Armored Fish

By | September 9, 2016

Also known as placoderms, the armored fish were the first fish to grow to a monstrous size, some reaching the size of modern sharks. They were also among the first fish with biting jaws, which they used as lethal weapons. For protection from each other, these prehistoric fish evolved suits of armor made of overlapping plates of bone.


Key features
■ Armor-plated bodies
■ Jaws with bony plates that served as teeth
■ Joints between armor plates allowed the jaws to open and the body to bend

Armored fish lived from the Late Silurian Period, nearly 430 million years ago, to the end of the Devonian Period, 359 million years ago.

Dunkleosteus (DUN-kell-OSS-tee-us)


MONSTER JAWS: Dunkleosteus had a massive head and large, scissorlike jaws with razor-sharp bony plates that formed a “beak.” Its bite was powerful enough to crack concrete.

When: Nearly 380 million years ago (Late Devonian)

Fossil location: USA, Europe, Morocco

Habitat: Shallow seas

Length: 20 ft (6 m)


Reproduction of a dunkleosteus’s head

Sometimes described as the Tyrannosaurus of the seas, Dunkleosteus was one of the largest armored fish. It was as big as an elephant and a vicious hunter, with the most powerful bite of any fish (except perhaps the megatooth shark). Instead of teeth, Dunkleosteus had a kind of beak formed of bony plates with sharp points. Some Dunkleosteus fossils have bite marks matching these jaws, suggesting the killer was also a cannibal.

Gemuendina (JEM-yoo-en-DEE-na)


When: Almost 410 million years ago (Early Devonian)

Fossil location: Germany

Habitat: Shallow seas

Length: 10–12 in (25–30 cm)

A small, flat-bodied fish with a narrow tail, Gemuendina looked similar to the modern stingray except that its mouth was on top of its head. Unlike other armored fish, it did not have plates of bone in its mouth. Instead, it used star-shaped scales to grasp prey.

Coccosteus (cock-oh-STEE-us)


When: 380–350 million years ago (Middle to Late Devonian)

Fossil location: N. America, Europe

Habitat: Shallow waters

Length: 16 in (40 cm)

Although quite small in size, Coccosteus was an effective predator. It hunted other fish, perhaps lying in wait on the seabed for its prey before ambushing. Like Dunkleosteus, it had a beaklike mouth, with sharp, bladelike edges to tear flesh off larger animals. Its fossils show that it had a powerful tail, suggesting that it was a strong swimmer.

Rolfosteus (ROLL-foss-tee-us)


When: 380 million years ago (Late Devonian)

Fossil location: Australia

Habitat: Reefs

Length: 12 in (30 cm)

Rolfosteus was quite bizarre to look at, with a long, tubelike snout like a unicorn’s horn. Scientists are puzzled over the use of the snout. Rolfosteus may have used it to dig through the sandy seabed to look for hidden prey, or it may have been a male ornament used to attract females. Like other armored fish, this creature had no teeth. Instead, it had flattened plates of bone at the back of its mouth. These may have been used to crush the shells of crabs and other crustaceans.


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