Dunkleosteus is an extinct genus of arthrodire placoderm fish that existed during the Late Devonian period, about 358–382 million years ago. The name Dunkleosteus combines the Greek osteus (οστεος), meaning "bone", and Dunkle, in honor of David Dunkle of the Cleveland Museum of Natural History. It consists of ten species: D. terrelli, D. belgicus, D. denisoni, D. marsaisi, D. magnificus, D. missouriensis, D. newberryi, D. amblyodoratus, and D. raveri; some of which are among the largest placoderms to have ever lived. The largest species, D. terrelli grew up to 6 m (19.7 ft) long and 1 t (1.1 short tons) in weight. Few other placoderms rivaled Dunkleosteus in size. Dunkleosteus could quickly open and close its jaw, like modern day suction feeders, and had a bite force of 6,000 N (612 kgf; 1,349 lbf) at the tip and 7,400 N (755 kgf; 1,664 lbf) at the blade edge. Numerous fossils of the various species have been found in North America, Poland, Belgium, and Morocco.
|Reconstructed skull, Vienna Natural History Museum|
Dunkleosteus was named in 1956 to honour David Dunkle, then curator of vertebrate paleontology at the Cleveland Museum of Natural History. The type species D. terrelli was originally described in 1873 as a species of Dinichthys. Dunkleosteus is an arthrodire originally placed in the family Dinichthyidae, which is composed mostly of large, carnivorous fish like Gorgonichthys. Anderson (2009) suggests, because of its primitive jaw structure, Dunkleosteus should be placed outside the family Dinichthyidae, perhaps close to the base of the clade Pachyosteomorpha, near Eastmanosteus. Carr and Hlavin (2010) resurrect Dunkleosteidae and place Dunkleosteus, Eastmanosteus, and a few other genera from Dinichthyidae within it. Dinichthyidae, in turn, is made into a monospecific family.
The type species, D. terrelli, is the largest, best-known species of the genus. It has a rounded snout. D. terrelli's fossil remains are found in Upper Frasnian to Upper Famennian Late Devonian strata of the United States (Huron and Cleveland Shale of Ohio, the Conneaut of Pennsylvania, Chattanooga Shale of Tennessee, Lost Burro Formation, California, and possibly Ives breccia of Texas) and Europe.
D. belgicus (?) is known from fragments described from the Famennian of Belgium. The median dorsal plate is characteristic of the genus, but, a plate that was described as a suborbital is apparently an anteriolateral plate.
D. denisoni is known from a small median dorsal plate, typical in appearance for Dunkleosteus, but much smaller than normal.
D. marsaisi refers to the Dunkleosteus fossils from the Lower Famennian Late Devonian strata of the Atlas Mountains in Morocco. It differs in size, the known skulls averaging a length of 35 centimetres (1.15 ft) and in form to D. terrelli. In D. marsaisi, the snout is narrower, and a postpineal fenestra may be present. Many researchers and authorities consider it a synonym of D. terrelli. H. Schultze regards D. marsaisi as a member of Eastmanosteus.
D. magnificus is a large placoderm from the Frasnian Rhinestreet Shale of New York. It was originally described as "Dinichthys magnificus" by Hussakof and Bryant in 1919, then as "Dinichthys mirabilis" by Heintz in 1932. Dunkle and Lane moved it to Dunkleosteus in 1971.
D. newberryi is known primarily from a 28 centimetres (11 in) long infragnathal with a prominent anterior cusp, found in the Frasnian portion of the Genesee Group of New York, and originally described as "Dinichthys newberryi".
D. amblyodoratus is known from some fragmentary remains from Late Devonian strata of Kettle Point, Canada. The species name means "blunt spear" and refers to the way the nuchal and paranuchal plates in the back of the head form the shape of a blunted spearhead. Although it is known only from fragments, it is estimated to have been about 6 metres (19.7 ft) long in life.
D. raveri is a small, possibly 1-m-long species known from an uncrushed skull roof, found in a carbonate concretion from near the bottom of the Huron Shale, of the Famennian Ohio Shale strata. Besides its small size, it had comparatively large eyes. Because D. raveri was found in the strata directly below the strata where the remains of D. terrelli are found, D. raveri may have given rise to D. terrelli. The species name commemorates Clarence Raver of Wakeman, Ohio, who discovered the concretion where the holotype was found.
The largest species, D. terrelli, is estimated to have grown up to 6 m (19.7 ft) in length and 1 t (1.1 short tons) in weight, making it one of the largest placoderms to have existed. Like other placoderms, Dunkleosteus had a two-part bony, armoured exterior, which may have made it a relatively slow but powerful swimmer. Instead of teeth, Dunkleosteus possessed two pairs of sharp bony plates which formed a beak-like structure. Dunkleosteus, together with most other placoderms, may have also been among the first vertebrates to internalize egg fertilization, as seen in some modern sharks.
Mainly the armoured frontal sections of specimens have been fossilized, and consequently the appearance of the other portions of the fish is mostly unknown. Because of this, many reconstructions of the hindquarters are often based on smaller arthrodires, such as Coccosteus, which had preserved hind sections. However, an exceptionally preserved specimen of D. terrelli preserves ceratotrichia in a pectoral fin, implying that the fin morphology of placoderms was much more morphologically variable than previously thought, and was heavily influenced by locomotion requirements. This knowledge, coupled with the knowledge that fish morphology is more heavily influenced by feeding niche than phylogeny, allowed a 2017 study to infer the body shape of D. terrelli. This new reconstruction gives D. terrelli a much more shark-like profile, including a strong anterior lobe on its tail, in contrast to reconstructions based on other placoderms.
The most famous specimens of Dunkleosteus are displayed at the Cleveland Museum of Natural History, and others are displayed at the American Museum of Natural History, National Museum of Natural History, State Museum of Pennsylvania, Harrisburg and in the Queensland Museum in Brisbane, Queensland.
Dunkleosteus terrelli possessed a four-bar linkage mechanism for jaw opening that incorporated connections between the skull, the thoracic shield, the lower jaw and the jaw muscles joined together by movable joints. This mechanism allowed D. terrelli to both achieve a high speed of jaw opening, opening their jaws in 20 milliseconds and completing the whole process in 50–60 milliseconds (comparable to modern fishes that use suction feeding to assist in prey capture;) and producing high bite forces when closing the jaw, estimated at 6,000 N (612 kgf; 1,349 lbf) at the tip and 7,400 N (755 kgf; 1,664 lbf) at the blade edge in the largest individuals. The pressures generated in those regions were high enough to puncture or cut through cuticle or dermal armor suggesting that D. terrelli was adapted to prey on free-swimming, armored prey such as ammonites and other placoderms. Fossils of Dunkleosteus are frequently found with boluses of fish bones, semidigested and partially eaten remains of other fish. As a result, the fossil record indicates it may have routinely regurgitated prey bones rather than digest them. It probably inhabited inshore waters.
Morphological studies on the lower jaws of juveniles of D. terrelli reveal they were proportionally as robust as those of adults, indicating they already had the ability to produce high bite forces and likely were able to shear into resistant prey tissue similar to adults, albeit on a smaller scale. This pattern is in direct contrast to the condition common in tetrapods in which the jaws of juveniles are more gracile than in adults.
Arthrodira is an order of extinct armoured, 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.
Greek for "jointed neck", the arthrodires had movable joint between armor surrounding the head and body. Lacking distinct teeth, like all placoderms, they used the sharpened edges of a bony plate as a biting surface. The eye sockets are protected by a bony ring, a feature shared by birds and some ichthyosaurs. Early arthrodires, such as the genus Arctolepis, were well-armoured fishes with flattened bodies. The largest member of this group, Dunkleosteus, was a true superpredator of the latest Devonian period, reaching 1 to as much as 6 m in length. In contrast, the long-nosed Rolfosteus measured just 15 cm.
A common misconception is the arthrodires (along with all other placoderms) were sluggish bottom-dwellers that were outcompeted by more advanced fish. Leading to this misconception is that the arthrodire body plan remained relatively conserved (that is, the majority of arthrodires were bullet- or torpedo-shaped) during the Devonian period, save for increasing in size. However, during their reign, the arthrodires were one of the most diverse and numerically successful, if not the most successful, vertebrate orders of the Devonian, occupying a vast spectrum of roles from apex predator to detritus-nibbling bottom dweller. Despite their success, the arthrodires were one of many groups eliminated by the environmental catastrophes of the Late Devonian extinction, allowing other fish such as sharks to diversify into the vacated ecological niches during the Carboniferous period.Aspinothoracidi
Aspinothoracidi is a clade of placoderms, extinct armored fish most diverse during the Devonian. The gigantic apex predator Dinichthys, is the best-known member of this group. Many other genera, such as the infamous Dunkleosteus, were previously thought to be close relatives of Dinichthys and were grouped together in the family Dinichthyidae, though more recent studies have restricted that family to only its type species.Brachythoraci
Brachythoraci is an extinct suborder of arthrodire placoderms, armored fish most diverse during the Devonian. The suborder previously only contained the infraorder Coccosteina, but the more basal family, Heterosteidae is now placed within there too.Coccosteus
Coccosteus ("seed bone") is an extinct genus of arthrodire placoderm. 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. The largest specimens were about 40 centimetres (16 in), although the average length was 20 to 24 centimetres (7.9 to 9.4 in).
Like all other arthrodires, Coccosteus had a joint between the armour of the body and skull. In addition, it also had an internal joint between its neck vertebrae and the back of the skull, allowing for the mouth to be opened even wider. Along with the longer jaws, this allowed Coccosteus to feed on fairly large prey. The up-and-down movement of the skull also allowed for more water to be pumped through the gills. Possibly, the creature supplemented its diet with organic material filtered from mud using the gills. As with all other arthrodires, Coccosteus had bony dental plates embedded in its jaws, forming a beak. The beak was kept sharp by having the edges of the dental plates grind away at each other. Overall the creature looked similar to its gigantic cousin Dunkleosteus, save that its eyes were closer to the end of its snout than in its larger relative.Dinichthys
Dinichthys herzeri is an extinct, giant, marine arthrodire placoderm from the Late Devonian (Famennian stage) of Ohio and Tennessee. It was comparable in size, shape, and ecological role to the better-known Dunkleosteus. Originally described in 1868 by John Newberry on the basis of an incomplete skull roof and mandibles (AMNH 81), this species remains imperfectly known to this day.
For much of the 20th century, many unrelated large arthrodires were classified together within this genus, including species now assigned to Dunkleosteus, Eastmanosteus, and Titanichthys. Today, Dinichthys is considered a monotypic genus, containing only the type species, D. herzeri. Similarly, in a 2010 analysis, the family Dinichthyidae that once held a wide range of arthrodire genera was redefined as comprising only Dinichthys.The type species of Dunkleosteus was originally described as Dinichthys terrelli by Newberry in 1873. After complete exoskeletons of this species were discovered in the early 20th century, Din. terrelli served as the basis for life reconstructions of the genus as opposed to the fragmentary Din. herzeri, even long after terrelli was separated into Dunkleosteus by Jean Pierre Lehman in 1956. As a result, most illustrations captioned as Dinichthys are actually pictures of Dunkleosteus.Dunkleosteidae
Dunkleosteidae is an extinct family of arthrodire placoderms. The gigantic apex predator Dunkleosteus terrelli is the best known member of this group. While they were previously thought to be close relatives of the genus Dinichthys (when they were not synonymized as each other) and grouped together in the family Dinichthyidae, more recent studies have shown that the two taxa represent two very distinct clades within Arthrodira. The reappraisal of Kiangyousteus lead to a restructuring of the family, with the inclusions of the benthic, aberrant Heterosteus (and the other members of Heterosteidae) as the sister taxon of Dunkleosteus, and the Late Emsian Xiangshuiosteus as the sister taxon of Eastmanosteus calliaspis (with the direct implication that E. calliaspis does not belong in Eastmaneosteus), and the removal of Westralichthys from the family (now thought to be the most basal member of the superfamily Dunkleosteoidea, and sister taxon of Panxiosteidae and Dunkleosteidae)Eastmanosteus
Eastmanosteus ("Eastman's bone") is a fossil genus of dunkleosteid placoderms. It was closely related to the giant Dunkleosteus, but differed from that genus in size, in possessing a distinctive tuberculated bone ornament, a differently shaped nuchal plate and a more zig-zagging course of the sutures of the skull roof.Species of Eastmanosteus had powerful jaws with sharp cutting edges and were likely active predators. Fossils have been found in many parts of the world in marine sediments dating from the Middle to Late Devonian. They were medium-to-large fish, with specimens E. pustulosus and E. licharevi approaching a total length of 3 metres. Complete exoskeletons with soft-tissue traces of E. calliaspis from Australia make this one of the best known dunkleosteids.Fish jaw
Most bony fishes have two sets of jaws made mainly of bone. The primary oral jaws open and close the mouth, and a second set of pharyngeal jaws are positioned at the back of the throat. The oral jaws are used to capture and manipulate prey by biting and crushing. The pharyngeal jaws, so-called because they are positioned within the pharynx, are used to further process the food and move it from the mouth to the stomach.Cartilaginous fishes, such as sharks and rays, have one set of oral jaws made mainly of cartilage. They do not have pharyngeal jaws. Generally jaws are articulated and oppose vertically, comprising an upper jaw and a lower jaw and can bear numerous ordered teeth. Cartilaginous fishes grow multiple sets (polyphyodont) and replace teeth as they wear by moving new teeth laterally from the medial jaw surface in a conveyor-belt fashion. Teeth are replaced multiple times also in most bony fishes, but unlike cartilaginous fishes, the new tooth erupts only after the old one has fallen out.
Jaws probably originated in the pharyngeal arches supporting the gills of jawless fish. The earliest jaws appeared is now extinct placoderms and spiny sharks during the Silurian, about 430 million years ago. The original selective advantage offered by the jaw was probably not related to feeding, but to increased respiration efficiency—the jaws were used in the buccal pump to pump water across the gills. The familiar use of jaws for feeding would then have developed as a secondary function before becoming the primary function in many vertebrates. All vertebrate jaws, including the human jaw, evolved from early fish jaws. The appearance of the early vertebrate jaw has been described as "perhaps the most profound and radical evolutionary step in the vertebrate history". Fish without jaws had more difficulty surviving than fish with jaws, and most jawless fish became extinct.
Jaws use linkage mechanisms. These linkages can be especially common and complex in the head of bony fishes, such as wrasses, which have evolved many specialized feeding mechanisms. Especially advanced are the linkage mechanisms of jaw protrusion. For suction feeding a system of linked four-bar linkages is responsible for the coordinated opening of the mouth and the three-dimensional expansion of the buccal cavity. Other linkages are responsible for protrusion of the premaxilla. Linkage systems are widely distributed in animals. The most thorough overview of the different types of linkages in animals has been provided by M. Muller, who also designed a new classification system, which is especially well suited for biological systems.Gorgonichthys
Gorgonichthys clarki is an extinct arthrodire placoderm of the superfamily Dinichthyloidea. Fossils of G. clarki are found in the Upper Famennian Cleveland Shales of Late Devonian Ohio. G. clarki is estimated to have reached 6 meters in length. However it still may not have been as heavily built as its contemporary Dunkleosteus.Hadrosteidae
Hadrosteidae is a family of arthrodire placoderms from the Late Devonian. It was originally erected for the late Frasnian Hadrosteus, from the Kellwasserkalk facies. Later, the family was subjectively subsumed into Dinichthyidae due to Hadrosteus' anatomical similarities with Dunkleosteus and Dinichthys. In 1967, Obruchev placed the enigmatic arthrodire incertae sedis Diplognathus, from the Eastern American Famennian, within Hadrosteidae, on the basis of how the two genera have similar denticle ("teeth") patterns of the inferognathals, though, Denison (1978) contests this placement. With the redefining of Dinichthyidae as a monotypic family for Dinichthys, and only a few other genera placed within Dunkleosteidae, Hadrosteidae is now seen as a valid family again.Harrytoombsia
The placoderm genus Harrytoombsia was a fast-swimming predator.
It had knife-like blades, covered with tissue similar to enamel, on the outer edge of the jaw.
Harrytoombsia was the ‘little brother’ of the five-metre-long placoderm Dunkleosteus, the giant shark-like fish of its time, which preyed on its smaller relatives.Hungry Shark
Hungry Shark is a series of arcade-style RPG games developed and published by Future Games of London (prior to Hungry Shark Evolution) and Ubisoft (since Hungry Shark Evolution). The games allow players to control several unique species of sharks, including mako sharks, great white sharks, hammerhead sharks, reef sharks, and megalodon. To progress, the player must consume other marine animals and grow in size until the next, more powerful shark is available for purchase. In May 2016, Hungry Shark World was downloaded 10 million times in six days, reaching the top 10 free iPhone and Android apps.List of placoderm genera
This list of placoderms is an attempt to create a comprehensive listing of all genera from the fossil record that have ever been considered to be members of the class Placodermi. This list excludes purely vernacular terms. It includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomina dubia), or were not formally published (nomina nuda), as well as junior synonyms of more established names, and genera that are no longer considered placoderms.
This list includes 334 generic names.List of the prehistoric life of Ohio
This list of the prehistoric life of Ohio contains the various prehistoric life-forms whose fossilized remains have been reported from within the US state of Ohio.Placodermi
Placodermi (from the Greek πλάξ = plate and δέρμα = skin, literally "plate-skinned") 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. Placoderms are paraphyletic, and consist of several distinct outgroups or sister taxa to all living jawed vertebrates, which originated among their ranks. This is illustrated by a 419-million-year-old fossil, Entelognathus, from China, which is the only known placoderm with a type of bony jaw like that found in modern bony fishes. This includes a dentary bone, which is found in humans and other tetrapods. The jaws in other placoderms were simplified and consisted of a single bone. Placoderms were also the first fish to develop pelvic fins, the precursor to hindlimbs in tetrapods, as well as true teeth. Paraphyletic groupings are problematic, as one can not talk precisely about their phylogenic relationships, their characteristic traits and literal extinction. 380-million-year-old fossils of three other genera, Incisoscutum, Materpiscis and Austroptyctodus, represent the oldest known examples of live birth.The first identifiable placoderms appear in the fossil record during the late Llandovery epoch of the early Silurian. The various groups of placoderms were diverse and abundant during the Devonian, but became extinct at the end-Devonian Hangenberg event 358.9 million years agoRolfosteus
Rolfosteus canningensis is an extinct arthrodire placoderm from the Late Devonian of the Gogo Formation of Western Australia.
The 15 centimetres (5.9 in) long creature had tough plating on the front of its body. Like other arthrodires such as Coccosteus and the giant Dunkleosteus it had sharp, bony plates in its mouth which formed a turtle-like beak for cutting prey to pieces. Rolfosteus's most unusual feature was its highly elongated snout, which may have been used to enhance its sense of smell, as well as increase its hydrodynamic streamlining.Sea Monsters (TV series)
Sea Monsters is a 2003 BBC television trilogy which used computer-generated imagery to show past life in Earth's seas. In the U.S. it was known as Chased by Sea Monsters. It was made by Impossible Pictures, the creators of Walking with Dinosaurs, Walking with Beasts and Walking with Monsters. In the series, the British wildlife presenter Nigel Marven is shown traveling to seven past seas in the history of the Earth and scuba diving there, in order of dangerousness with the most dangerous last. He travels in a white sailboat or motorboat roughly 24 m (80 ft) long named 'The Ancient Mariner'. His time travelling device is not mentioned or shown, and the closest thing to it is his time map, showing the timeline of the seven deadliest seas and the creatures that lived at the time. He uses a scuba set with a fullface mask so he can talk underwater to produce the commentary. He performs some dives using a strong shark cage, which is spherical to make it harder for large sea creatures to bite it.Timeline of Devonian research
This timeline of Devonian research is a chronological listing of events in the history of geology and paleontology focused on the study of earth during the span of time lasting from 419.2–358.9 million years ago and the legacies of this period in the rock and fossil records.Titanichthys
Titanichthys is a 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 Titanichys 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.