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.
canadensis, C.
carbonarius, C. chamberlini, C. cuyahogae, C. decipiens, C. disjectus,
C. grossi , C. hercynius, C. macromus, C. markae, C. minor , C.
occidentalis, C. orvikui, C. terranovae.
Diet: Carnivore/Piscivore.
Size: Individuals around 30 to 43 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.