Editing Placoderm (section)

====Ptyctodontida====
[[File:Kimbryanodus williamburyensis.jpg|thumb|left|''Kimbryanodus williamburyensis'']]
[[Ptyctodontida]] ("folded teeth") were lightly armoured placoderms with big heads, big eyes and long bodies. They have a strong but superficial resemblance to modern day [[chimaera]]s. Their armour was reduced to a pattern of small plates around the head and neck. Like the extinct and related [[acanthothoracids]], and the living and unrelated holocephalians, most of the ptyctodontids are thought to have lived near the sea bottom and preyed on [[shellfish]]. On account of their lack of armour, some paleontologists have suggested that the Ptyctodontida were not placoderms, but [[holocephalians]] or the ancestors of holocephalians. Anatomical examinations of whole fossil specimens have shown that the similarities between these two groups are superficial. The major differences were that holocephalians have [[shagreen]] on their skin, while ptyctodontids do not; the armoured plates and scales of holocephalians are made of [[dentine]], while those of ptyctodontids are made of bone; the craniums of holocephalians are similar to sharks, while those of ptyctodontids are similar to those of other placoderms; and, most importantly, that holocephalians have true teeth, while ptyctodonts have beak-like tooth plates. Ptyctodontids were [[sexually dimorphic]], with the males having pelvic [[clasper]]s and possibly claspers on the head as well.