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The Devonian is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at 419.2 million years ago (Ma), to the beginning of the succeeding Carboniferous period at 358.9 Ma. It is named after Devon, South West England, where rocks from this period were first studied.
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.
Arthrodira is an order of 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.
The Tetrapodomorpha are a clade of vertebrates consisting of tetrapods and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced forms transitional between fish and the early labyrinthodonts, such as Tiktaalik, have been referred to as "fishapods" by their discoverers, being half-fish, half-tetrapods, in appearance and limb morphology. The Tetrapodomorpha contains the crown group tetrapods and several groups of early stem tetrapods, which includes several groups of related lobe-finned fishes, collectively known as the osteolepiforms. The Tetrapodomorpha minus the crown group Tetrapoda are the stem Tetrapoda, a paraphyletic unit encompassing the fish to tetrapod transition.
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.
Gogonasus was a lobe-finned fish known from three-dimensionally preserved 380-million-year-old fossils found from the Gogo Formation in Western Australia. It lived in the Late Devonian period, on what was once a 1,400-kilometre coral reef off the Kimberley coast surrounding the north-west of Australia. Gogonasus was a small fish reaching 30–40 cm (1 ft) in length.
Brindabellaspis stensioi is a placoderm with a flat, platypus-like snout from the Early Devonian of the Taemas-Wee Jasper reef in Australia. When it was first discovered in 1980, it was originally regarded as a Weejasperaspid acanthothoracid due to anatomical similarities with the other species found at the reef.
Rolfosteus is an extinct monospecific genus of arthrodire placoderm from the Early Frasnian stage of the Late Devonian period, found at the Gogo Formation of Western Australia.
Onychodus is a genus of prehistoric lobe-finned fish which lived during the Devonian Period. It is one of the best known of the group of onychodontiform fishes. Scattered fossil teeth of Onychodus were first described from Ohio in 1857 by John Strong Newberry. Other species were found in Australia, England, Norway and Germany showing that it had a widespread range.
The Gogo Formation in the Kimberley region of Western Australia is a Lagerstätte that exhibits exceptional preservation of a Devonian reef community. The formation is named after Gogo Station, a cattle station where outcrops appear and fossils are often collected from, as is nearby Fossil Downs Station.
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.
Ligulalepis is an extinct genus of prehistoric bony fish. Ligulalepis was first described from isolated scales found in the Taemas-Wee jasper limestones of New South Wales by Dr Hans-Peter Schultze (1968) and further material described by Burrow (1994). A nearly complete skull found in the same general location was described in Nature by Basden et al. (2000) claiming the genus was closely related to basal ray-finned fishes (Actinopterygii). In 2015 Flinders University student Benedict King found a more complete new skull of this genus which was formally described by Clement et al. (2018), showing the fish to be on the stem of all osteichthyans.
Fallacosteus is an extinct monospecific genus of arthrodire placoderm from the Early Frasnian stage of the Late Devonian period, found at the Gogo Formation of Kimberley, Western Australia. As with almost all other camuropiscids, F. turneri had an elongated snout that may have enhanced its hydrodynamic streamlining.
Tubonasus is an extinct monospecific genus of long-snouted arthrodire placoderm from the Early Frasnian stage of the Late Devonian period, found at the Gogo Formation of Kimberley, Western Australia.
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish. Early examples include Haikouichthys. During the late Cambrian, eel-like jawless fish called the conodonts, and small mostly armoured fish known as ostracoderms, first appeared. Most jawless fish are now extinct; but the extant lampreys may approximate ancient pre-jawed fish. Lampreys belong to the Cyclostomata, which includes the extant hagfish, and this group may have split early on from other agnathans.
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.
Antarctilamna is an extinct genus of Devonian cartilaginous fish originally exemplified by Antarctilamna prisca from South Eastern Australia and Antarctica. The latest occurring described species is Antarctilamna ultima from the Waterloo Farm lagerstätte in South Africa. Antarctilamna has robust ctenacanthid-like spines which lack a deep insertion area, and are borne in front of the first dorsal fin; in addition to distinctive diplodont teeth with small intermediate cusps. Antarctilamna-like spines, known from the Bunga Beds locality in Australia have been ascribed to A. prisca.
Torosteus is an extinct genus of arthrodire placoderm from the Early Frasnian stage of the Late Devonian period. Fossils are found in the Kimberley region of Australia.
Phoebodus is an extinct genus of phoebodontiform total group elasmobranch, known from over a dozen species found worldwide spanning the middle to late Devonian, making it one of the oldest known total group elasmobranchs. Most species are only known from their isolated tricuspid teeth, but one species, Phoebodus saidselachus from the Late Devonian of Morocco, is known from a complete skeleton, estimated to have been 1.2 metres (3.9 ft) in total length in life, which shows that it had a slender body superficially similar to that of the living frilled shark. The teeth of Phoebodus and frilled sharks are also morphologically similar, and are designed for grasping prey. Phoebodus probably consumed small prey items that were capable of being swallowed whole.
References
- ↑ Zerina Johanson, John A. Long, John A. Talent, Philippe Janvier, James W. Warren (2006): "Oldest coelacanth, from the Early Devonian of Australia". Biology Letters. pp. 443–446.
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