THE GIANT PLACODERM FISH DUNKLEOSTEUS AND TITANICHTHYS

The first fishes were the Ordovician/Silurian jawless agnathans, which gave rise to sharks and their kin. By the Devonian Period, they had an armour-plated head/thorax region, and, although, they lacked true teeth, their mouths had sharp bones that acted like teeth. During their apex, placoderms were widespread and dominated the seas, rivers, and lakes. They went extinct at the end of the Devonian Period 360 million years ago (mya) (Long, 1995). 

At least two placoderms were the first creatures to reach gigantic lengths of reportedly 8 m or more, but these total lengths are only estimates because the posterior portions of these “giants” are not preserved. The giant placoderms are Dunkleosteus (pronounced dun-kel-os-tee-us) and Titanichthys (pronounced titan-ick-theez). Both were arthrodire placoderms and belong to the dinichthyids: “meaning “terrible fish.” Until dinosaurs evolved, these two placoderms taxa were the first creatures to reach gigantic sizes. 

Dunkleosteus:

Discovered in 1867, 10 species reported.

Family Dunkleosteidae

Late Devonian (Famennian Age) (370 to 360 m.y.a)

Reportedly 13-30 feet (4 -10 m) long, but lengths greater than 16 feet (5 m) are estimated because only the head plates are currently known (the rest of their bodies are not preserved).

Two views (left side and front--oral) of Dunkleosteus, a rubber model made in 2006 by Safari, Ltd.

Known from USA (e.g., New York), Canada, Europe (Belgium and Poland), and Morocco.

Dunkleosteus most likely fed on anything available (e.g., brachiopods, bivalves, gastropods, trilobites, cephalopods, other placoderms, and earliest known sharks). The remains of this placoderm have been found with regurgitated fish remains.

Lived in shallow water as juveniles and ventured into the open ocean as adults.

Titanichtys:

discovered in 1885, 7 species reported.

family Titanichyidae

Late Devonian (Famennian Age) (370 to 360 mya)

Front side-view of Titanichtys.

Reportedly 23-25 feet (7-7.6 m) long; but lengths are estimated because only the head plates are currently known (the rest of their bodies are not preserved).

Known from Eastern North America, Morocco, and questionably Europe.

Titanichtys has only small plates in its mouth and lacks any sharp cutting edges. This placoderm might have been a filter feeder (ate plankton?), similar to the lifestyle of a basking shark.

References Used:

Long, J.A. 1995. The rise of fishes, 500 million years of evolution. The Johns Hopkins University Press, Baltimore and London. 223 pp.

prehistoric-wildlife.com   [for both genera]