Ptyctodontida

The ptyctodontids ("folded-teeth") are a group of ancient fish called placoderms that belonged to the order Ptyctodontida. They had big heads, big eyes, long bodies, and very little armor, which made them look a bit like modern fish called Holocephali. Instead of heavy plates covering their bodies, they only had small plates around their heads and necks. Scientists think most of them lived near the ocean floor and ate shellfish.

Because ptyctodontids had so little armor, some scientists wondered if they were not really placoderms at all, but maybe a type of elasmobranch fish or even the ancestors of holocephalians. However, careful studies of their fossils show important differences. For example, unlike holocephalians, ptyctodontids did not have special skin called shagreen, their armor was made of bone not dentine, and they had beak-like tooth-plates instead of true teeth.

One interesting fact about ptyctodontids is that they were the only known placoderms that showed differences between males and females. Male ptyctodontids had special hook-like growths on their pelvic fins, similar to structures in male sharks and chimaeras. This suggests that these ancient fish might have used these hooks during mating.

Genera

The Ptyctodontidae family includes several groups, or genera, of ancient fish. Some of these groups are:

• Genus Austroptyctodus
• Genus Borysthenoplax
• Genus Campbellodus
• Genus Chelyophorus
• Genus Ctenurella
• Genus Denisonodus
• Genus Desmoporella
• Genus Eczematolepis
• Genus Goniosteus
• Genus Kimbryanodus
• Genus Materpiscis
• Genus Meeksiella
• Genus Palaeomylus
• Genus Ptyctodopsis
• Genus Ptyctodus
• Genus Rhamphodopsis
• Genus Rhynchodus
• Genus Tollodus