Placoderms are vertebrate animals of the class Placodermi, an extinct group of prehistoric fish known from Paleozoic fossils during the Silurian and the Devonian periods. While their endoskeletons are mainly cartilaginous, their head and thorax were covered by articulated armoured plates, and the rest of the body was scaled or naked depending on the species.
Dunkleosteus is an extinct genus of large arthrodire ("jointed-neck") fish that existed during the Late Devonian period, about 382–358 million years ago. It was a pelagic fish inhabiting open waters, and one of the first apex predators of any ecosystem.
Coccosteus is an extinct genus of arthrodire placoderm from the Devonian period. Its fossils have been found throughout Europe and North America. The majority of these have been found in freshwater sediments, though such a large range suggests that they may have been able to enter saltwater. It was a small placoderm, with Coccosteus cuspidatus measuring 29.6–39.4 cm (11.7–15.5 in) long.
Titanichthys is an extinct genus of giant, aberrant marine placoderm from shallow seas of the Late Devonian of Morocco, Eastern North America, and possibly Europe. Many of the species approached Dunkleosteus in size and build. Unlike its relative, however, the various species of Titanichthys had small, ineffective-looking mouth-plates that lacked a sharp cutting edge. It is assumed that Titanichthys was a filter feeder that used its capacious mouth to swallow or inhale schools of small, anchovy-like fish, or possibly krill-like zooplankton, and that the mouth-plates retained the prey while allowing the water to escape as it closed its mouth. A study has since confirmed this assumption as its jaws are functionally closer to that of filter feeders like baleen whales and basking sharks, and it appears to have developed from benthic durophagists that became pelagic suspension feeders. This would make it the first (known) large-sized vertebrate filter feeder. Titanichthys was estimated to have reached a length of 7–7.6 m (23–25 ft), but Engelman (2023) suggested that Titanichthys was comparable in size to Dunkleosteus, likely measuring about or just over 4.1 metres (13.5 ft) in length.
Heintzichthys is an extinct monospecific genus of arthrodire placoderm that lived what is now Europe and North America during the Famennian stage of the Late Devonian period. The type specimen was discovered in the Cleveland Shale near Cleveland, Ohio, in the United States.
Phyllolepis is the type genus of Phyllolepida, an extinct taxon of arthrodire placoderm fish from the middle to late Devonian. The species of Phyllolepis, themselves, are restricted to the Famennian-aged freshwater strata of the Late Devonian, around 360 million years ago. Fossils of this genus have been found primarily in Europe and North America. The end of the Devonian saw them disappear in a mass extinction.
Austrophyllolepis is an extinct genus of phyllolepid arthrodire placoderm from Middle to Late Devonian freshwater strata of Australia. The type species, A. ritchiei is found in Givetian to early Frasnian-aged freshwater strata near what is now Mount Howitt. A second species, A. dulciensis, is found from Middle Devonian freshwater strata from the Dulcie Sandstone of Georgina Basin, Central Australia.
Incisoscutum is an extinct genus of arthrodire placoderm from the Early Frasnian Gogo Reef, from Late Devonian Australia. The genus contains two species I. ritchiei, named after Alex Ritchie, a palaeoichthyologist and senior fellow of the Australian Museum, and I. sarahae, named after Sarah Long, daughter of its discoverer and describer, John A. Long.
Selenosteidae is an extinct family of small to large-sized arthrodire placoderms from the Late Devonian. With the exception of the Chinese Phymosteus, selenosteids lived in shallow seas in what is now Eastern North America, Eastern Europe, and Northeastern Africa.
Stenosteus is an extinct monospecific genus of medium-sized selenosteid arthrodire placoderms of the Late Devonian period known from the Upper Famennian Cleveland Shale of Ohio. Estimated skull lengths range from 6 to 9 centimeters Most fossils of Stenosteus have been scraps of armor and portions of tooth-plates suggestive of Selenosteus. In 1996, enough material of a new species, S. angustopectus, was recovered to allow a reconstruction of armor that resembles that of Selenosteus.
Gymnotrachelus is an extinct monospecific genus of large selenosteid arthrodire placoderm of the Late Devonian known from the Late Famennian Cleveland Shale of Ohio. The type species Gymnotrachelus hydei was originally reconstructed as physically resembling Selenosteus, with slightly smaller orbits. Later specimens led to a reappraisal, and now G. hydei is thought to have a more gar-like or barracuda-like build.
Rhinosteus is an extinct genus of small to medium selenosteid arthrodire placoderms of the Late Devonian known from the Upper Frasnian Kellwasserkalk facies of Bad Wildungen, Germany and Morocco.
Homostiidae is a family of flattened arthrodire placoderms from the Early to Middle Devonian. Fossils appear in various strata in Europe, Russia, Morocco, Australia, Canada and Greenland.
Coccosteidae is a family of arthrodire placoderms from the Early to Late Devonian. Fossils appear in various strata in Europe, North America and China.
Microbrachius is an extinct genus of tiny, advanced antiarch placoderms closely related to the bothriolepids. Specimens range in age from the Lower Devonian Late Emsian Stage to the Middle Devonian Upper Givetian Stage. They are characterized by having large heads with short thoracic armor of an average length of 2–4 cm. There are patterns of small, but noticeable tubercles on the armor, with the arrangement varying from species to species. Specimens of Microbrachius have been found in Scotland, Belarus, Estonia, and China.
Phymosteus liui is an extinct large selenosteid arthrodire placoderm known from the Lower Famennian Xiejingshi Formation of Shimen County, Hunan province, in central China.
Lehmanosteus is an extinct monospecific genus of arthrodire placoderm fish, named after French paleontologist Jean-Pierre Lehman. The type species Lehmanosteus hyperboreus was described in 1984, and was found in Early Devonian strata of the Wood Bay Formation on the island of Spitsbergen, Svalbard in Norway.
Herasmius is an extinct genus of heterosteid placoderm from the Devonian period. Fossils have been discovered freshwater deposits in Norway and Canada.
Kujdanowiaspis is an extinct genus of arthrodire placoderm fish from the Early Devonian of Podolia (Ukraine), Poland and Spain. Kujdanowiaspis is known from many fragmentary head shields and body armours.
The Junggar Basin, also known as the Dzungarian Basin or Zungarian Basin, is one of the largest sedimentary basins in Northwest China. It is located in Dzungaria in northern Xinjiang, and enclosed by the Tarbagatai Mountains of Kazakhstan in the northwest, the Altai Mountains of Mongolia in the northeast, and the Heavenly Mountains in the south. The geology of Junggar Basin mainly consists of sedimentary rocks underlain by igneous and metamorphic basement rocks. The basement of the basin was largely formed during the development of the Pangea supercontinent during complex tectonic events from Precambrian to late Paleozoic time. The basin developed as a series of foreland basins – in other words, basins developing immediately in front of growing mountain ranges – from Permian time to the Quaternary period. The basin's preserved sedimentary records show that the climate during the Mesozoic era was marked by a transition from humid to arid conditions as monsoonal climatic effects waned. The Junggar basin is rich in geological resources due to effects of volcanism and sedimentary deposition. According to Guinness World Records it is a land location remotest from open sea with great-circle distance of 2,648 km from the nearest open sea at 46°16′8″N86°40′2″E.
