Name: Dinichthys ‭(‬Terrible fish‭)‬.
Phonetic: Di-nik-fiss.
Named By: John Strong Newberry‭ ‬-‭ ‬1873.
Synonyms: Ponerichthys.
Classification: Chordata,‭ ‬Placodermi,‭ ‬Arthrodira,‭ ‬Dinichthyloidea.
Species: D.‭ ‬hertzeri,‭ ‬sometimes spelled herzeri‭ (‬type‭)‬.
Diet: Carnivore/Piscivore.
Size: Uncertain because only the head portions are known,‭ ‬possibly up to the same size as Dunkleosteus.
Known locations: USA,‭ ‬Canada.
Time period: Givetian through to Famennian of the Devonian.
Fossil representation: Well-known but only from the jaws and bony head armour.

       Like with may early discovered prehistoric animals such as the dinosaur Megalosaurus,‭ ‬and the pterosaur Pterodactylus,‭ ‬Dinichthys suffered from the waste basket taxon effect.‭ ‬This is where sets of remains that look similar to the holotype are assigned to the genus,‭ ‬but upon closer inspection they turn out to actually represent different animals.‭ ‬This has resulted in the long list of Dinichthys species being split up into separate genera including Eastmanosteus,‭ ‬Titanicthys,‭ ‬and the increasingly famous Dunkleosteus.‭ ‬Today only the original type species of Dinichthys hertzeri‭ (‬sometimes spelled as herzeri‭) ‬remains valid for the genus.
       As an armoured placoderm fish Dinichthys would have been an apex predator at the top of the food chain.‭ ‬Sharks were still very small in comparison,‭ ‬and the giant marine reptiles would not start appearing until the Triassic period.‭ ‬Many of the placoderm fish had hard bony plates and the sharp powerful jaws of Dinichthys were an effective counter to this armour.‭ ‬Biomechanical studies have revealed the related Dunkleosteus to have a multi-ton bite force,‭ ‬and it's perfectly reasonable to expect the same proportional bite force in Dinichthys.
       Dinichthys had the same kind of bony armour itself,‭ ‬although it appears that from fossil evidence of both Dinichthys and the predatory placoderm group in general that this armour was only present upon the head and jaws.‭ ‬It may be that instead of being there for protection,‭ ‬the bony plates provided rigid fixing and support for the powerful biting muscles.
       Dinichthys is often confused with Dunkleosteus because of their similar appearance,‭ ‬and this is not helped by the fact that reproductions of Dinichthys were for a long time based upon D.‭ ‬terrelli,‭ ‬the species that was split from Dinichthys to form the Dunkleosteus genus.

Further reading
- Notes on Dinichthys terrelli with a restoration - The Ohio Naturalist 8 (8): 363–369 - E. B. Benson - 1908.
- 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 & V. J. Hlavin - 2010.


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