dinocephalian
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Dinocephalians (terrible heads) are a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
of large-bodied early
therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
s that flourished in the
Early Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...
and
Middle Permian The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...
between 279.5 and 260 million years ago (Ma), but became extinct during the
Capitanian mass extinction event The Capitanian mass extinction event, also known as the end-Guadalupian extinction event or the pre-Lopingian crisis was an extinction event that predated the end-Permian extinction event and occurred around 260 million years ago during a period ...
. Dinocephalians included
herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
,
carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...
, and
omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
forms. Many species had thickened skulls with many knobs and bony projections. Dinocephalians were the first non-mammalian therapsids to be scientifically described and their fossils are known from Russia, China, Brazil, South Africa, Zimbabwe, and Tanzania.


Description

Apart from the
Biarmosuchia Biarmosuchians are an extinct clade of non-mammalian synapsids from the Permian. They are the most basal group of the therapsids. All of them were moderately-sized, lightly-built carnivores, intermediate in form between basal sphenacodont " pelyc ...
ns, the dinocephalians are the least advanced therapsids, although still uniquely specialised in their own way. They retain a number of primitive characteristics (e.g. no
secondary palate The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates. In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medi ...
, small dentary) shared with their
pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is ...
ancestors, although they are also more advanced in possessing therapsid adaptations like the expansion of the ilium and more erect limbs. They include
carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...
,
herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
, and
omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
forms. Some were
semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semi aquatic animals include: * Ve ...
, others were fully terrestrial. They were among the largest animals of the
Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...
period; only the biggest
Caseidae Caseidae are an extinct family of basal synapsids that lived from the Late Carboniferous to Middle Permian between about 300 and 265 million years ago. Fossils of these animals come from the south-central part of the United States (Texas, Okla ...
and
Pareiasaur Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with scutes which covered large areas of the body. They first appeared in southern Pangea during the Middle Permi ...
idea reaching them in size.


Size

Dinocephalians were generally large. The biggest herbivores ('' Tapinocephalus'') and omnivores ('' Titanosuchus'') may have massed up to , and were some long, while the largest carnivores (such as ''
Titanophoneus ''Titanophoneus'' ("titanic murderer") is an extinct genus of carnivorous dinocephalian therapsid from the Middle Permian. It is classified within the family Anteosauridae. The type species is ''Titanophoneus potens''. Remains of ''Titanophoneus'' ...
'' and '' Anteosaurus'') were at least as long, with heavy skulls long, and overall masses of around a half-tonne.


Skull

All dinocephalians are distinguished by the interlocking incisor (front) teeth. Correlated features are the distinctly downturned facial region, a deep temporal region, and forwardly rotated suspensorium. Shearing contact between the upper and lower teeth (allowing food to be more easily sliced into small bits for digestion) is achieved through keeping a fixed quadrate and a hinge-like movement at the jaw articulation. The lower teeth are inclined forward, and occlusion is achieved by the interlocking of the incisors. The later dinocephalians improved on this system by developing heels on the lingual sides of the incisor teeth that met against one another to form a crushing surface when the jaws were shut. Most dinocephalians also developed pachyostosis of the bones in the skull, which seems to have been an adaptation for intra-specific behaviour (head-butting), perhaps for territory or a mate. In some types, such as ''
Estemmenosuchus ''Estemmenosuchus'' (meaning "crowned crocodile" in Greek) is an extinct genus of large, early omnivorous therapsid. It is believed and interpreted to have lived during the middle part of the Middle Permian around 267 million years ago. The two s ...
'' and ''
Styracocephalus ''Styracocephalus platyrhynchus'' ('spike head') is an extinct species of tapinocephalian therapsids that lived during the Guadalupian epoch. ''Styracocephalus''s head ornament meant that it could be recognised from a distance. The most striki ...
'', there are also horn-like structures, which evolved independently in each case.


Evolutionary history

The dinocephalians are an ancient group and their ancestry is not clear. It is assumed that they must have evolved during the earlier part of the Roadian, or possibly even the Kungurian epoch, but no trace has been found. These animals radiated at the expense of the dying
pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is ...
s, who dominated during the early part of the
Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...
and may have even gone extinct due to competition with therapsids, especially the short-lived but most dominant dinocephalians. Even the earliest members, the
estemmenosuchid Estemmenosuchidae is an extinct family of large, very early herbivorous therapsids that flourished during the Guadalupian period. They are distinguished by horn-like structures, probably for display or agonistic behavior. Apart from the best kno ...
s and early brithopodids of the Russian Ocher fauna, were already a diverse group of herbivores and carnivores. During the Wordian and early Capitanian, advanced dinocephalians radiated into a large number of herbivorous forms, representing a diverse
megafauna In terrestrial zoology, the megafauna (from Greek μέγας ''megas'' "large" and New Latin ''fauna'' "animal life") comprises the large or giant animals of an area, habitat, or geological period, extinct and/or extant. The most common thresho ...
. This is well known from the ''Tapinocephalus'' Assemblage Zone of the Southern African
Karoo The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe !Orakobab or Khoemana word ''ǃ’Aukarob'' "Hardveld") is a semi-desert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its ex ...
. At the height of their diversity (middle or late Capitanian age) all the dinocephalians suddenly died out, during the
Capitanian mass extinction event The Capitanian mass extinction event, also known as the end-Guadalupian extinction event or the pre-Lopingian crisis was an extinction event that predated the end-Permian extinction event and occurred around 260 million years ago during a period ...
. The reason for their extinction is not clear; although disease, sudden climatic change, or other factors of environmental stress may have brought about their end. They were replaced by much smaller
therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
s; herbivorous
Dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typic ...
ia and carnivorous
Biarmosuchia Biarmosuchians are an extinct clade of non-mammalian synapsids from the Permian. They are the most basal group of the therapsids. All of them were moderately-sized, lightly-built carnivores, intermediate in form between basal sphenacodont " pelyc ...
ns, Gorgonopsians and
Therocephalia Therocephalia is an extinct suborder of eutheriodont therapsids (mammals and their close relatives) from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of thei ...
ns.


Taxonomy

* Class
Synapsid Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...
a ** Order
Therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
a *** Suborder Dinocephalia **** ?'' Driveria'' **** ?'' Eccasaurus'' **** ?'' Mastersonia'' **** ?'' Pelosuchus'' **** ?'' Tappenosaurus'' **** Family
Estemmenosuchidae Estemmenosuchidae is an extinct family of large, very early herbivorous therapsids that flourished during the Guadalupian period. They are distinguished by horn-like structures, probably for display or agonistic behavior. Apart from the best kno ...
***** ''
Estemmenosuchus ''Estemmenosuchus'' (meaning "crowned crocodile" in Greek) is an extinct genus of large, early omnivorous therapsid. It is believed and interpreted to have lived during the middle part of the Middle Permian around 267 million years ago. The two s ...
'' ***** '' Molybdopygus'' *****?'' Parabradysaurus'' **** ?Family Phreatosuchidae ***** '' Phreatosaurus'' ***** '' Phreatosuchus'' **** ?Family Phthinosuchidae ***** '' Phthinosuchus'' **** ?Family Rhopalodontidae *****?'' Phthinosaurus'' *****''
Rhopalodon ''Rhopalodon'' is an extinct genus of therapsids from the Permian of Russia. It has been variously classified as a dinosaur, a dinocephalian, or another branch of Reptilia. ''Rhopalodon'' is notable for being among the first reptiles mention ...
'' **** Clade
Anteosauria Anteosaurs are a group of large, primitive carnivorous dinocephalian therapsids with large canines and incisors and short limbs, that are known from the Middle Permian of South Africa, Russia, China, and Brazil. Some grew very large, with skulls ...
***** Family
Anteosauridae Anteosauridae is an extinct family of large carnivorous dinocephalian therapsids that are known from the Middle Permian of Asia, Africa, and South America.These animals were by far the largest predators of the Permian period, with skulls reaching ...
***** Family
Brithopodidae ''Brithopus'' is an extinct genus of dinocephalian therapsids. It contains a single species, ''Brithopus priscus'', known from fragmentary remains found in the Copper Sandstones near Isheevo, Russia. Description ''Brithopus'' was fairly large, ...
***** Family Deuterosauridae **** Clade Tapinocephalia ***** ?'' Dimacrodon'' ***** Family ? Driveriidae ***** Family ? Mastersoniidae ***** Family Styracocephalidae ***** Family
Tapinocephalidae Tapinocephalidae was an advanced family of tapinocephalians. It is defined as the clade containing '' Ulemosaurus'', ''Tapinocaninus'', and the Tapinocephalinae. They are known from both Russia and South Africa. In all probability, the Tapinocep ...
***** Family Titanosuchidae


See also

*
Evolution of mammals The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked l ...
* List of Permian tetrapods


References


Further reading

* Carroll, R. L. (1988), ''Vertebrate Paleontology and Evolution'', WH Freeman & Co.


External links


Dinocephalia
at Palaeos
Dinocephalia
at Palaeocritti {{Taxonbar, from=Q131810 Taxa named by Harry Seeley Guadalupian first appearances Guadalupian extinctions