Editing Placoderm (section)

====Rhenanida====
[[File:Asterosteus stenocephalus.jpg|thumb|upright|''[[Asterosteus]]'']]
[[Rhenanida]] ("[[Rhine]] fish") were flattened, [[Batoidea|ray-like]], bottom-dwelling [[predator]]s with large, upturned mouths that lived in marine environments. The rhenanids were once presumed to be the most primitive, or at least the closest to the ancestral placoderm, as their armour was made of unfused components—a mosaic of tubercles—as opposed to the solidified plates of "advanced" placoderms, such as [[antiarch]]s and [[arthrodire]]s. However, through comparisons of skull anatomies, rhenanids are now considered to be the sister group of the antiarchs. When rhenanids die, their "mosaics" come apart, and it has been suggested that the rarity of rhenanids in the fossil record reflects postmortem disassociation, and is not an actual rarity of the species.