Dunkleosteus

Name: Dunkleosteus ‭(‬Dunkle's bone‭)‬.
Phonetic: Dun-kel-os-tee-us.
Named By: Lehman‭ ‬-‭ ‬1956.
Synonyms: Dinichthys terrelli, Ponerichthys.
Classification: Chordata,‭ ‬Placodermi,‭ ‬Arthrodira,‭ ‬Dunkleosteidae.
Species: D.‭ ‬terrelli‭ (‬type‭)‬,‭ ‬D.‭ ‬amblydoratus,‭ ‬D.‭ ‬marsaisi,‭ ‬D.‭ ‬raveri.
Diet: Carnivore/Piscivore.
Size: Up to‭ ‬10‭ ‬meters long.
Known locations: Canada.‭ ‬USA.‭ ‬Europe.‭ ‬Morocco.
Time period: Famennian of the Devonian.
Fossil representation: Several specimens,‭ ‬but only the bony head and jaws are known.

       In modern popular culture,‭ ‬Dunkleosteus is by far the best known and most often represented of the early placoderm carnivores.‭ ‬However Dunkleosteus actually sat within the Dinichthys genus for a long time as the species Dinichthys terrelli.‭ ‬It was not until the large numbers of Dinichthys remains were re-studied that it was realised that a large number of the Dinichthys fossils actually represented different genera,‭ ‬not species.‭ ‬The result was that many of these remains were split to form new genera including the creation of Dunkleosteus.‭ ‬In a further twist however,‭ ‬the species that was split to form Dunkleosteus,‭ ‬D.‭ ‬terrelli,‭ ‬was actually the remains most often used when reconstructing Dinichthys.‭
       Along with the equally giant Titanichthys,‭ ‬Dunkleosteus is one of the largest predatory placoderm fish known in the fossil record.‭ ‬However unlike Titanichthys which seems to have preferred large quantities of smaller prey items,‭ ‬Dunkleosteus was an apex predator capable of taking down pretty much anything it could clasp its jaws around.
       Because only the armoured head of Dunkleosteus is known,‭ ‬it can be problematic to reconstruct the rear portion that was almost certainly unarmoured.‭ ‬This reasoning comes about from the lack of rear fossils for not just Dunkleosteus but all related placoderms that are similar to Dunkleosteus.‭ ‬The only possible insights come from much smaller placoderms like Coccosteus.‭ ‬With a maximum length approaching only forty centimetres,‭ ‬Coccosteus was positively tiny in comparison to Dunkleosteus,‭ ‬but the impressions of the softer hind body can still be seen in fossils attributed to it.‭ ‬Smaller animals in general tend to fossilise better and in more complete states because they can get protected from scavengers and the elements more quickly.
       Aside from armour,‭ ‬the bony plates of Dunkleosteus could have served two further purposes.‭ ‬As a predatory placoderm,‭ ‬Dunkleosteus likely attacked other related placoderms that had the same kind of bony plates for protection.‭ ‬In the absence of a harder organic material,‭ Dunkleosteus would at least need the same material to break through the armour.‭ ‬Shape the material to a sharp bladed edge,‭ ‬and you have a chance of cutting through it.‭ ‬The second reason is that the jaws need enough driving power to cut and break apart armoured prey,‭ ‬and the only way that this could happen is if Dunkleosteus had incredibly powerful jaw muscles.‭ ‬However these muscles would in turn require strong supports and attachments otherwise the jaws could not be brought to bear with their full force.‭ ‬This is likely why Dunkleosteus and other related placoderms like Eastmanosteus retained armoured heads.
       Although Dunkleosteus had a powerful bite it was not the strongest amongst fish,‭ ‬that title goes to the gigantic shark C. megalodon that lived several hundred million years later.‭ ‬Still,‭ ‬with a bite force estimated at almost two metric tons,‭ ‬Dunkleosteus could still use its sharp jaws to shear through any prey item it chose.‭ ‬What prey items were on the menu seem to have been dependent upon the age of the Dunkleosteus in question.‭ ‬Juvenile Dunkleosteus had stiff jaws best suited for soft bodied prey items.‭ ‬As Dunkleosteus grew older,‭ ‬the jaws would become more flexible,‭ ‬perhaps to better protect them from injury and breakage when dealing with larger,‭ ‬more powerful and more heavily armoured prey items.
       The actual hunting and feeding style of Dunkleosteus is also a popular subject of interest.‭ ‬With the heavy plates around the head,‭ ‬Dunkleosteus was probably not a fast swimmer,‭ ‬but still would have had powerful muscles developed from just swimming around with the weight.‭ ‬This meant that Dunkleosteus either preferred slower prey,‭ ‬or used ambush tactics to try and take its prey off guard.‭ ‬Another thing to consider is that the jaws of Dunkleosteus,‭ ‬and probably other similar placoderms,‭ ‬could open exceptionally fast within a fraction of a second.‭ ‬This would create a sudden void inside the mouth of Dunkleosteus,‭ ‬creating a vacuum that sucked the water and the prey that was swimming in it into its mouth.‭ ‬This means that Dunkleosteus did not have to physically catch its prey,‭ ‬just get close enough to open its mouth.
       Larger Dunkleosteus seemed to have preferred other placoderm fish perhaps like Bothriolepis that was very common at the time.‭ ‬Once caught,‭ ‬Dunkleosteus could use its sharp jaws to cut up prey,‭ ‬but it seems that only the softer and more easily digestible flesh was desired.‭ ‬When Dunkleosteus fossils are found,‭ ‬they are often found in association with fish boluses.‭ ‬A bolus is a ball of remains that has been chewed and swallowed,‭ ‬but the remains in connection with Dunkleosteus are of only bones that already seem to have been partially digested.‭ ‬This indicates that Dunkleosteus may have spat out parts that were too hard for it to digest completely,‭ ‬a precedent that is known in numerous other fish.
       Finally,‭ ‬because Dunkleosteus was at the top of its food chain,‭ ‬the only other thing that it would have to worry about being attacked by was another Dunkleosteus.‭ ‬This actually does seem to have happened with some Dunkleosteus plates actually showing damage that seems to have been inflicted by the jaws of another Dunkleosteus.‭ ‬Asides from territorial combat,‭ ‬this may indicate active cannibalism in Dunkleosteus.

Further reading
- Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator - Royal Society 3 (1): 77–80 - Philip Anderson & Mark Westneat - 2007.
- Shape variation between arthrodire morphotypes indicates possible feeding niches - Journal of Vertebrate Paleontology volume 28, #4. - Philip S. L. Anderson - 2008.
- Two new species of Dunkleosteus Lehman, 1956, from the Ohio Shale Formation (USA, Famennian) and the Kettle Point Formation (Canada, Upper Devonian), and a cladistic analysis of the Eubrachythoraci (Placodermi, Arthrodira) - Zoological Journal of the Linnean Society 159(1):195-222 - R. K. Carr & W. J. Hlavin - 2010.



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