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 or agonistic behavior. Apart from the best known genus, '' Estemmenosuchus'', the group is poorly known. To date, their fossils are known only from the Perm 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. 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'', 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), 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 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 for herbivorous dinocephalians, as opposed to the " Anteosauria" for the carnivorous forms. They suggested that Estemmenosuchids are very early/primitive members of the Tapinocephalia. However Thomas Kemp (1982) and Gillian King (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 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 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'' 52: 1–224. * Rubidge, B.S. & Sidor, C.A. (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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