Dunkleosteus

***Dunkleosteus*** (meaning "Dunkle's bone") was a large placoderm fish that lived in the late Devonian period, about 382–358 million years ago. It has been estimated to have grew to 4.1 metres (12.3 feet), and was the top predator of its time and the Paleozoic era as a whole.

## Description

*Dunkleosteus* belongs to the Placodermi, a large, paraphyletic clade of armor-plated fishes likely ancestral to all living gnathostomes. More precisely, it was an arthodire, part of a clade which possessed skulls that had two joints to open the mouth. *Dunkleosteus* remains have been found in late Devonian strata in Morocco, Belgium, Poland, and North America.

Three hundred fifty-eight million years ago, a shallow sea teeming with marine life covered Northeast Ohio. *Dunkleosteus terrelli*, the largest predator and one of the fiercest creatures alive in the Devonian “Age of Fishes,” ruled the subtropical waters. With estimates up to 20 feet in length and weighing more than 1 ton, this arthrodire fish was capable of chopping prehistoric sharks into chum! *Dunkleosteus* had a massive skull made of thick, bony plates, and 2 sets of fang-like protrusions near the front of powerful, self-sharpening jawbones.

*Dunkleosteus* could concentrate a force of up to 7,400 N at the tip of its mouth, effectively placing *Dunkleosteus* in the league of *Tyrannosaurus rex* and modern crocodiles as having the most powerful known bite. *Dunkleosteus* could also open its mouth in one-fiftieth of a second, which would have caused a powerful suction that pulled the prey into its mouth, a food-capture technique reinvented by many of the most advanced teleost fishes today.

Due to its heavily armoured nature, *Dunkleosteus* was likely a relatively slow (albeit powerful) swimmer. By Devonian standards, *Dunkleosteus* was one of the most highly evolved animals. It was one of the earliest jawed fishes. Instead of actual teeth, *Dunkleosteus* possessed a set of long, bony blades that were extensions of its jaw that could slice through flesh and snap and crush bones and almost anything else. These plates also sharpened themselves every time the fish closed its mouth, in a fashion somewhat similar to rodent teeth.

*Dunkleosteus terrelli* was the largest and most well studied species, however, there were many other smaller species. Although many are based on sparse and fragmentary remains, there have been at least 8 accepted species. The following species are often considered valid: *D. amblyodoratus, belgicus, denisoni, magnificus, missouriensis, newberryi, terrelli,* and *raveri*.

Previous reconstructions were based on a placoderm that was much smaller, but had similar looking body plates. This placoderm is called *Coccosteus*. Unfortunately, *Coccosteus* lived in fresh water and thus had a very different mode of life, so it probably looked different. More recently, a reconstruction by Ferron et al. 2017 used inferences from *Dunkleosteus* pelagic swimming and feeding habits. They noted their lifestyle was similar to that of a pelagic shark and adjusted the body morphology to suit. This is also in agreement with Carr et al. 2010, that states the preserved fin outlines are more like chondrichthyans (sharks). Additionally, the size of D. terrelli is difficult to pinpoint. Inferences must be made about most of the body. As a result, maximum sizes have varied. Carr 2010 places a large D. terrelli at very conservative 4.6 m (15 feet), while Anderson and Westneat 2007 places a large one at 6m (19.6 feet). In a more recent reconstruction attempts using jaw perimeter and pelagic sharks that had similar ecological niches, Ferron et al. 2017 places a very large specimen, CMNH 5936, at 8.79 m (28.8 feet). Although this estimate is large, Ferron et al. 2017 has a limit and says estimates of 10 meters are most likely overestimates.

A recent reconstruction has used relatives of the fish to more accurately portray the true size of the fish, significantly shortening it to a maximum of 4.1 meters, which makes its depiction fit far more nicely in the clade it belongs to. Despite the decrease in size, it was still the largest predator in the ecosystem and used its proportionally large armored head to hunt prey.

*Dunkleosteus* lived during the Late Devonian time period, from 385 to 359 mya. When *Dunkleosteus* appeared, it quickly diversified into many species, however, it could not survive the end Devonian mass extinction events. Two extinction events occurred at the end of the Devonian, the Kellwasser Event and later the Hangeberg Event. The last event, the Hangenberg event, wiped out both marine and terrestrial vertebrates. It completely destroyed many marine ecosystems. By the end of the Devonian, 70 to 80% of all species on Earth, including all placoderms were extinct, ending the reign of *Dunkleosteus*.

## Mouth & Jaws

*Dunkleosteus* may have had fleshy lips covering its teeth, making it resemble modern cetacean species like beluga whales. *Dunkleosteus terrelli* was one of the first true apex predators to appear on Earth (Anderson & Westneat 2007), meaning it could eat any animal it wanted and had very little predators due to its size and jaws. Bony plates making up the jaws were sculpted into fangs and long slicing edges. The upper and lower jaws would also shear against one another causing them to self-sharpen.

Moreover, Anderson and Westneat (2007) studied the feeding mechanics and the bite force of *Dunkleosteus terrelli* jaws. They made two key findings. First, they discovered the jaws could rapidly open and close. So fast that *Dunkleosteus* could make a suction when opening, sucking prey into it. Secondly, they found the jaws to have a tremendous bite force, on par with giant crocodiles. One of the larger specimens studied, CMNH 5768, which is estimated to be 6 meters in length had a bite force of 4,400 N (989 pounds) on the cusps and 5,300 N (1,200 pounds) on the end of the blade. Putting this in terms of pressure, this is 147 million Pascals or 21,000 psi (Anderson and Westneat 2007).

Combined, *Dunkleosteus* could suck in and bite straight through any animal alive at that time, from the thick shelled Ammonites, to other Placoderms with body armor. In fact, a study by Hall et al., 2016 found scrape and puncture marks on other *Dunkleosteus* armor that were made by larger *Dunkleosteus*. This means they may have even eaten eat other!

Another interesting fact is the jaw shape of *Dunkleosteus* changed as it grew from juvenile to adult. A study by Boyle et al. showed the jaw became more elongated and grew a longer anterior fang, or cusp. The study concludes as the animal grew, the diet shifted from soft-bodied prey, such as fish and sharks to larger armored prey, such as placoderms (Boyle at al 2016). This shift in diet is common in top predators as they grow from juvenile to adult.

## History

In 1966, the Ohio Department of Transportation (ODOT) began construction on Interstate 71 in the shale-rich Big Creek Valley—a treasure trove of sediment and fossil material. Under the leadership of then-Director William Scheele, a team of Museum researchers led by Bill Hlavin worked in collaboration with ODOT to excavate an immense volume of fossil-bearing shale concretions from the construction site. A rich variety of fossil fish and plants from the Late Devonian were uncovered, and continue to be found in the Cleveland Shale today!  The Museum has some of the world’s best-preserved Dunkleosteus terrelli fossils, including the giant armored skull on display in Kirtland Hall of Prehistoric Life, nicknamed “Dunk." *Dunkleosteus terrelli* is named for former Museum Curator of Vertebrate Paleontology Dr. David Dunkle and Jay Terrell, who discovered the first fossils of the “terrible fish” in 1867.

## Appearance in other media

### *Jurassic Park*

* It appears in Jurassic Park: Builder as the first creature in the Aquatic Park.
* *Dunkleosteus* appears in Jurassic World: The Game as a legendary cave creature in the aquatic park.
* *Dunkleosteus* makes an appearance in Jurassic World Evolution 2 via the Prehistoric Marine Species Pack released on August 10th, 2023.

## References

1. ↑ https://paleobiodb.org/classic/basicTaxonInfo?taxon\_no=421176
2. ↑ Anderson, P.S.L.; Westneat, M. (2009). "A biomechanical model of feeding kinematics for *Dunkleosteus terrelli* (Arthrodira, Placodermi)" (PDF). *Paleobiology*. **35** (2): 251–269. doi:10.1666/08011.1. S2CID 86203770.