Another anonymous request asked for a “terrestrial placoderm“:
Keluphichthys pezoporus is a descendant of Bothriolepis-like Devonian placoderms. Inhabiting shallow freshwater environments, they often used their rigid jointed fins to scramble short distances over land to reach new isolated ephemeral pools, and they developed convergently lung-like structures that could exchange gases directly from air, allowing them to survive in poorly-oxygenated waters and make even longer terrestrial journeys.
While the end-Devonian extinction devastated all other placoderms, this odd lineage survived into the Carboniferous, eventually raising themselves up to walk fully on their two limbs using a heavily scaled tail for balance.
Due to the relative weight of its bony carapace Keluphichthys is a fairly small animal, standing about 10cm tall (~4″). Its high domed body shape allows it to right itself when overturned, and resists the bite forces of larger predators such as the early tetrapods it lives alongside.
Its jaws are protrusible, with bony blades fused into a serrated “beak” used to snatch up invertebrate prey.
It’s still reliant on wet environments, needing to stay moist and returning to pools of water in order to reproduce. Juveniles start out aquatic and gradually transition to terrestrial habits as they mature.