Name: Coccosteus ‭(‬Seed Bone‭)‬.
Phonetic: Coc-co-stee-us.
Named By: Miller ex Agassiz‭ ‬-‭ ‬1841.
Classification: Chordata,‭ ‬Placodermi,‭ ‬Arthrodira,‭ ‬Coccosteidae.
Species: C.‭ ‬cuspidatus‭ (‬type‭)‬.‭ ‬C.‭ ‬decipiens.
Diet: Carnivore/Piscivore.
Size: Up to‭ ‬40‭ ‬centimetres long.
Known locations: North America.‭ ‬Europe.
Time period: Eifelian to Givetian of the Devonian.
Fossil representation: Many specimens of complete individuals.

       Although Coccosteus could reach up to forty centimetres in length it was often less than half this at just over twenty centimetres.‭ ‬This made Coccosteus smaller than some of the other larger placoderms that were prey to the really big hunters like Dunkleosteus and Dinichthys.‭ ‬However this small size is probably the reason why Coccosteus preserved better than its larger cousins,‭ ‬because it could be buried and protected from scavengers and the elements much more quickly.‭ ‬This more complete level of preservation has meant that Coccosteus has on many occasions been used as a model to reconstruct larger arthrodire placoderms were usually only the bony head plates are preserved.
       The mouth of Coccosteus has been found to have been capable of opening extremely wide,‭ ‬meaning that a greater number of potential prey items were on the menu.‭ ‬This movement was allowed by the presence of an additional joint in between the skull and neck vertebra.‭ ‬This combined with the usual joint between the skull and neck plates meant that the head of Coccosteus had a greater amount of up and down motion than other arthrodire placoderms.‭ ‬This action meant that a greater amount of water could be passed over the gills,‭ ‬and while it has been suggested by some that Coccosteus may have done so to filter organic material from the mud below,‭ ‬it may have also been done to help it breathe in water where the oxygen content was low.‭ ‬In this scenario even though the water oxygen content would be low,‭ ‬a greater amount of water over the gill would result in faster exposure to a greater amount.
       Like in other arthrodire placoderms the jaws were very sharp,‭ ‬a result of the dental plates constantly grinding against each other when the jaw was closed.‭ ‬The eyes were also much nearer the front of the head than they were in some other arthrodire placoderms,‭ ‬suggesting that Coccosteus had a greater reliance upon vision when hunting.
       Many of the Coccosteus remains have been confirmed to have come from fresh water environments,‭ ‬although it‭’‬s not completely out of the question that Coccosteus was active in saltwater as well.‭

Further reading
- On some new Fossil Fish of the Carboniferous Period. - The Annals and Magazine of Natural History, Second Series 2:1-10. - F. M'Coy - 1848.
- Catalogue of the Fossil Fishes in the British Museum (Natural History). Part II. - Catalogue of the Fossil Fishes in the British Museum (Natural History) 2. - A. S. Woodward - 1891.
- Lower Devonian Fishes of Bear Tooth Butte, Wyoming. - Proceedings of the American Philosophical Society 71(5):225-254. - W. L. Bryant - 1932.


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