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Therocephalia is an extinct suborder of eutheriodont therapsids from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their teeth, suggest that they were carnivores. Like other non-mammalian synapsids, therocephalians are described as mammal-like reptiles. Therocephalia is the group most closely related to the cynodonts, which gave rise to the mammals. This relationship takes evidence in a variety of skeletal features. The phylogeny of therocephalians has been disputed, as the monophyly of the group and the relationships of its members are unclear. The fossils of therocephalians are numerous in the Karoo of South Africa, but have also been found in Russia, China, and Antarctica. Early therocephalian fossils discovered in Middle Permian deposits of South Africa support a Gondwanan origin for the group, which seems to have spread quickly throughout the world. Although almost every therocephalian lineage ended during the great Permian–Triassic extinction event, a few representatives of the subgroup called Eutherocephalia survived into the Early Triassic. However, the last therocephalians became extinct by the early Middle Triassic, possibly due to climate change and competition with cynodonts and various groups of reptiles. ==Anatomy and physiology== Like the gorgonopsids and many cynodonts, most therocephalians were presumably carnivores. The earlier therocephalians were in many respects as primitive as the gorgonopsids, but they did show certain advanced features. There is an enlargement of the temporal opening for broader jaw adductor muscle attachment and a reduction of the phalanges (finger and toe bones) to the mammalian phalangeal formula. The presence of an incipient secondary palate in advanced therocephalians is another feature shared with mammals. The discovery of maxilloturbinal ridges in forms such as the primitive therocephalian ''Glanosuchus'', suggests that at least some therocephalians may have been warm-blooded. The later therocephalians included the advanced Baurioidea, which carried some theriodont characteristics to a high degree of specialization. For instance, small baurioids and the herbivorous ''Bauria'' did not have an ossified postorbital bar separating the orbit from the temporal opening—a condition typical of primitive mammals. These and other advanced features led to the long-held opinion, now rejected, that the ictidosaurs and even some early mammals arose from a baurioid therocephalian stem. Mammalian characteristics such as this seem to have evolved in parallel among a number of different therapsid groups, even within Therocephalia. Several more specialized lifestyles have been suggested for some therocephalians. Many small forms like ictidosuchids have been interpreted as aquatic animals. Evidence for aquatic lifestyles includes sclerotic rings that may have stabilized the eye under the pressure of water and strongly developed cranial joints, which may have supported the skull when consuming large fish and aquatic invertebrates. One therocephalian, ''Nothogomphodon'', had large saber-like canine teeth and may have fed on large animals, including other therocephalians. Other therocephalians such as bauriids and nanictidopids have wide teeth with many ridges similar to those of mammals, and may have been herbivores. Many small therocephalians have small pits on their snouts that probably supported vibrissae or whiskers. In 1994, Russian paleontologist Leonid Tatarinov proposed that these pits were part of an electroreception system in aquatic therocephalians. However, it is more likely these pits are enlarged versions of the ones thought to support whiskers, or holes for blood vessels in a fleshy lip.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Therocephalia」の詳細全文を読む スポンサード リンク
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