Titanichthys was a giant Devonian placoderm which was about twenty feet long. Since the tooth-like gnathal plates in its mouth were small and dull, it is believed that this fish fed on tiny zooplankton and tiny fish.
Fossils have been found in North America, Morocco, and Poland. Some specimens are found in the Cleveland Shale of Ohio, and shared the same area with Cladoselache, Dunkleosteus, and many other strange fish.
The fossil below shows the upper part of a Titanichthys skull. Although it doesn't look like it, it's a well-preserved specimen. The only downsides are that it does not preserve the bottom half of the skull, and it was flattened during fossilization. But what's amazing is that it's complete to a certain extent. The front of the skull is facing upwards, while the neck plates in the back of the skull are facing downwards. Also note the strange diamond-shaped hole in the middle of the skull. This is the neck joint that gave these so-called arthrodire placoderms their name. "Arthrodire" means "jointed neck."
Titanichthys was one of the largest placoderms. In fact, it was the second largest, after Dunkleosteus terrelli. When Titanichthys was first discovered, some scientists thought that the pieces of bone were from a dinosaur. But after more study, it was discovered that they were actually from a placoderm fish.