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. amblyodoratus, D. belgicus?, D. denisoni, D. magnificus, D.
marsaisi, D. missouriensis, D. newberryi, D. raveri.
Diet: Carnivore/Piscivore.
Size: Size estimated of largest fossils based upon certain
genera suggest largest size around 9 to maybe 10 meters long. However,
differing sizing methods suggest smaller body lengths for the same
fossils.
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 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.
- Ecomorphological inferences in early vertebrates: reconstructing
Dunkleosteus terrelli (Arthrodira, Placodermi) caudal fin from
palaeoecological data. - PeerJ. 5: e4081. - Humberto G. Ferrón, Carlos
Martínez-Pérez & Héctor Botella - 2017.
A Devonian Fish Tale: A New Method of Body Length Estimation Suggests
Much Smaller Sizes for Dunkleosteus terrelli (Placodermi: Arthrodira)".
Diversity. 15 (3): 318. - Russell K. Engelman - 2023.