Named By: Miller ex Agassiz - 1841.
Classification: Chordata, Placodermi, Arthrodira, Coccosteidae.
Species: C. cuspidatus (type). C. decipiens.
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.
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
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.