Introduction: What Was Dunkleosteus? The Giant Armored Fish of the Devonian Seas

With an estimated maximum length of 3–8 meters (11–26 feet), Dunkleosteus terrelli was the largest known placoderm and one of the most formidable predators of the Late Devonian seas. Like all placoderms, D. terrelli possessed thick, interlocking bony armor that formed a protective “tank-like” shield over its head, jaws, and thorax. Unlike modern sharks, it lacked true teeth; instead, it used self-sharpening bony jaw plates capable of delivering an extraordinarily powerful bite.

A recent scientific reconstruction of this Devonian apex predator by Ferrón et al. (2017) is shown in the image near the top of this page.

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Dunkleosteus Species and Geographic Distribution

Dunkleosteus terrelli was the largest and best-studied species of the genus, but it was not the only one. Paleontologists recognize at least eight accepted species of Dunkleosteus, although several are based on fragmentary fossil remains.

Commonly cited valid species include: D. amblyodoratus, D. belgicus, D. denisoni, D. magnificus, D. missouriensis, D. newberryi, D. terrelli, and D. raveri. These species vary in size and fossil completeness, with D. terrelli remaining the most thoroughly documented.

A species discovered in Morocco, Dunkleosteus marsaisi, represents a possible occurrence in the southern Rheic Ocean. However, many researchers now classify this species within a different genus, Eastmanosteus marsaisi, based on anatomical differences.

Aside from the Moroccan material, all other confirmed Dunkleosteus species are known from North America (United States and Canada) and Western Europe. During the Late Devonian, these regions were connected within a shallow subtropical sea located north of the Rheic Ocean. This paleogeographic setting helps explain the distribution of Dunkleosteus fossils across what are today widely separated continents. In the map image below, this area is the subtropical sea north of the Rheic Ocean, which is the lighter blue area to the left of the "NA".

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What Did Dunkleosteus Look Like? Size, Anatomy, and Modern Reconstructions

Aside from a specimen preserving 20 associated vertebrae (Jackson et al., 2012) and a handful of fossils that retain portions of the pectoral fins (Carr et al., 2010), most Dunkleosteus specimens consist only of the thick armored plates that covered the head, jaws, and thorax. Because so little of the post-cranial skeleton has been preserved, reconstructing the full body shape of Dunkleosteus has long been a challenge for paleontologists.

Early reconstructions were modeled after a smaller placoderm called Coccosteus, which possessed similar-looking armored head plates. However, Coccosteus lived in freshwater environments and had a very different ecological lifestyle, making it an imperfect comparison for a massive marine predator like Dunkleosteus.

More recent reconstructions, particularly the study by Ferron et al. (2017), suggest that Dunkleosteus was adapted for pelagic swimming and active predation in open marine environments. The authors compared its inferred feeding and swimming habits to those of modern pelagic sharks and adjusted the body proportions accordingly. This interpretation is supported by Carr et al. (2010), who noted that preserved fin outlines more closely resemble those of chondrichthyans (sharks and their relatives) than previously assumed.

This modern pelagic-style reconstruction, which depicts a streamlined and powerful open-ocean predator, is shown near the top of this page.

Additionally, determining the true size of Dunkleosteus terrelli is challenging because most of the body is not preserved in the fossil record. Since only the armored head and thoracic plates are commonly found, scientists must estimate total length using scaling models and comparisons with other fishes. As a result, published size estimates vary considerably.

Carr (2010) estimated a large D. terrelli at a conservative 4.6 meters (15 feet) in length. Anderson and Westneat (2007) proposed a larger estimate of approximately 6 meters (19.6 feet).

Using a different approach, Ferrón et al. (2017) estimated body size based on jaw perimeter measurements and comparisons with modern pelagic sharks occupying similar ecological niches. Their reconstruction placed a very large specimen (CMNH 5936) at approximately 8.79 meters (28.8 feet). However, the authors cautioned that extreme estimates approaching 10 meters (33 feet) are likely overestimates.

More recently, Engelman (2023) proposed a substantially different reconstruction. Rather than adopting the streamlined pelagic body form suggested by Ferrón et al., Engelman returned to a more traditional, stout placoderm body plan. Under this interpretation, maximum body length estimates are significantly smaller, reaching approximately 3.34 meters (11 feet). This reconstruction is illustrated in the diagram at the top of this section.

So, at present, two primary body models dominate the discussion:

Pelagic shark-like reconstruction: Estimates commonly range around 6–9 meters (20–30 feet).
Traditional placoderm reconstruction: Maximum estimates are closer to 3–4 meters (10–13 feet).

This ongoing debate highlights how differences in body shape assumptions can dramatically influence total length estimates for Dunkleosteus.

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Dunkleosteus Jaws, Feeding Mechanics, and Record-Breaking Bite Force

Dunkleosteus terrelli was one of the first true apex predators in Earth’s history (Anderson & Westneat 2007), able to hunt almost any animal in its late Devonian ecosystem. Its dominance was driven both by its massive size and its specialized jaws. The bony plates forming its upper and lower jaws were shaped into fangs and sharp slicing edges. These jaws operated like self-sharpening blades, with the upper and lower plates shearing against each other with every bite.

Anderson and Westneat (2007) studied the feeding mechanics and bite force of Dunkleosteus jaws and discovered two key adaptations. First, the jaws could open and close extremely quickly, generating suction that pulled prey directly into the mouth. Second, the bite force was extraordinary—comparable to giant modern crocodiles. One large specimen, CMNH 5768, estimated at 6 meters (19.6 feet), exerted a bite force of 4,400 N (989 pounds) at the cusps and 5,300 N (1,200 pounds) at the tip of the jaw blade. This corresponds to a pressure of 147 million Pascals, or roughly 21,000 psi.

With this combination of suction and immense bite force, Dunkleosteus could easily crush armored prey, from thick-shelled ammonites to other placoderms. Evidence from Hall et al. (2016) shows scrape and puncture marks on armor belonging to other Dunkleosteus, indicating they may have occasionally preyed on one another.

Interestingly, the shape of Dunkleosteus jaws changed as individuals grew. Boyle et al. (2016) found that juvenile jaws were shorter with smaller anterior fangs, suited for hunting soft-bodied prey like fish and sharks. As the animal matured, the jaws elongated and the fangs became larger, allowing adults to tackle heavily armored prey such as other placoderms. This ontogenetic dietary shift is common among apex predators.

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Extinction of Dunkleosteus and the Late Devonian Mass Extinction

Dunkleosteus lived during the Late Devonian Period, approximately 385 to 359 million years ago. After its appearance in the fossil record, it diversified into multiple species and became one of apex marine predator of its time. However, despite its evolutionary success, Dunkleosteus did not survive the end-Devonian mass extinction events.

Two major extinction pulses occurred near the close of the Devonian: the Kellwasser Event, followed by the later and more severe Hangenberg Event. The Hangenberg Event, which occurred approximately 359 million years ago, is widely considered the terminal crisis of the Devonian Period. It devastated marine ecosystems worldwide and also significantly impacted early terrestrial vertebrates. Evidence shows that widespread ocean anoxia (oxygen depletion), rapid climate fluctuations, sea-level regression, and disruptions to nutrient cycles all contributed to ecosystem collapse. Reef systems disappeared, many fish lineages were eliminated, and entire groups of armored fishes vanished from the fossil record.

By the end of the Devonian Period, an estimated 70–80% of all species on Earth had gone extinct. Among the casualties were all placoderms, including Dunkleosteus, marking the end of these once-dominant armored fishes.

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Discovery of Dunkleosteus: Fossil Sites, History, and Scientific Naming

1867 – Original Discovery in Ohio
Dunkleosteus terrelli was first discovered in 1867 along the shale cliffs of Cove Beach in Sheffield Lake, Ohio, within the Cleveland Shale formation. Jay Terrell, a local hotel owner and avid fossil collector, frequently walked the shoreline fishing and searching for fossils with his son. That year, he uncovered massive armored plates belonging to a giant placoderm fish. Impressed by its size and appearance, he informally called it the “Terrible Fish.”

Over the following decades, additional armor fragments were recovered from the Devonian shales of northern Ohio, gradually revealing that this animal was one of the largest armored fishes ever found.

1928 - Rocky River Specimens and Major Excavations

In the 1920s, large-scale excavation of the Big Creek watershed began to improve regional drainage. Steam shovels cut deeply into the Cleveland Shale, exposing fossil-bearing concretions. Paleontologists from the newly established Cleveland Museum of Natural History (CMNH), including Peter Bungart and Jesse Earl Hyde, monitored the excavations and collected fossils directly from the site.

In 1928, at the Rocky River Reservation, Bungart and Hyde uncovered the largest and most complete specimen of the “Terrible Fish” known at that time. Over the next several years, Bungart painstakingly reconstructed the animal from numerous fragmented plates. Fortunately, Hyde documented the excavations with extensive photography, many of which are now preserved in the Hyde Collection. These historical images provide invaluable insight into early 20th-century fossil excavation methods.

1956 – Scientific Naming of Dunkleosteus terrelli
In 1956, the “Terrible Fish” was formally named Dunkleosteus terrelli. The genus name honors Dr. David Dunkle, a pioneering vertebrate paleontologist and early curator who conducted extensive research on the material. The species name recognizes Jay Terrell, the original discoverer of the fossil.

1965 – I-71 Construction and New Fossil Discoveries
Until the mid-20th century, most Dunkleosteus fossils were recovered from river systems draining into Lake Erie, especially the Rocky River. In the 1960s, construction of Interstate 71 cut through Big Creek Valley, exposing extensive layers of black Devonian shale representing the ancient seabed.

The Cleveland Museum of Natural History coordinated with the Ohio Department of Transportation to salvage fossils during highway construction. This effort yielded a wealth of new specimens, including sharks and additional placoderm species. Even today, the museum retains material from the I-71 excavations that continues to be prepared and studied.

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Below is a video from PBS Eons about Placoderms, including Dunkleosteus.

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Anderson, Philip & Westneat, Mark. (2007) Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator. Biology letters. 3. 76-9. 10.1098/rsbl.2006.0569. Publication here

Boyle, J. T., Ryan, M., Snively, E., and Hlavin, W. J. (2016) Jaw ontogeny of the late Devonian "T. rex" with implications for feeding strategies and life history of the arthrodire Dunkleosteus terrelli. Journal of Vertebrate Paleontology, Programs and Abstracts, 2016, 103. Poster here

Carr, Robert. (2010) The Cleveland Museum of Natural History PALEOECOLOGY OF DUNKLEOSTEUS TERRELLI (PLACODERMI: ARTHRODIRA). 57. 36-45. Publication here

Carr, Robert & Lelievre, Herve & L. Jackson, Gary. (2010) The ancestral morphotype for the gnathostome pectoral fin revisited and the placoderm condition. In: Morphology, Phylogeny and Paleobiogeography of Fossil Fishes: Honoring Meemann Chang, Publisher: Verlag Dr. Friedrich Pfeil, Editors: David K. Elliott, John G. Maisey, Xiaobo Yu, Desui Miao

Ferron, H. G., Martinez-Perez, C., & Botella, H. (2017) Ecomorphological inferences in early vertebrates: reconstructing Dunkleosteus terrelli (Arthrodira, Placodermi) caudal fin from palaeoecological data. PeerJ, 5, e4081. doi:10.7717/peerj.4081 Publication here

Hall, L., Ryan, M., and E. Scott. 2016. Possible evidence for cannibalism in the giant arthrodire Dunkleosteus, the apex predator of the Cleveland Shale Member (Fammenian) of the Ohio Shale. Journal of Vertebrate Paleontology, Programs and Abstracts, 2016, 148.

Jackson, G., Chapman, D., Boyle, J.T., Zelinski, D., Martin, T.G., Klunder, J.F., Reich, K., Reich, M., Robison, T.L. & Ryan, M.J. (2012) The most complete vertebral column of Dunkleosteus terrelli: results of the continuing Late Devonian Cleveland Shale (Famennian) fish research at the Cleveland Museum of Natural History. - 46th Annual Meeting (23-24 April 2012). Abstracts with Programs 44, No. 5: 66. Geological Society of America.

Richard Raponi, "Dunkleosteus," Cleveland Historical, accessed February 20, 2019, https://clevelandhistorical.org/items/show/728.

Russell K. Engelman. (2023) A Devonian Fish Tale: A New Method of Body Length Estimation Suggests Much Smaller Sizes for Dunkleosteus terrelli (Placodermi: Arthrodira). Diversity; 15 (3): 318 DOI: 10.3390/d15030318.

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FAQ's about the Dunkleosteus Article

• What is Dunkleosteus?
  Dunkleosteus was a large armored placoderm fish that lived during the Late Devonian Period, about 382–358 million years ago. It was an apex marine predator known for its thick head armor and powerful shearing jaw plates instead of true teeth.
• How big was Dunkleosteus?
  Recent research suggests Dunkleosteus terrelli likely reached about 11–13 feet (3.4–4 meters) in length. Earlier estimates proposed much larger sizes, but newer body-length reconstruction methods indicate it was smaller than traditionally thought.
• Was Dunkleosteus bigger than a great white shark?
  Most modern size estimates suggest Dunkleosteus terrelli reached 11–13 feet (3.4–4 meters), making it comparable to or smaller than large great white sharks. Earlier reconstructions depicted it as much larger, but recent studies support more moderate size estimates.
• Did Dunkleosteus have teeth?
  Dunkleosteus did not have true teeth. Instead, it possessed sharp, self-sharpening bony plates that formed powerful cutting edges within its jaws, allowing it to slice and crush prey efficiently.
• How strong was the bite of Dunkleosteus?
  Biomechanical studies estimate Dunkleosteus had a bite force of up to 8,000 pounds per square inch (about 55 megapascals), making it one of the most powerful bites of any known fish and capable of crushing armored prey.
• What did Dunkleosteus eat?
  Dunkleosteus was a carnivorous apex predator that likely fed on large fish, other placoderms, and marine invertebrates. Its powerful jaws and sharp bony plates allowed it to slice through flesh and crush hard armor.
• Where have Dunkleosteus fossils been found?
  Fossils of Dunkleosteus have been discovered in North America, Europe, and North Africa. Some of the most famous and complete specimens come from Late Devonian deposits in Ohio.
• Why did Dunkleosteus go extinct?
  Dunkleosteus went extinct during the Late Devonian mass extinction event, around 358 million years ago. This global marine crisis eliminated many reef ecosystems and apex predators, dramatically reshaping ocean life.

Dunkleosteus Article FAQ's

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