology in the Devonian Seas and Cannibalism
Dunkleosteus was an apex predator that migrated through the open oceans of the Late Devonian. It regurgitated indigestible bones from its stomach, and clumps of regurgitated fish bones (pellets) are sometimes found near fossils.
Its diet also changed as it grew. When young, it snapped its jaws shut quickly to eat small fish, but as it grew larger, the tip of its jaw became thicker and sturdier, and it began to target slower-moving but hard-shelled ammonites and other armored fish.
In addition, they were highly aggressive, and bite marks on fossils show that they routinely engaged in fierce intraspecific combat (cannibalism). Furthermore, rather than simply biting, they possessed advanced hunting tactics, accurately targeting "structural weaknesses" such as the joints in the armor and around the gills of their opponents.
Regarding reproduction, organs for copulation have been found in male fossils, and it is highly likely that they were "viviparous," undergoing internal fertilization like sharks and giving birth directly to relatively developed fry rather than laying eggs.
The Extinction of Dunkleosteus and the Following Era
Although Dunkleosteus ruled the seas as the ultimate predator, it went extinct due to a global environmental change known as the "Hangenberg Event" at the end of the Devonian period. The rapid cooling and ocean anoxia (oxygen depletion) caused by this event meant that highly active organisms consuming large amounts of oxygen could not survive.
The disappearance of placoderms, including Dunkleosteus, created an "ecological vacuum" in the sea, which subsequently led to a rapid diversification of shark relatives (chondrichthyans) and bony fish (actinopterygians).
Dunkleosteus Stamp and Fossil Gallery
