Old Red Sandstone, abbreviated ORS, is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the eastern seaboard of North America. It also extends northwards into Greenland and Svalbard. These areas were a part of the paleocontinent of Euramerica (Laurussia). In Britain it is a lithostratigraphic unit to which stratigraphers accord supergroup status and which is of considerable importance to early paleontology. The presence of Old in the name is to distinguish the sequence from the younger New Red Sandstone which also occurs widely throughout Britain.
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.
Bothriolepis was a widespread, abundant and diverse genus of antiarch placoderms that lived during the Middle to Late Devonian period of the Paleozoic Era. Historically, Bothriolepis resided in an array of paleo-environments spread across every paleocontinent, including near shore marine and freshwater settings. Most species of Bothriolepis were characterized as relatively small, benthic, freshwater detritivores, averaging around 30 centimetres (12 in) in length. However, the largest species, B. rex, had an estimated bodylength of 170 centimetres (67 in). Although expansive with over 60 species found worldwide, comparatively Bothriolepis is not unusually more diverse than most modern bottom dwelling species around today.
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.
Phyllolepida is an extinct taxon of flattened placoderms found throughout the world, with fossils being found in Devonian strata. Like other flattened placoderms, the phyllolepids were bottom-dwelling predators that ambushed prey. Unlike other flattened placoderms, the phyllolepids were inhabitants of freshwater environments.
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.
Homosteus is a genus of flattened arthrodire placoderm from the Middle Devonian. Fossils are found primarily in Eifelian-epoch aged strata of Europe, Canada, Greenland, and Estonia. All of the species had comparatively large, flattened heads with, as suggested by the upward opening orbits, upward-pointing eyes. These adaptations suggest that the various species were benthic predators. A study on Titanichthys, in contrast, suggests that species of Homosteus may have been filter-feeders instead.
Gavinaspis is a phyllolepid placoderm which lived during the Early Devonian period, of Qujing, Yunnan province, south China.
Huginaspis is an extinct genus of placoderm arthrodire fish which lived during the Middle Devonian period of Spitsbergen, Norway.
Phyllolepididae is one of two families of phyllolepid placoderms. The family, as a whole, is believed to be descended from the Chinese placoderm, Gavinaspis (which forms the other, monotypic family, "Gavinaspididae"). All but two genera are, more or less, restricted to freshwater habitats of the Early to Middle Devonian of Australia. By the Frasnian, the genus Placolepis would spread throughout the world, with fossils being found in Australia, Turkey, Venezuela, and Antarctica, and by the start of the Famennian, phyllolepids would become extinct in Australia, with only species of Phyllolepis surviving in freshwater environments of Europe and North America.
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.
Microbrachiidae is an extinct family of tiny, advanced antiarch placoderms closely related to the bothriolepidids.
Angarichthys hyperboreus is an extinct homostiid arthrodire placoderm from the Middle Devonian of Siberia. It is known from an infragnathal plate, an intero-lateral plate, and a marginal plate found from the Middle Devonian strata of the Tynep Series formation, in the Bakhta River basin, Tunguska Plateau. A. hyperboreus differs from Homosteus in that the former's marginal plate has a ridge where the central plate would have overlapped it, and in the infragnathal, which is curved sigmoidally, and bears at least seven tooth-like prongs nearer to the functional anterior end.
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.
Placolepis is an extinct genus of phyllolepid placoderm first discovered in New South Wales. Placolepis was the most widespread phyllolepid genus, with fossils found in Australia, Turkey, Venezuela and Antarctica.
Yurammia is a placoderm from what is now the Pambula River in New South Wales. Unlike all other known phyllolepids, Yurammia's plates had no external grooves.
Cowralepis is an extinct genus of phyllolepid placoderm of Givetian Cowra, New South Wales, and several juveniles of various stages of growth have also been discovered. Cowralepis grew to 35 centimeters.
Cobandrahlepis is an extinct genus of phyllolepid placoderm found in New South Wales, Australia.
The Bokkeveld Group is the second of the three main subdivisions of the Cape Supergroup in South Africa. It overlies the Table Mountain Group and underlies the Witteberg Group. The Bokkeveld Group rocks are considered to range between Lower Devonian (Lochkovian) to Middle Devonian (Givetian) in age.
