Fossils of Henodus chelyops were found in the Estherienschichten Member of the Grabfeld Formation, near Tübingen, Germany.

[2][3] Henodus is the only placodont thus far found in non-marine deposits, suggesting it may have lived in brackish or freshwater lagoons.

[4] The armor was fused to its spine, and its limbs were situated in normal positions, unlike the turtle, where they are located inside the ribcage.

More recently, however, it has been suggested that this placodont was an aquatic herbivore, scraping off vegetation from the bottom with its broad jaws.

This suggestion has been brought up in a paper discussing the habits and morphology of Atopodentatus, another Mesozoic aquatic reptile formerly suggested to be a filter-feeder and bearing strongly convergent jaw adaptations, including a similar "hammerhead" jaw tips, though unlike Atopodentatus it's still believed that Henodus relied on filter feeding to obtain plant-matter from the substrates.