In those days, placoderms were thought to be shelled jawless fish akin to ostracoderms. Some naturalists even suggested that they were shelled invertebrates or even turtle-like vertebrates.

What is the nature of a Placoderm?

Most placoderms were small or moderate in size, but a few may have reached a length of 13 feet (4 metres). The name is derived from their characteristic armour of dermal, or skin, bones. This armour formed a head shield and a trunk shield, the two commonly connected by a paired joint in the neck region.

What are placoderms made of?

In general, placoderms are easily distinguished by their heavy armour made of large bony plates covering their head and thorax, and sometimes even their pectoral fins.