Estemmenosuchidae is an extinct

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 ...

of large, very early

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

therapsids that flourished during the

Guadalupian The Guadalupian is the second and middle Series (stratigraphy), series/Epoch (geology), 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 an ...

period. They are distinguished by horn-like structures, probably for

display Display may refer to: Technology * Display device, output device for presenting information, including: ** Electronic visual display, output device to present information for visual or tactile reception *** Cathode-ray tube (CRT), that uses an el ...

agonistic behavior Agonistic behaviour is any social behaviour related to fighting, which can include aggressive behaviour, but also threats, displays, retreats, placation, and conciliation. The term "agonistic behaviour" was first defined and used by J.P. Scott ...

. Apart from the best known genus, ''

Estemmenosuchus ''Estemmenosuchus'' (meaning "crowned crocodile" in Greek language, Greek) is an extinct genus of large, early omnivore, omnivorous therapsid. It is believed and interpreted to have lived during the middle part of the Middle Permian around 267 m ...

'', the group is poorly known. To date, their fossils are known only from the

Perm Perm or PERM may refer to: Places * Perm, Russia, a city in Russia **Permsky District, the district **Perm Krai, a federal subject of Russia since 2005 **Perm Oblast, a former federal subject of Russia 1938–2005 ** Perm Governorate, an administr ...

region of Russia (a region referred to by Russian paleontologists as the Cis-Urals).

Description

Estemmenosuchids are among the most distinctive of the

Permian tetrapods Permian tetrapods were amphibians and reptiles that lived during the Permian Period. During this time, amphibians remained common, including various Temnospondyli and Lepospondyli. Synapsids became the dominant type of animal, represented by the ...

. The high and massive skull is equipped with a number of horns projecting both upwards and outwards, which were probably used for intra-specific display. The

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s and

canine teeth In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, eye teeth, vampire teeth, or fangs, are the relatively long, pointed teeth. In the context of the upper jaw, they are also known as '' fangs''. They can appear more fl ...

are large, but those at the side are reduced, with a serrated apex, and may have helped to break up plant material, although they were too small to be of much use. The body is large and bulky, indicating a large digestive tract for digesting volumes of plant food. The skull superficially resembles that of ''

Styracocephalus ''Styracocephalus platyrhynchus'' (Greek for "spiked-head") is an extinct genus of dinocephalian therapsid that existed during the mid-Permian throughout South Africa, but mainly in the Karoo Basin. It is often referred to by its single known sp ...

'', but the "horns" are formed from different bones.

Evolutionary relationships

Estemmenosuchids belong to the

Dinocephalia Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. ...

n group, a group of early, primitive, but diverse therapsids – often of large size – that are known only from the Middle Permian period. They are however far more primitive and unspecialised than the better known dinocephalians of the South African

Karoo The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe Khoemana (also known as !Orakobab or Korana) word is a semidesert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its extent is ...

(

Beaufort Group The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably under ...

), and mostly lived somewhat earlier. They are also unusual in that, despite their primitive nature and early date of appearance, they show herbivorous adaptations. Because of this, there have been two main interpretations of their evolutionary relationships with other Dinocephalia.

Hopson Hopson is a surname. Notable people with the name Hopson include: *Briggs Hopson (born 1965), Republican member of the Mississippi Senate *Dennis Hopson (born 1965), American basketball player and coach *Eben Hopson (1922–1980), Alaskan Native Am ...

and Barghusen in 1986, who provided the first

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

study of the Therapsida, coined the term

Tapinocephalia The Tapinocephalia are one of the major groups of dinocephalian therapsids and the major herbivorous group. Tapinocephalia has been found to consist of three clades: Styracocephalidae, Titanosuchidae, and the very successful Tapinocephalidae. ...

for herbivorous dinocephalians, as opposed to the "

Anteosaur 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 ...

ia" for the carnivorous forms. They suggested that Estemmenosuchids are very early/primitive members of the

. However

Thomas Kemp Thomas Kemp may refer to: *Thomas Read Kemp (1783–1844), English property developer and politician *Thomas Webster Kemp (1866–1928), Royal Navy admiral *Thomas Kemp of the Kemp baronets *Thomas Kemp (shipbuilder) *Tom Kemp (1921–1993), Marxi ...

(1982) and

Gillian King Gillian may refer to: Places * Gillian Settlement, Arkansas, an unincorporated community People Gillian (variant Jillian) is an English feminine given name, frequently shortened to Gill. It originates as a feminine form of the name Julian, Julio, ...

(1988) argue instead that the Estemmenosuchidae are the most basal Dinocephalia, being more primitive than both the Anteosauria and the Tapinocephalia.

Ecological succession

The Estemmenosuchids replaced the

caseids Caseidae are an Extinction, extinct Family (biology), family of Basal (phylogenetics), 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 so ...

as the dominant

megaherbivore Megaherbivores (Greek :wiktionary:μέγας, μέγας megas "large" and Latin ''herbivora'' "herbivore") are large herbivores that can exceed in weight. The earliest herbivores to reach such sizes like the Pareiasauria, pareiasaurs appeare ...

s of the

Wordian In the geologic timescale, the Wordian is an age or stage of the Permian. It is the middle of three subdivisions of the Guadalupian Epoch or Series. The Wordian lasted between and million years ago (Ma). It was preceded by the Roadian and fo ...

age (middle of the Middle Permian), before being themselves replaced by the

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 Tapinocepha ...

during the

Capitanian In the geologic timescale, the Capitanian is an age or stage of the Permian. It is also the uppermost or latest of three subdivisions of the Guadalupian Epoch or Series. The Capitanian lasted between and million years ago. It was preceded by t ...

age (late Middle Permian).

References

General references

* Olsen, E. C. (1962). "

Late Permian Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

terrestrial vertebrates, USA and USSR." ''

Transactions of the American Philosophical Society The American Philosophical Society (APS) is an American scholarly organization and learned society founded in 1743 in Philadelphia that promotes knowledge in the humanities and natural sciences through research, professional meetings, publicat ...

'' 52: 1–224. * Rubidge, B.S. &

Sidor, C.A. Christian Alfred Sidor is an American vertebrate paleontologist. He is currently a Professor in the Department of Biology, University of Washington in Seattle, as well as Curator of Vertebrate Paleontology and Associate Director for Research and C ...

(2001). "Evolutionary patterns among Permo-Triassic therapsids." ''

Annual Review of Ecology and Systematics The ''Annual Review of Ecology, Evolution, and Systematics'' is an annual scientific journal published by Annual Reviews. The journal was established in 1970 as the ''Annual Review of Ecology and Systematics'' and changed its name beginning in 200 ...

'' 32: 449–480.

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