Dunkleosteus Raveri
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''Dunkleosteus'' is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of large
arthrodire Arthrodira (Greek for "jointed neck") is an Order (biology), 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 penetratin ...
("jointed-neck") fish that existed during the
Late Devonian 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 million years ago ( Ma), to the beginning of the succeeding ...
period, about 382–358
million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...
. It was a
pelagic fish Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs. ...
inhabiting open waters, and one of the first vertebrate
apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...
s of any
ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...
. ''Dunkleosteus'' consists of ten species, some of which are among the largest
placoderm Placoderms (from Ancient Greek πλάξ 'plax'', ''plakos'''Plate (animal anatomy), plate' and δέρμα 'derma'''skin') are vertebrate animals of the class (biology), class Placodermi, an extinct group of prehistoric fish known from Pal ...
s ("plate-skinned") to have ever lived: ''D. terrelli'', ''D. belgicus'', ''D. denisoni'', ''D. marsaisi'', ''D. magnificus'', ''D. missouriensis'', ''D. newberryi'', ''D. amblyodoratus'', ''D. raveri'', and ''D. tuderensis.'' However, the validity of several of these species is unclear. The largest and best known species is ''D. terrelli''. Since body shape is not known, various methods of estimation put the living total length of the largest known specimen of ''D. terrelli'' between long and its weight around . Lengths of or more are poorly supported, with the most recent and extensive studies on the body shape and size of ''D. terrelli'' producing estimated lengths of approximately for typical adults and for exceptionally large individuals of this species. ''Dunkleosteus'' could quickly open and close its jaw, creating suction like modern-day suction feeders, and had a bite force that is considered the highest of any living or fossil fish, and among the highest of any animal.
Fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
of ''Dunkleosteus'' have been found in the United States, Canada, Poland, Belgium, and Morocco.


Discovery

''Dunkleosteus'' fossils were first discovered in 1867 by Jay Terrell, a hotel owner and amateur
paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...
who collected fossils in the cliffs along
Lake Erie Lake Erie ( ) is the fourth-largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and also has the shortest avera ...
near his home of Sheffield Lake, Ohio (due west of
Cleveland Cleveland is a city in the U.S. state of Ohio and the county seat of Cuyahoga County. Located along the southern shore of Lake Erie, it is situated across the Canada–U.S. maritime border and approximately west of the Ohio-Pennsylvania st ...
), United States. Terrell donated his fossils to
John Strong Newberry John Strong Newberry (December 22, 1822 – December 7, 1892) was an American physician, geologist and paleontologist. He participated as a naturalist and surgeon on three expeditions to explore and survey the western United States. During the C ...
and the Ohio Geological Survey, who in 1873 described all the material as belonging to a single new
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
and
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
: ''
Dinichthys herzeri ''Dinichthys'' (from , 'terrible' and 'fish') is an extinct monospecific genus of large marine arthrodire placoderm from the Late Devonian (Famennian stage) measuring around long. Fossils were recovered from the Ohio Shale Formation along ...
''. However, with later fossil discoveries, by 1875 it became apparent multiple large fish species were present in the
Ohio Shale The Ohio Shale is a geologic formation in Ohio. It preserves fossils dating back to the Devonian period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" ...
. ''
Dinichthys herzeri ''Dinichthys'' (from , 'terrible' and 'fish') is an extinct monospecific genus of large marine arthrodire placoderm from the Late Devonian (Famennian stage) measuring around long. Fossils were recovered from the Ohio Shale Formation along ...
'' came from the lowermost layer, the
Huron Shale Huron may refer to: Native American ethnography * Huron people, who have been called Wyandotte, Wyandot, Wendat and Quendat * Huron language, an Iroquoian language * Huron-Wendat Nation, or Huron-Wendat First Nation, or Nation Huronne-Wendat * N ...
, whereas most of the fossils were coming from the younger
Cleveland Shale The Cleveland Shale, also referred to as the Cleveland Member of the Ohio Shale, is a Late Devonian (Famennian) shale Member (geology), geologic member in the eastern United States. Identification and name The Cleveland Shale was identified in ...
and represented a distinct species. Newberry named this more common species "''Dinichthys''" ''terrelli'', after Terrell. Most of Terrell's original collection does not survive, having been destroyed by a fire in Elyria, Ohio, in 1873. The largest collection of ''Dunkleosteus'' fossils in the world is housed at the
Cleveland Museum of Natural History The Cleveland Museum of Natural History is a natural history museum in University Circle, a district of educational, cultural and medical institutions approximately five miles (8 km) east of Downtown Cleveland, Ohio, United States. The ...
, with smaller collections (in descending order of size) held at the
American Museum of Natural History The American Museum of Natural History (AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. Located in Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 21 interconn ...
,
Smithsonian National Museum of Natural History The National Museum of Natural History (NMNH) is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. With ...
,
Yale Peabody Museum The Peabody Museum of Natural History at Yale University (also known as the Yale Peabody Museum of Natural History or the Yale Peabody Museum) is one of the oldest, largest, and most prolific university natural history museums in the world. It ...
, the
Natural History Museum in London The Natural History Museum in London is a museum that exhibits a vast range of specimens from various segments of natural history. It is one of three major museums on Exhibition Road in South Kensington, the others being the Science Museum and ...
, and the
Cincinnati Museum Center The Cincinnati Museum Center is a museum complex operating out of the Cincinnati Union Terminal in the Queensgate neighborhood of Cincinnati, Ohio. It houses museums, theater, a library, and a symphonic pipe organ, as well as special travelin ...
. Specimens of ''Dunkleosteus'' are on display in many museums throughout the world (see table below), most of which are casts of the same specimen: CMNH 5768, the largest well-preserved individual of ''D. terrelli''. The original CMNH 5768 is on display in the Cleveland Museum of Natural History.


Taxonomy

''Dunkleosteus'' was named by
Jean-Pierre Lehman Jean-Pierre Lehman (10 August 1914 – 26 February 1981) was a French paleontologist who specialized on tetrapods and actinopterygians. He followed early ideas comparative anatomy to study evolution through cladistic ideas and making use of bio ...
in 1956 to honour David Dunkle (1911–1984), former curator of
vertebrate paleontology Vertebrate paleontology is the subfield of paleontology that seeks to discover, through the study of fossilized remains, the behavior, reproduction and appearance of extinct vertebrates (animals with vertebrae and their descendants). It also t ...
at the Cleveland Museum of Natural History. The genus name ''Dunkleosteus'' combines David Dunkle's surname with the Greek word ( 'bone'), literally meaning "Dunkle's bone". Originally thought to be a member of the genus ''
Dinichthys ''Dinichthys'' (from , 'terrible' and 'fish') is an extinct monospecific genus of large marine arthrodire placoderm from the Late Devonian (Famennian stage) measuring around long. Fossils were recovered from the Ohio Shale Formation along ...
'', ''Dunkleosteus'' was later recognized as belonging to its own genus in 1956. It was thought to be closely related to ''Dinichthys'', and they were grouped together in the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Dinichthyidae ''Dinichthys'' (from , 'terrible' and 'fish') is an extinct monospecific genus of large marine arthrodire placoderm from the Late Devonian (Famennian stage) measuring around long. Fossils were recovered from the Ohio Shale Formation along ...
. However, in the
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
analysis of Carr and Hlavin (2010), ''Dunkleosteus'' and ''Dinichthys'' were found to belong to separate
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
s of arthrodires: ''Dunkleosteus'' belonged to a group called the
Dunkleosteoidea Dunkleosteoidea is an extinct superfamily of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator ''Dunkleosteus terrelli'' is the best known member of this group. Phylogeny Eubrachythoraci is divided into the ...
while ''
Dinichthys ''Dinichthys'' (from , 'terrible' and 'fish') is an extinct monospecific genus of large marine arthrodire placoderm from the Late Devonian (Famennian stage) measuring around long. Fossils were recovered from the Ohio Shale Formation along ...
'' belonged to the distantly related
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 pre ...
. Carr & Hlavin resurrected the family
Dunkleosteidae Dunkleosteidae is an extinct family (biology), family of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator ''Dunkleosteus terrelli'' is the best known member of this group. Phylogeny While members of Dunkleo ...
and placed ''Dunkleosteus'', ''
Eastmanosteus ''Eastmanosteus'' ("Eastman's bone") is a fossil genus of Dunkleosteidae, dunkleosteid placoderms. It was closely related to the giant ''Dunkleosteus'', but differed from that genus in size, in possessing a distinctive tuberculated bone ornament, ...
'', and a few other genera from Dinichthyidae within it. Dinichthyidae, in turn, is left a
monospecific In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...
family, though closely related to arthrodires like '' Gorgonichthys'' and '' Heintzichthys''. The
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
below from the study of Zhu & Zhu (2013) shows the placement of ''Dunkleosteus'' within
Dunkleosteidae Dunkleosteidae is an extinct family (biology), family of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator ''Dunkleosteus terrelli'' is the best known member of this group. Phylogeny While members of Dunkleo ...
and ''
Dinichthys ''Dinichthys'' (from , 'terrible' and 'fish') is an extinct monospecific genus of large marine arthrodire placoderm from the Late Devonian (Famennian stage) measuring around long. Fossils were recovered from the Ohio Shale Formation along ...
'' within the separate clade
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 pre ...
: Alternatively, the subsequent 2016 Zhu ''et al.'' study using a larger morphological dataset recovered
Panxiosteidae Panxiosteidae is an extinct family of arthrodire placoderms that lived during the Devonian period. Phylogeny The family Panxiosteidae was erected by Wang in 1979. Members of the family are noted for showing morphologically intermediate traits b ...
well outside of
Dunkleosteoidea Dunkleosteoidea is an extinct superfamily of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator ''Dunkleosteus terrelli'' is the best known member of this group. Phylogeny Eubrachythoraci is divided into the ...
, leaving the status of
Dunkleosteidae Dunkleosteidae is an extinct family (biology), family of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator ''Dunkleosteus terrelli'' is the best known member of this group. Phylogeny While members of Dunkleo ...
as a clade grouping separate from Dunkleosteoidea in doubt, as shown in the cladogram below:


Species

At least ten different species of ''Dunkleosteus'' have been described so far. However, many of them are poorly characterized and may be
synonyms A synonym is a word, morpheme, or phrase that means precisely or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are a ...
of previously named species or not pertain to ''Dunkleosteus''. ''Dunkleosteus'' as currently defined is a
wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by e ...
for large dunkleosteoid
arthrodires Arthrodira (Greek for "jointed neck") 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 eco ...
that are more evolutionarily derived than ''
Eastmanosteus ''Eastmanosteus'' ("Eastman's bone") is a fossil genus of Dunkleosteidae, dunkleosteid placoderms. It was closely related to the giant ''Dunkleosteus'', but differed from that genus in size, in possessing a distinctive tuberculated bone ornament, ...
''. The
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
, ''D. terrelli'', is the largest, best-known species of the genus. Size estimates for this species range from in length, though estimates greater than 4.5 m are poorly supported. Skulls of this species can be up to in length. ''D. terrelli'' fossil remains are found in Upper Frasnian to Upper Famennian Late Devonian strata of the United States (
Huron Huron may refer to: Native American ethnography * Huron people, who have been called Wyandotte, Wyandot, Wendat and Quendat * Huron language, an Iroquoian language * Huron-Wendat Nation, or Huron-Wendat First Nation, or Nation Huronne-Wendat * N ...
,
Chagrin Chagrin may refer to: *Shagreen Shagreen is a type of rawhide consisting of rough untanned skin, historically from a horse's or onager's back, or from shark or ray. Etymology The word derives from the French ' and is related to Italia ...
, and
Cleveland Shale The Cleveland Shale, also referred to as the Cleveland Member of the Ohio Shale, is a Late Devonian (Famennian) shale Member (geology), geologic member in the eastern United States. Identification and name The Cleveland Shale was identified in ...
s of Ohio, the Conneaut and Chadakoin Formations of
Pennsylvania Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...
, the Chattanooga Shale of Tennessee, the
Lost Burro Formation The Lost Burro Formation is a Middle to Upper/Late Devonian geologic formation in the Mojave Desert of California in the Western United States. Geology The Dolomite formation is exposed in sections of the Darwin Hills, the Santa Rosa Hills, ...
of California, and possibly the Ives
breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...
of Texas) and
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
. ''D. belgicus'' (?) is known from fragments described from the
Famennian The Famennian is the later of two faunal stages in the Late Devonian epoch. The most recent estimate for its duration is that it lasted from around 371.1 to 359.3 million years ago. An earlier 2012 estimate, still used by the International Commis ...
of
Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...
. The median dorsal plate is characteristic of the genus, but, a plate that was described as a suborbital is an anterolateral. Lelièvre (1982) considers this
taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
a ''
nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...
'' ("doubtful name") and suggests the material may actually pertain to '' Ardennosteus''. ''D. denisoni'' is known from a small median dorsal plate, typical in appearance for ''Dunkleosteus'', but much smaller than normal. It is comparable in skull structure to ''D. marsaisi''. ''D. marsaisi'' refers to the ''Dunkleosteus'' fossils from the Lower Famennian Late Devonian strata of the
Atlas Mountains The Atlas Mountains are a mountain range in the Maghreb in North Africa. They separate the Sahara Desert from the Mediterranean Sea and the Atlantic Ocean; the name "Atlantic" is derived from the mountain range, which stretches around through M ...
in
Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...
. It differs in size, the known skulls averaging a length of 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 ''Eastmanosteus'' ("Eastman's bone") is a fossil genus of Dunkleosteidae, dunkleosteid placoderms. It was closely related to the giant ''Dunkleosteus'', but differed from that genus in size, in possessing a distinctive tuberculated bone ornament, ...
''. ''D. magnificus'' is a large placoderm from the Frasnian Rhinestreet Shale of New York. It was originally described as ''
Dinichthys ''Dinichthys'' (from , 'terrible' and 'fish') is an extinct monospecific genus of large marine arthrodire placoderm from the Late Devonian (Famennian stage) measuring around long. Fossils were recovered from the Ohio Shale Formation along ...
magnificus'' by Hussakof and Bryant in 1919, then as "''Dinichthys mirabilis''" by Heintz in 1932. Dunkle and Lane (1971) moved it to ''Dunkleosteus'', whereas Dennis-Bryan (1987) considered it to belong to the genus ''
Eastmanosteus ''Eastmanosteus'' ("Eastman's bone") is a fossil genus of Dunkleosteidae, dunkleosteid placoderms. It was closely related to the giant ''Dunkleosteus'', but differed from that genus in size, in possessing a distinctive tuberculated bone ornament, ...
''. This species has a skull length of and a total estimated length of approximately . ''D. missouriensis'' is known from fragments from Frasnian
Missouri Missouri (''see #Etymology and pronunciation, pronunciation'') is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it border ...
. Dunkle and Lane regard them as being very similar to ''D. terrelli''. In his revision of ''Dunkleosteus'' taxonomy, Hlavin (1976) considers this species to be tentatively synonymous with ''D. terrelli'' (''Dunkleosteus'' cf. ''D. terrelli''). ''D. newberryi'' is known primarily from a long infragnathal with a prominent anterior cusp, found in the Frasnian portion of the
Genesee Group The Genesee Formation (Group) is a geologic formation in New York. It is equivalent the Harrell Shale in Pennsylvania. It dates back to the Upper Devonian period. It is the basal unit of the Frasnian and Upper Devonian period. The Genesee Forma ...
of New York, and originally described as ''Dinichthys newberryi''. Lebedev et al. (2023) noted ''D. newberryi'' has an unusually long marginal tooth row compared to other species of ''Dunkleosteus'' and lacks the accessory odontoids typical of this genus, suggesting it might not belong to ''Dunkleosteus'' or even Dunkleosteoidea. ''D. amblyodoratus'' is known from some fragmentary remains from Late Devonian strata of Kettle Point Formation, Ontario. The species name means 'blunt spear' and refers to the way the
nuchal The nape is the back of the neck. In technical anatomical/medical terminology, the nape is also called the nucha (from the Medieval Latin rendering of the Arabic , ). The corresponding adjective is ''nuchal'', as in the term ''nuchal rigidity' ...
and paranuchal plates in the back of the head form the shape of a blunted spearhead. ''D. raveri'' is a small species, possibly 1 meter long, known from an uncrushed skull roof found in a carbonate concretion from near the bottom of the Huron Shale, of the Famennian
Ohio Shale The Ohio Shale is a geologic formation in Ohio. It preserves fossils dating back to the Devonian period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" ...
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 Wakeman is a village (United States)#Ohio, village in Huron County, Ohio, Huron County, Ohio, United States, along the Vermilion River (Ohio), Vermilion River. Its namesake was Jesup Wakeman, an early settler of Fairfield County, Connecticut, Fa ...
, who discovered the concretion containing the
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
. ''D. tuderensis'' is known from an infragnathal found in the lower-middle
Famennian The Famennian is the later of two faunal stages in the Late Devonian epoch. The most recent estimate for its duration is that it lasted from around 371.1 to 359.3 million years ago. An earlier 2012 estimate, still used by the International Commis ...
-aged Bilovo Formation of the
Tver Region Tver Oblast (, ) is a federal subject of Russia (an oblast). Its administrative center is the city of Tver. From 1935 to 1990, it was known as Kalinin Oblast (). Population: Tver Oblast is a region of lakes, such as Seliger and Brosno. Much of ...
in northwest Russia. The specific name refers to the Maliy Tuder River as the holotype was found on its bank. In total, of the ten or so species listed above only four are agreed upon as valid species of ''Dunkleosteus'' by all researchers: ''D. terrelli'' (which may or may not include ''Dunkleosteus'' material from Morocco), ''D. raveri'', ''D. tuderensis'', and possibly ''D. amblyodoratus'' (which is known from limited material that appears distinct but is difficult to compare with other dunkleosteids). The taxonomy of early late
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
(
Frasnian The Frasnian is one of two faunal stages in the Late Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Givetian Stage and followed by the Famennian Stage. Major reef-building was under way during ...
) species is poorly established, whereas latest
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
(
Famennian The Famennian is the later of two faunal stages in the Late Devonian epoch. The most recent estimate for its duration is that it lasted from around 371.1 to 359.3 million years ago. An earlier 2012 estimate, still used by the International Commis ...
) species are easily referable to this genus. This is not counting additional material assigned to ''Dunkleosteus'' sp. from the
Famennian The Famennian is the later of two faunal stages in the Late Devonian epoch. The most recent estimate for its duration is that it lasted from around 371.1 to 359.3 million years ago. An earlier 2012 estimate, still used by the International Commis ...
of California, Texas, Tennessee, and Poland.


Description


Size and anatomy

''Dunkleosteus'' was covered in
dermal bone A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton, including much of the skull, jaws, gill covers, shoulder girdle, fin rays ( lepidotrich ...
forming armor plates across its skull and front half of its
trunk Trunk may refer to: Biology * Trunk (anatomy), synonym for torso * Trunk (botany), a tree's central superstructure, and the stem of woody plants * Trunk of corpus callosum, in neuroanatomy * Elephant trunk, the proboscis of an elephant Comput ...
. This armor is often described as being over thick, but this is only across the thickened nuchal plate at the back of the skull. Thickening of the nuchal plate is a common feature of eubrachythoracid
arthrodires Arthrodira (Greek for "jointed neck") 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 eco ...
. Across the rest of the body the armor is generally much thinner, only about in thickness. The plates of ''Dunkleosteus'' had both a hard cortical and a marrow-filled
cancellous A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...
layer, unlike most
teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...
fishes and more similar to
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
bones. Mainly the armored frontal sections of specimens have been
fossilized A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
, and consequently, the appearance of the other portions of the fish is mostly unknown. In fact, only about 5% of ''Dunkleosteus'' specimens have more than a quarter of their skeleton preserved. Because of this, many reconstructions of the hindquarters are often based on fossils of smaller
arthrodire Arthrodira (Greek for "jointed neck") is an Order (biology), 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 penetratin ...
s, such as ''
Coccosteus ''Coccosteus'' (from , 'berry' and 'bone') 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, th ...
'', which have preserved hind sections, leading to widely varying size estimates. ''Dunkleosteus terrelli'' is one of the largest known placoderms, with its maximum size being variably estimated as anywhere from by different researchers. However, most cited length estimates are speculative and lack quantitative or statistical backing, and lengths of or more are poorly supported. Most studies that estimate the length of ''Dunkleosteus terrelli'' do not provide information as to how these estimates were calculated, the measurements used to scale them, or which specimens were examined. Estimates in these studies are implied to be based on either CMNH 5768 (the largest complete armor of ''D. terrelli'') or CMNH 5936 (the largest known jaw fragment). Additionally, these reconstructions often require ''Dunkleosteus'' to lack many features consistent across the body plans of other arthrodires like ''
Coccosteus ''Coccosteus'' (from , 'berry' and 'bone') 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, th ...
'' and ''
Amazichthys ''Amazichthys'' is an Extinction, extinct genus of Selenosteidae, selenosteid Arthrodira, arthrodire from the Famennian, Middle Famennian of the Late Devonian of the Anti-Atlas, Anti-Atlas Mountains of Morocco. It contains a single species, ''Amaz ...
.'' The most extensive analyses of body size and shape in ''Dunkleosteus terrelli'' produce length estimates of ~ for typical adults of this species, with very rare and exceptional individuals potentially reaching lengths of . These estimates were calculated using several different size proxies (head length, orbit-opercular length ead length minus snout length ventral shield length, entering angle, locations of the pectoral and pelvic girdles relative to total length), which produce largely similar results. Statistical margins of error in these methods mean lengths as great as in typical adults and for exceptional individuals remain possible, but greater lengths result in proportions largely outside what is seen in other
arthrodires Arthrodira (Greek for "jointed neck") 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 eco ...
and jawed fishes more generally, especially in terms of the size of the head and trunk armor relative to the total length of the animal and the relative location of the
pectoral Pectoral may refer to: * The chest region and anything relating to it. * Pectoral cross, a cross worn on the chest * a decorative, usually jeweled version of a gorget * Pectoral (Ancient Egypt), a type of jewelry worn in ancient Egypt * Pectora ...
and
pelvic fins Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...
. Indeed, the implied proportions under the upper ranges of the margins of error suggest even those lengths may be overly generous. Lengths at the lower end of the margins of error are unlikely given the preserved lengths of the head and trunk armor. Most studies with well-defined methods produce lengths of or less for ''Dunkleosteus terrelli'', with the exception of Ferrón ''et al.'' (2017), which produces larger estimates of based on upper jaw perimeter of modern sharks. However, arthrodires have proportionally larger mouths than modern sharks, making the lengths estimated by Ferrón ''et al.'' (2017) unreliable. Upper jaw perimeter overestimates the size of complete arthrodires like ''
Coccosteus ''Coccosteus'' (from , 'berry' and 'bone') 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, th ...
'' and the estimates of Ferrón ''et al.'' (2017) result in ''Dunkleosteus'' having an extremely small head and hyper-elongate trunk relative to the known dimensions of the fossils. The reconstruction presented in Ferrón ''et al.'' (2017) is also incorrectly scaled to the known dimensions of the fossil material; if scaled to the size of CMNH 5768, it produces a length of , agreeing with the shorter estimates in later studies. Carr (2010) estimated a long adult individual of ''Dunkleosteus terrelli'' to have weighed , assuming a shark-like body plan and a similar length-weight relationship. Engelman (2023), using an
ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface;  that is, a Surface (mathemat ...
volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...
tric method, estimated weights of for typical ( long) adult ''Dunkleosteus'', and weights of for the largest ( in this study) individual. The higher weights by Engelman (2023) are mostly a result of the fact that arthrodires tend to have relatively deeper and wider bodies compared to sharks. An exceptionally preserved specimen of ''D. terrelli'' preserves a
pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...
outline with ceratotrichia, implying that the fin morphology of placoderms was much more variable than previously thought, and was heavily influenced by locomotory 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
caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...
shape of ''D. terrelli'', reconstructing this fin with a strong ventral lobe, a high
aspect ratio The aspect ratio of a geometry, geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side—the ratio of width to height, when the rectangl ...
, narrow
caudal peduncle Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...
, in contrast to previous reconstructions based on the
anguilliform Fish locomotion is the various types of animal locomotion used by fish, principally by aquatic locomotion, swimming. This is achieved in different groups of fish by a variety of mechanisms of propulsion, most often by wave-like lateral flexions ...
caudal fin of coccosteomorph placoderms. The only vertebral remains known for Dunkleosteus are a small series of 16 vertebrae within the trunk armor of the specimen CMNH 50322. Most of these vertebrae are highly fused, and have very prominent, laterally-projecting articular facets compared to other arthrodires. Although many arthrodires show the incorporation of anterior vertebrae into a synarcual, in these species the fused region is small whereas the fused region of ''Dunkleosteus'' extends almost to the end of the trunk armor, which would make its spine very stiff. This, along with a ridge on the inside of the trunk armor suggesting an unusually well-developed attachment for the horizontal septum, suggests ''Dunkleosteus'' may have had an anteriorly stiffened spine and specialized connective tissues to transmit force generated by the anterior trunk
muscles Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...
to the tail fin, similar to
thunniform Fish locomotion is the various types of animal locomotion used by fish, principally by swimming. This is achieved in different groups of fish by a variety of mechanisms of propulsion, most often by wave-like lateral flexions of the fish's body a ...
vertebrates like lamnids and tunas. The pelvic girdle of ''Dunkleosteus'' is relatively small relative to the overall size of the armor. Several specimens preserve associated pelvic girdles, but their original position was not recorded during preservation. However, because these specimens were excavated from cliff faces, they were probably found in close to the armor, suggesting these fins were associated with the end of the ventral shield as in other arthrodires. One specimen may preserve pelvic fin basals near the end of the trunk armor.


Length estimations of ''D. terrelli''


Paleobiology


Diet

''Dunkleosteus terrelli'' possessed a
four-bar linkage In the study of Mechanism (engineering), mechanisms, a four-bar linkage, also called a four-bar, is the simplest closed-Kinematic chain, chain movable linkage (mechanical), linkage. It consists of four Rigid body, bodies, called ''bars'' or ''link ...
mechanism for
jaw The jaws are a pair of opposable articulated structures at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth ...
opening that incorporated connections between the skull, the thoracic shield, the lower jaw and the jaw muscles joined 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 Aquatic feeding mechanisms face a special difficulty as compared to feeding on land, because the density of water is about the same as that of the prey, so the prey tends to be pushed away when the mouth is closed. This problem was first identifi ...
to assist in prey capture) and producing high bite forces when closing the jaw, estimated at at the tip and at the blade edge, or even up to and respectively. The bite force is considered the highest of any living or fossil fish, and among the highest of any animal. The pressures generated in those regions were high enough to puncture or cut through
cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...
or
dermal The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...
armor, suggesting that ''D. terrelli'' was adapted to prey on free-swimming, armored prey such as
ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...
s and other placoderms. In addition, teeth of a
chondrichthyan Chondrichthyes (; ) is a class (biology), class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which ...
thought to belong to ''
Orodus ''Orodus'' (from , 'beautiful' and 'tooth') is an extinct genus of orodontiform cartilaginous fish. Fossils are known from the late Devonian to Late Carboniferous of Europe, Asia and North America. Most species are only known from their rou ...
'' (''Orodus'' spp.) were found in association with ''Dunkleosteus'' remains, suggesting that these were probably stomach contents regurgitated from the animal. ''Orodus'' is thought to be tachypelagic, or a fast-swimming
pelagic fish Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs. ...
. Thus, ''Dunkleosteus'' might have been fast enough to catch these fast organisms, and not a slow swimmer like originally thought. Fossils of ''Dunkleosteus'' are frequently found with boluses of fish bones, semidigested and partially eaten remains of other fish. As a result, the
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
record indicates it may have routinely regurgitated prey bones rather than digest them. Mature individuals probably inhabited deep sea locations, like other placoderms, living in shallow waters during adolescence. A specimen of ''Dunkleosteus'' (CMNH 5302), and '' Titanichthys'' (CMNH 9889), show damage said to be puncture damage from the bony fangs of other ''Dunkleosteus''.


Reproduction

''Dunkleosteus'', together with most other placoderms, may have also been among the first
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
s to internalize egg fertilization, as seen in some modern sharks. Some other placoderms have been found with evidence that they may have been
viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...
, including what appears to have been an
umbilical cord In Placentalia, placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord i ...
.


Growth

Morphological studies on the lower jaws of juveniles of ''D. terrelli'' reveal they were proportionally as robust as those of adults, indicating they already could 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
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
s in which the jaws of juveniles are more
gracile Gracility is slenderness, the condition of being gracile, which means slender. It derives from the Latin adjective ''gracilis'' (masculine or feminine), or ''gracile'' ( neuter), which in either form means slender, and when transferred for examp ...
than in adults.


See also

*
List of placoderms This list of placoderms is an attempt to create a comprehensive listing of all Genus, genera from the Fossil, fossil record that have ever been considered to be members of the Class (biology), class Placodermi. This list excludes purely vernacula ...


References


Further reading

*


External links


''Introduction to the Placodermi: Extinct Armored Fishes with Jaws''. Waggoner, Ben (2000). Retrieved Aug 1, 2005

MSNBC: Prehistoric fish packed a mean bite

BBC: Ancient 'Jaws' had monster bite
{{Taxonbar, from=Q131039, from2=Q911597, from3=Q911599, from4=Q911605, from5=Q911606, from6=Q911611, from7=Q911612, from8=Q911616, from9=Q911618, from10=Q911593, from11=Q25357547 Dunkleosteidae Apex predators Placoderms of Africa Fossils of Morocco Placoderms of Europe Fossils of Belgium Placoderms of North America Fossils of Canada Paleontology in Missouri Paleontology in Pennsylvania Paleontology in Tennessee Late Devonian first appearances Late Devonian animals Famennian extinctions Fossil taxa described in 1873 Fossil taxa described in 1956 Taxa named by John Strong Newberry Symbols of Ohio