Placoderms
Placodermi is a class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devonian period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were among the first jawed fish; their jaws likely evolved from the first of their gill arches.
Generally speaking, any aquatic animal having fins and gills is considered a "fish." Nevertheless, because it includes a wide variety of animals, some of which are devoid of jaws or bone skeletons, this definition is essentially typological and not always phylogenetic (based on the evolutionary history and relationships between species). Along with the seas, practically every body of water has fish. While the current species count of fish exceeds 33,000, historically there were more species than there are now. Many lineages vanished entirely throughout time, leaving behind only fossilized remains and signs of their existence.
List of Placoderms
Arthrodires (Arthrodira)
The Arthrodira (Greek for "jointed neck") is an order of former extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine ecological niches. Arthrodires were the largest and most diverse of all groups of placoderms.
†Dunklefish (Dunkleosteus terrelli)
†Dunkleosteus denisoni
†Dunkleosteus marsaisi
†Dunkleosteus magnificus
†Dunkleosteus missouriensis
†Dunkleosteus newberryi
†Dunkleosteus amblyodoratus
†Dunkleosteus raveri
†Dunkleosteus tuderensis
†Robustberryfish (Coccosteus cuspidatus)
†Coccosteus canadensis
†Coccosteus carbonarius
†Coccosteus chamberlini
†Coccosteus cuyahogae
†Coccosteus decipiens
†Coccosteus disjectus
†Coccosteus grossi
†Coccosteus hercynius
†Coccosteus macromus
†Coccosteus markae
†Coccosteus minor
†Coccosteus occidentalis
†Coccosteus terranovae
†Xiangshuiosteus wui
Antiarchs (Antiarchi)
The Antiarchi ("opposite anus") is an order of heavily armored placoderms. The antiarchs form the second-most successful group of placoderms after the arthrodires in terms of numbers of species and range of environments.
†Canadian Armored Antiarchfish (Bothriolepis canadensis)
†Yunnanolepis chii
†Parayunnanolepis xitunensis
Rhenanids (Rhenanida)
The Rhenanida (Latin for ""Rhine's fish") is an order of scaly placoderms. Unlike most other placoderms, the rhenanids' armor was made up of a mosaic of unfused scales and tubercles.
†Gemuendina stuertzi
Asterosteus stenocephalus
Nefudina qalibahensis
†Jagorina pandora