Estemmenosuchidae is an extinct

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of large, very early

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 mouthpart ...

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 during the

Guadalupian 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 ± 0. ...

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

display Display may refer to: Technology * Display device, output device for presenting information, including: ** Cathode ray tube, video display that provides a quality picture, but can be very heavy and deep ** Electronic visual display, output devi ...

agonistic behavior Agonistic behaviour is any social behaviour related to fighting. The term has broader meaning than aggressive behaviour because it includes threats, displays, retreats, placation, and conciliation. The term "agonistic behaviour" was first implemen ...

. Apart from the best known genus, ''

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 ...

'', 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 administra ...

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 P ...

. 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, whe ...

s and

canine teeth In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, or (in the context of the upper jaw) fangs, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. They can appear more flattened howeve ...

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'' ('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 ...

'', 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. Dinoceph ...

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 !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 ext ...

(

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 underlie ...

), 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 (; ) 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 typically shared derived char ...

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. No ...

for herbivorous dinocephalians, as opposed to the " Anteosauria" 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) ...

(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 μέγας megas "large" and Latin ''herbivora'' "herbivore") are large terrestrial herbivores that can exceed in weight. This polyphyletic group of megafauna includes elephants, rhinos, hippos, and giraffes. The largest bo ...

s of the Wordian age (middle of the Middle Permian), before being themselves replaced by the Tapinocephalidae during the Capitanian age (late Middle Permian).

References

General references

* Olsen, E. C. (1962). " Late Permian terrestrial vertebrates, USA and USSR." ''

Transactions of the American Philosophical Society The American Philosophical Society (APS), founded in 1743 in Philadelphia, is a scholarly organization that promotes knowledge in the sciences and humanities through research, professional meetings, publications, library resources, and communit ...

'' 52: 1–224. * Rubidge, B.S. & Sidor, C.A. (2001). "Evolutionary patterns among Permo-Triassic therapsids." '' Annual Review of Ecology and Systematics'' 32: 449–480.

External links