Dunklefish

Dunkleosteus is an extinct genus of large armored, jawed fish that existed during the Late Devonian period, about 358–382 million years ago. The type species was Dunkleosteus terrelli. The largest and most well-known species are found in North America, Poland, Belgium, and Morocco.

Etymology

Dunkleosteus was named by Jean-Pierre Lehman in 1956 to honour David Dunkle (1911–1984), former curator of vertebrate paleontology at the Cleveland Museum of Natural History. The genus name Dunkleosteus combines David Dunkle's surname with the Greek word ὀστέον (ostéon 'bone'), literally meaning "Dunkle's bone".

Physical Appearance

Dunkleosteus was covered in dermal bone, forming armor plates across its skull and the front half of its trunk. This armor is often described as being over 2–3 inches (5.1–7.6 cm) thick, but this is only across the thickened nuchal plate at the back of the skull. Thickening of the nuchal plate is a common feature of eubrachythoracid arthrodires. Across the rest of the body, the armor is generally much thinner, only about 0.33–1 inch (0.84–2.54 cm) in thickness. The plates of Dunkleosteus had both a hard cortical and a marrow-filled cancellous layer, unlike most teleost fishes and more similar to tetrapod bones.

Mainly, the armored frontal sections of specimens have been fossilized, and consequently, the appearance of the other portions of the fish is mostly unknown. In fact, only about 5% of Dunkleosteus specimens have more than a quarter of their skeleton preserved. Because of this, many reconstructions of the hindquarters are often based on fossils of smaller arthrodires, such as Coccosteus, which have preserved hind sections, leading to widely varying size estimates.

Dunkleosteus is one of the largest known placoderms, with its maximum size being variably estimated as anywhere from 4.1–10 meters (13–33 ft) by different researchers. However, most cited length estimates are speculative and lack quantitative or statistical backing, and lengths of 5 m (16 ft) or more are poorly supported. Most studies that estimate the length of Dunkleosteus do not provide information as to how these estimates were calculated, the measurements used to scale them, or which specimens were examined. Most are implied to be based on either CMNH 5768 (the largest complete armor of Dunkleosteus) or CMNH 5936 (the largest known jaw fragment).

According to Carr's (2010) estimation, an adult Dunkleosteus terrelli measuring 4.6 meters (15 feet) in length and weighing 665 kilograms (1,466 lb) was assumed to have a body plan comparable to that of a shark and a similar length-weight relationship. Using an ellipsoid volumetric technique, Engelman (2023) calculated weights of 2,090–2,650 lb for a typical adult Dunkleosteus measuring 3.41 meters (11.2 feet) in length and 1,494–1,764 kilos (3,294–3,889 lb) for the largest individual in the sample measuring 4.1 meters (13.5 feet). The main reason for the larger weights noted by Engelman (2023) is that, in comparison to sharks, arthrodires often have bodies that are wider and deeper.

Abilities

Dunkleosteus terrelli possessed a four-bar linkage mechanism for jaw opening that incorporated connections between the skull, the thoracic shield, the lower jaw, and the jaw muscles joined by movable joints. This mechanism allowed Dunkleosteus terrelli to both achieve a high speed of jaw opening, opening their jaws in 20 milliseconds and completing the whole process in 50–60 milliseconds (comparable to modern fishes that use suction feeding to assist in prey capture) and producing high bite forces when closing the jaw, estimated at 4,414 N (450 kgf; 992 lbf) at the tip and 5,363 N (547 kgf; 1,206 lbf) at the blade edge, or even up to 6,170 N (629 kgf; 1,387 lbf) and 7,495 N (764 kgf; 1,685 lbf), respectively. The bite force is considered the highest of any living or fossil fish and among the highest of any animal.

The pressures generated in those regions were high enough to puncture or cut through cuticle or dermal armor, suggesting that Dunkleosteus terrelli was adapted to prey on free-swimming, armored prey such as ammonites and other placoderms.

Ecology

Dunkleosteus, together with most other placoderms, may have also been among the first vertebrates to internalize egg fertilization, as seen in some modern sharks. Some other placoderms have been found with evidence that they may have been viviparous, including what appears to have been an umbilical cord.

Behavior

Dunkleosteus are mindless killers or lack intelligence, but the smell and hearing don't matter; many people would be surprised at their ability to learn and adapt. Despite their scary reputation, these armored fish rarely attack humans and would much rather feed on fish and marine mammals.

Dunkleosteus are cannibalistic fish, and they eat themselves, even their pups.

Distribution and Habitat

Fossilized remnants of Dunkleosteus terrelli can be found in Europe and the United States in the Upper Frasnian to Upper Famennian Late Devonian strata (the Ives breccia of Texas, the Conneaut and Chadakoin Formations of Pennsylvania, the Chattanooga Shale of Tennessee, the Lost Burro Formation of California, and the Huron, Chagrin, and Cleveland Shales of Ohio).

Movement Pattern: Nomadic
Individual Type: Solo
Population Trend: Stable
Population: 0
Locomotion: Aquatic
Habitat: All
Earth: Canada, United States

Tamed

Dunkleosteus cannot be tamed.

Lore

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