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71-828: Rubidgeinae is an extinct subfamily of gorgonopsid therapsids known only from Africa . They were among the largest gorgonopsians, and their fossils are common in the Cistecephalus and Daptocephalus assemblage zones of the Karoo Basin . They lived during the Late Permian , and became extinct at the end of the Permian . Rubidgeines were large, quadrupedal carnivores of the family Gorgonopsidae . Their largest teeth are their upper canines , which were blade-like and had well-developed serrations. Their postcanine teeth were small and conical, but were also frequently serrated. Tooth replacement

142-423: A parietal eye (which detects sunlight and maintains circadian rhythm ), a keen sense of smell, a functional vomeronasal organ ("Jacobson's organ"), and possibly a rudimentary eardrum . The major therapsid groups had all evolved by 275 million years ago from a " pelycosaur " ancestor (a poorly defined group including all synapsids which are not therapsids). The therapsid takeover from pelycosaurs took place by

213-456: A bite-and-retreat tactic, ambushing and taking a debilitating bite out of the target, and following it at a safe distance before its injuries exhausted it, whereupon the gorgonopsian would grapple the animal and deliver a killing bite. They would have had an exorbitant gape, possibly in excess of 90°, without having to unhinge the jaw. They markedly increased in size as time went on, growing from small skull lengths of 10–15 cm (4–6 in) in

284-542: A certain temperature threshold, and below about 9–14 °C (48–57 °F), the honey bee reverts to ectothermy. Facultative endothermy can also be seen in multiple snake species that use their metabolic heat to warm their eggs. Python molurus and Morelia spilota are two python species where females surround their eggs and shiver in order to incubate them. Some ectotherms , including several species of fish and reptiles , have been shown to make use of regional endothermy, where muscle activity causes certain parts of

355-553: A comprehensive monograph on Gorgonopsia (defining it as an infraorder ), and recognised only two families: Watongiidae and Gorgonopidae. Watongia was moved to Varanopidae in 2004 by the Canadian paleontologists Robert R. Reisz and Michel Laurin . Sigogneau-Russell split Gorgonopidae into three subfamilies—Gorgonopsinae, Rubidgeinae, and Inostranceviinae—and reduced the number of genera to twenty-three. In 2002, Russian palaeontologist Mikhail Feodosievich Ivakhnenko , considering

426-516: A drop. The resting human body generates about two-thirds of its heat through metabolism in internal organs in the thorax and abdomen, as well as in the brain. The brain generates about 16% of the total heat produced by the body. Heat loss is a major threat to smaller creatures, as they have a larger ratio of surface area to volume . Small warm-blooded animals have insulation in the form of fur or feathers . Aquatic warm-blooded animals, such as seals , generally have deep layers of blubber under

497-474: A few more Russian taxa have been described: Pravoslavlevia , Sauroctonus , Viatkogorgon , Suchogorgon , and Nochnitsa . One of the Russian genera named, Leogorgon , is now considered as a nomen dubium . Gorgonopsians are conspicuously absent beyond these two areas. In 1979, Chinese palaeontologist Yang Zhongjian described a Chinese gorgonopsian " Wangwusaurus tayuensis " based on teeth from

568-404: A given body mass. As a consequence they also need higher food intake rates, which may limit abundance of endotherms more than ectotherms. Because ectotherms depend on environmental conditions for body temperature regulation, they typically are more sluggish at night and in the morning when they emerge from their shelters to heat up in the first sunlight. Foraging activity is therefore restricted to

639-589: A high variability (both within and between species) in their diurnal activity patterns. It is thought that the evolution of endothermia was crucial in the development of eutherian mammalian species diversity in the Mesozoic period. Endothermia gave the early mammals the capacity to be active during nighttime while maintaining small body sizes. Adaptations in photoreception and the loss of UV protection characterizing modern eutherian mammals are understood as adaptations for an originally nocturnal lifestyle, suggesting that

710-680: A large and probably rubidgeine upper jaw fragment and canine was identified at the Late Permian Moradi Formation in Niger (one of the few low-latitude Late Permian tetrapod-bearing formations), and is the first evidence of a low-latitude gorgonopsian. Upon discovery, Owen presumed that Gorgonops and several other taxa he described from the Karoo Supergroup were cold-blooded reptiles, despite bearing teeth resembling those of carnivorous mammals. He proposed classifying all of them under

781-419: A long time. On the other hand, because the functional canine is typically found in the foremost tooth socket (instead of equal occurrence in either socket), it is possible that canine replacement occurred a finite number of times, and the animal would eventually be left with a single, permanent set of functional canines in these sockets. In 1984, British palaeontologists Doris and Kenneth Kermack suggested that

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852-409: A predator. Unlike either reptiles or mammals , the semi-circular canals are flat, probably because they were wedged between the opisthotic (an inner ear bone) and supraoccipital bones. Like many mammals, gorgonopsians were heterodonts , with clearly defined incisors , canines , and postcanine teeth homologous with premolars and molars . They had five incisors in the upper jaw (for most,

923-473: A rather high body temperature, it is unclear if they would have also had sweat glands or fur (and by extension whiskers and related structures). Their brains were reminiscent of modern reptilian brains, rather than those of living mammals . Most species may have been predominantly diurnal (active during the day) though some could have been crepuscular (active at dawn or dusk) or nocturnal (active at night). They are thought to have had binocular vision ,

994-1024: A species can reproduce, as embryos are generally intolerant of thermal fluctuations that are easily tolerated by adults. Endothermy may also provide protection against fungal infection. While tens of thousands of fungal species infect insects, only a few hundred target mammals, and often only those with a compromised immune system . A recent study suggests fungi are fundamentally ill-equipped to thrive at mammalian temperatures. The high temperatures afforded by endothermy might have provided an evolutionary advantage. Ectotherms increase their body temperature mostly through external heat sources such as sunlight energy; therefore, they depend on environmental conditions to reach operational body temperatures. Endothermic animals mostly use internal heat production through metabolic active organs and tissues (liver, kidney, heart, brain, muscle) or specialized heat producing tissues like brown adipose tissue (BAT). In general, endotherms therefore have higher metabolic rates than ectotherms at

1065-526: A thick bone roof ( tectus is Latin for "covered, roofed, decked"). In 1890, English naturalist Richard Lydekker made Gorgonops the type species of the family Gorgonopsidae. British palaeontologist Harry Seeley in 1895 believed Gorgonops lacked an opening in the temporal bone (temporal fenestra), which is a diagnostic feature of Theriodontia, and so elevated Gorgonopsidae to Gorgonopsia, distinct from Theriodontia. He classified all South African materials bearing both reptilian and mammalian traits into

1136-660: Is ectothermy , although in general, there is no absolute or clear separation between the nature of endotherms and ectotherms. Endothermy was thought to have originated towards the end of the Permian Period . One recent study claimed the origin of endothermy within Synapsida (the mammalian lineage) was among Mammaliamorpha , a node calibrated during the Late Triassic period, about 233 million years ago. Another study instead argued that endothermy only appeared later, during

1207-593: Is described in 2022 by paleontologists Jun Liu and Wan Yiang and confirms that it comes from a gorgonopsian dating from the Upper Permian that actually lived in present-day China. In 2003, Indian palaeontologists Sanghamitra Ray and Saswati Bandyopadhyay assigned some skull fragments from the Late Permian Kundaram Formation to a medium-sized gorgonopsian, though the gorgonopsian characteristics have also been documented in some therocephalians. In 2008,

1278-517: Is little consensus on which genera can be assigned to which subfamilies. In 2015, American palaeontologist Christian F. Kammerer and colleagues redescribed Eriphostoma (which was labelled as an indeterminate theriodont) as a gorgonopsian, and sunk Scylacognathus and the next year Eoarctops into it. The first phylogeny (family tree) of the members of Gorgonopsia was published in 2016 by American palaeontologist Christian F. Kammerer, who specifically investigated Rubidgeinae, and re-described both

1349-531: Is possible that some taxa are synonymous with each other, and represent different stages of development. Among the first attempts to organise the clade was carried out by British zoologist David Meredith Seares Watson and American palaeontologist Alfred Romer in 1956, who split it into twenty families, of which the members of three (Burnetiidae, Hipposauridae, and Phthinosuchidae) are not considered gorgonopsians anymore. In 1970 and again in 1989, predominantly considering African taxa, Sigogneau-Russell published

1420-409: Is related to the vestibulo–ocular reflex (which stabilises gaze while moving the head). Judging by the orientation of the semi-circular canals in the ear (which have to be oriented parallel to the ground), the head of the gorgonopsian specimen GPIT/RE/7124 would have tilted forward by about 41°, increasing the overlap between the visual fields of the two eyes and improving binocular vision —useful to

1491-401: Is short but longer and slenderer than the humerus . For most, the tibia and fibula strongly curve into each other, and the tibia is more robust than the fibula. The joint between the ankle and the heel bones may have been somewhat mobile. The fifth digit for both the hands and feet was not attached to the carpus / tarsus , and instead connected directly to the ulna /heel bone. In 1876,

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1562-468: The Middle Jurassic , among crown-group mammals. Evidence for endothermy has been found in basal synapsids (" pelycosaurs "), pareiasaurs , ichthyosaurs , plesiosaurs , mosasaurs , and basal archosauromorphs . Even the earliest amniotes might have been endotherms. Many endotherms have a larger amount of mitochondria per cell than ectotherms. This enables them to generate heat by increasing

1633-683: The Moradi Formation of Niger, western Russia, and in the Turpan Basin of Xinjiang , China , with probable remains known from the Kundaram Formation in the Pranhita–Godavari Basin of India . These places were semi-arid areas with highly seasonal rainfall. Gorgonopsian genera are all very similar in appearance, and consequently many species have been named based on flimsy and likely age-related differences since their discovery in

1704-692: The Upper Luangwa Valley of Zambia , and Chiweta , Malawi . Gorgonopsians were first identified in Russia in the 1890s at the Sokolki locality on the Northern Dvina in Siberia under the supervision of Russian palaeontologist Vladimir Prokhorovich Amalitskii . In a posthumous publication, it was described as Inostrancevia alexandri , and it is one of the best known and largest gorgonopsians. Since then, only

1775-1343: The Wordian . The oldest gorgonopsian specimen is a partial snout belonging to an undeterminable genus from the Eodicynodon Assemblage Zone of the Karoo Basin, roughly dating to the Wordian. Phorcys known from the lowermost end of Karoo's Tapinocephalus Assemblage Zone , roughly dating a little later to the Wordian/Capitanian boundary, is the oldest identifiable gorgonopsian taxon. Sphenacodontidae Biarmosuchia Dinocephalia Anomodontia Gorgonopsia Therocephalia Endotherms Only birds and mammals are considered truly endothermic groups of animals. However, Argentine black and white tegu , leatherback sea turtles , lamnid sharks, tuna and billfishes , cicadas , and winter moths are mesothermic . Unlike mammals and birds, some reptiles, particularly some species of python and tegu , possess seasonal reproductive endothermy in which they are endothermic only during their reproductive season . In common parlance, endotherms are characterized as " warm-blooded ". The opposite of endothermy

1846-581: The ozone layer . However, some smaller taxa like Cyonosaurus may have survived up to the Early Triassic . The large predatory niches would be taken over by the archosaurs (namely crocodilians and dinosaurs ) in the Mesozoic . Earlier gorgonopsids in the Middle Permian were quite small, with skull lengths of 10–15 cm (4–6 in), whereas some later genera attained massive, bear-like sizes with

1917-459: The skin and any pelage (fur) that they might have; both contribute to their insulation. Penguins have both feathers and blubber. Penguin feathers are scale-like and serve both for insulation and streamlining. Endotherms that live in very cold circumstances or conditions predisposing to heat loss, such as polar waters, tend to have specialised structures of blood vessels in their extremities that act as heat exchangers . The veins are adjacent to

1988-998: The tribe Rubidgeini pending further examination. In 2018, Kammerer and Russian palaeontologist Vladimir Masyutin identified a new genus Nochnitsa as the basalmost known gorgonopsians, and found that all Russian taxa (except Viatkogorgon , which is in the outclade) form a completely separate clade from the African taxa. Also in 2018, palaeobiologist Eva-Maria Bendel, Kammerer, and colleagues resurrected Cynariops . In 2022, Kammerer and fellow palaeontologist Bruce S. Rubidge described Phorcys from South Africa. Nochnitsa Viatkogorgon Suchogorgon Sauroctonus Pravoslavlevia Inostrancevia Phorcys Eriphostoma Gorgonops Cynariops Lycaenops Smilesaurus Arctops Arctognathus Aelurognathus Ruhuhucerberus Sycosaurus Leontosaurus Dinogorgon Rubidgea Clelandina Synapsida has traditionally been split into

2059-425: The 3 ridges. They typically feature a long and narrow skull. Juvenile Rubidgea appear to have had snouts wider than long. Unlike eutheriodonts, the occipital bone (at the back of the skull) is rectangular (wider than tall) and concave, as opposed to triangular. The gorgonopsian brain, like other non- mammaliaform therapsids , lacks an expansion of the neocortex , has a relatively large hindbrain compared to

2130-645: The Greek Gorgon , a mythological beast, and óps 'aspect') is an extinct clade of sabre-toothed therapsids from the Middle to the Upper Permian , roughly between 265 and 252 million years ago. They are characterised by a long and narrow skull, as well as elongated upper and sometimes lower canine teeth and incisors which were likely used as slashing and stabbing weapons. Postcanine teeth are generally reduced or absent. For hunting large prey, they possibly used

2201-584: The Late Permian Jiyuan Formation , but in 1981, palaeontologists Denise Sigogneau-Russell and Ai-Lin Sun found the assigned material to be a random assemblage of which only two have even a remote similarity to Gorgonopsia. In 2011, an incomplete set of teeth were discovered in a locality within the Turpan Depression , Xinjiang , in the northwest of the country. The fossil material, although thin,

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2272-694: The Middle Permian as the world progressively became drier. Gorgonopsians rose to become apex predators of their environments following the Capitanian mass extinction event which killed off the dinocephalians and some large therocephalians after the Middle Permian. Despite the existence of a single continent during the Permian, Pangaea , gorgonopsians have only been found in the Karoo Supergroup (primarily in South Africa, but also in Tanzania, Zambia, and Malawi),

2343-659: The Middle Permian to bear -like proportions of up to 60 cm (2 ft) in the Upper Permian. The latest gorgonopsians, Rubidgeinae , were the most robust of the group and could produce especially powerful bites. Gorgonopsians are thought to have been completely terrestrial and could walk with a semi-erect gait, with a similar terrestrial locomotory range as modern crocodilians . They may have been more agile than their prey items, but were probably inertial homeotherms rather than endotherms unlike contemporary therocephalians and cynodonts , and thus were probably comparatively less active. Though gorgonopsians were able to maintain

2414-646: The Reverend John H. Whaits, Broom reinstated Gorgonopsia. The number of South African genera rapidly grew in the 20th-century, headed principally by Broom, whose extensive work on the Karoo therapsids—from the beginning of his career in the country in 1897 to his death in 1951—led to his description of 57 gorgonopsian holotype specimens and 29 genera. Many of Broom's taxa would later be invalidated. Many other contemporary workers created wholly new species or genera based on single specimens. Consequently, Gorgonopsia has been

2485-518: The Russian taxa, instead considered Gorgonopsia a suborder, and grouped it together with Dinocephalia into the order "Gorgodontia". He divided Gorgonopsia into the superfamilies "Gorgonopioidea" (families Gorgonopidae, Cyonosauridae, and Galesuchidae) and "Rubidgeoidea" (Rubidgeidae, Phtinosuchidae, and Inostranceviidae). In 2007, biologist Eva V. I. Gebauer, in her comprehensive review of Gorgonopsia (her PhD dissertation), rejected Ivakhnenko's model in favour of Sigogneau-Russell's, and further reduced

2556-460: The adaptive shift from pelycosaur-grade to therapsid-grade took place during the Middle Permian ( Olson's Extinction ); however, the classification of those "therapsids" and the age of the formations have since been challenged. Thus, the exact timing of the therapsid takeover is unclear, but the six major therapsid groups ( Biarmosuchia , Dinocephalia , Anomodontia , Gorgonopsia, Therocephalia, and Cynodontia) had evolved by 265 million years ago during

2627-430: The arteries full of warm blood. Some of the arterial heat is conducted to the cold blood and recycled back into the trunk. Birds, especially waders , often have very well-developed heat exchange mechanisms in their legs—those in the legs of emperor penguins are part of the adaptations that enable them to spend months on Antarctic winter ice. In response to cold, many warm-blooded animals also reduce blood flow to

2698-788: The basal " Pelycosauria " and the derived Therapsida. The former comprises cold-blooded creatures with a sprawling gait and presumably lower metabolism which evolved in the Upper Carboniferous . Through the middle to late 20th-century, American palaeontologist Everett C. Olson investigated synapsid diversity in the Middle Permian San Angelo , Flowerpot , and Chickasha Formations in North America, and noted that pelycosaur diversity reduced from six to three in these formations, and that they coexisted with several fragmentary specimens which he interpreted as therapsids. He then suggested

2769-583: The blood to cool, which reduces their core body temperature when the blood moves through the rest of the circulatory system. The major advantage of endothermy over ectothermy is decreased vulnerability to fluctuations in external temperature. Regardless of location (and hence external temperature), endothermy maintains a constant core temperature for optimal enzyme activity. Endotherms control body temperature by internal homeostatic mechanisms. In mammals, two separate homeostatic mechanisms are involved in thermoregulation—one mechanism increases body temperature, while

2840-423: The body to remain at higher temperatures than the rest of the body. This allows for better locomotion and use of the senses in cold environments. Students encounter a source of possible confusion between the terminology of physics and biology. Whereas the thermodynamic terms " exothermic " and " endothermic " respectively refer to processes that give out heat energy and processes that absorb heat energy, in biology

2911-436: The canines grew to match the size of the skull, and continually broke off until the animal stopped growing, and that gorgonopsians featured an early version of finite tooth replacement exhibited in many mammals. The tooth replacement patterns of the other teeth are unclear. The postcanine teeth were replaced more slowly than the other teeth, likely due to their lack of functional significance. The seven cervical vertebrae (in

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2982-468: The cervical vertebrae is overall reptilian, permitting side-to-side movement of the head but restricting up-and-down motion. The last cervical is shaped more like the dorsal vertebrae . The dorsals are spool-shaped and all appear about the same as each other. The spinous processes jut out steeply from the centra, and feature sharp keels on the front and back sides. Unlike eutheriodonts, gorgonopsians do not have distinguished lumbar vertebrae . Nonetheless,

3053-498: The day in nocturnal animals, thus reducing the energy cost of maintaining body temperature. Less drastic intermittent reduction in body temperature also occurs in other larger endotherms; for example human metabolism also slows down during sleep, causing a drop in core temperature, commonly of the order of 1 degree Celsius. There may be other variations in temperature, usually smaller, either endogenous or in response to external circumstances or vigorous exertion, and either an increase or

3124-415: The daytime (diurnal activity patterns) in most vertebrate ectotherms. In lizards, for instance, only a few species are known to be nocturnal (e.g. many geckos) and they mostly use 'sit and wait' foraging strategies that may not require body temperatures as high as those necessary for active foraging. Endothermic vertebrate species are, therefore, less dependent on the environmental conditions and have developed

3195-405: The diurnal cycle in places of sharp temperature variations between day and night and during more of the year in places of great seasonal differences of temperature. This is accompanied by the need to expend more energy to maintain the constant internal temperature and a greater food requirement. Endothermy may be important during reproduction, for example, in expanding the thermal range over which

3266-417: The dorsals equating to that series are similar to the lumbars of sabre-toothed cats with steeply oriented zygopophases, useful in stabilising the lower back especially when pinning down struggling prey. There are three sacral vertebrae , and the series attached to the pelvis by the first vertebra. The pelvis is reptilian, with separated ilium , ischium , and pubis . The femur is slightly s-shaped, and

3337-535: The first gorgonopsian remains were identified in the Beaufort Group of the Karoo Supergroup of South Africa, by the biologist and paleontologist Richard Owen . He classified the fossils as Gorgonops torvus , combining the Greek Gorgon , a mythological beast, with the word óps ( ὄψ ), meaning 'aspect'. In Africa, gorgonopsians have also been found in Karoo outcroppings in the Ruhuhu Valley of Tanzania,

3408-405: The first three were the same size as each other, and the last two were shorter) and four on the bottom. In the majority of gorgonopsians, the incisors were large, and the upper canines were elongated into sabres, much like those of later sabre-toothed cats . Some gorgonopsians had exceptionally long upper canines, such as Inostrancevia , and some of them had a flange on the lower jaw to sheath

3479-406: The forebrain, a large epyphysial nerve (found in creatures with a parietal eye on the top of the head), an enlarged pituitary gland , and an overall elongated shape; all-in-all resembling a reptilian brain. The braincase was also rather reptilian, and is also comparatively smaller and not as thick as those of mammals. The flocculus , a lobe of the cerebellum , is proportionally large, and

3550-530: The fossil record, including theropod dinosaurs . The presence of this skull morphology is one of multiple adaptations seen in predators that utilize the skull, rather than the limbs, in prey capture. Below is a cladogram by Kammerer in 2016. Smilesaurus ferox Aelurognathus tigriceps Ruhuhucerberus haughtoni Sycosaurus laticeps Sycosaurus nowaki Leontosaurus vanderhosti Dinogorgon rubidgei Rubidgea atrox Clelandina rubidgei Gorgonopsid Gorgonopsia (from

3621-422: The fragile canines. Similar ridges have been identified on the machairodont Homotherium . The postcanine teeth were reduced in both size and number; many rubidgeines (the latest gorgonopsians) did not have postcanines in the lower jaw, and Clelandina lacked them entirely. Gorgonopsians were polyphyodonts , and teeth grew continuously throughout an individual's life. Like some therapsids, while there

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3692-682: The group went through an evolutionary bottleneck (the nocturnal bottleneck hypothesis ). This could have avoided predator pressure from diurnal reptiles and dinosaurs, although some predatory dinosaurs, being equally endothermic, might have adapted a nocturnal lifestyle in order to prey on those mammals. Many insect species are able to maintain a thoracic temperature above the ambient temperature using exercise. These are known as facultative or exercise endotherms. The honey bee , for example, does so by contracting antagonistic flight muscles without moving its wings (see insect thermoregulation ). This form of thermogenesis is, however, only efficient above

3763-469: The largest being Inostrancevia up to 3.5 m (11 ft) in length and 300 kg (660 lb) in body mass. Nonetheless, small gorgonopsians remained abundant until extinction (though small species may actually represent juvenile specimens of other taxa). Like other Permian therapsids, gorgonopsians had developed several mammalian characteristics. These might have included a parasagittal gait (the limbs were vertically oriented and moved parallel to

3834-399: The largest known from Africa . They were also the largest predators in their environment. Their massive canines and serrated teeth indicate that they were adapted for macropredation . The robust skull roof and supraorbital bosses of rubidgeines likely acted to protect the skull from the stress inflicted during prey capture, and similar morphology has been seen in many other macropredators in

3905-579: The late 19th century, and the group has been subject to several taxonomic revisions. Most gorgonopsians became extinct during a phase of the Permian–Triassic extinction event taking place at the very end of the Permian, in which major volcanic activity (which would produce the Siberian Traps ) and resultant massive spike in greenhouse gases caused rapid aridification due to temperature spike, acid rain , frequent wildfires , and potential breakdown of

3976-423: The mouth from the nasal cavity, prohibiting chewing. Anatomy varies incredibly little between gorgonopsians. Many species are distinguished by vague proportional differences, and consequently smaller species may actually represent juveniles of larger taxa. Notably, the vomer at the tip of the snout varies among species in terms of the degree of its expansion, as well as the positions, degree of splay, and shape of

4047-403: The neck) are all the same size as each other except for the last one, which is shorter and lower; there is one atlas and one axis . Like sabre-toothed cats, the neck is long with well-developed muscles, which would have been especially useful when the canines were sunk into an animal. Like other early synapsids, gorgonopsians have a single occipital condyle , and the articulation (the joints) of

4118-423: The need to avoid hyperthermia . Endothermy does not provide greater speed in movement than ectothermy (cold-bloodedness)—ectothermic animals can move as fast as warm-blooded animals of the same size and build when the ectotherm is near or at its optimal temperature, but often cannot maintain high metabolic activity for as long as endotherms. Endothermic/homeothermic animals can be optimally active at more times during

4189-407: The newly coined order Theriodontia (which he placed in the class Reptilia). He decided to subdivide Theriodontia into families based on the anatomy of the nostrils (the bony narials)—"Mononarialia" for those with one opening in the skull for the nose as in mammals, "Binarialia" for those with two openings as in reptiles, and "Tectinarialia" for Gorgonops because its opening was overshadowed by

4260-416: The number of genera to fourteen in addition to the Russian genera: Aloposaurus , Cyonosaurus , Aelurosaurus , Sauroctonus , Scylacognathus , Eoarctops , Gorgonops , " Dixeya " nasuta (under the informal nomen nudum " Njalila "), Lycaenops , Arctognathus , Aelurognathus , Sycosaurus , Clelandina , and Rubidgea . In general, Sigogneau-Russell's model is supported, but there

4331-670: The order "Theriosuchia", and considered Gorgonopsia and Theriodontia suborders of it. American palaeontologist Henry Fairfield Osborn completely reworked the classification of Reptilia in 1903, and erected two major groups: Diapsida and Synapsida , and in 1905, South African palaeontologist Robert Broom created a third group, Therapsida , to house the "mammal-like reptiles", including Theriodontia. He also challenged Seeley's claim and relegated Gorgonops back to Theriodontia, but he placed it into his newly erected subgroup Therocephalia , dissolving Gorgonopsia. In 1913, especially in light of an almost complete G. torvus skull discovered by

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4402-404: The other decreases it. The presence of two separate mechanisms provides a very high degree of control. This is important because the core temperature of mammals can be controlled to be as close as possible to the optimal temperature for enzyme activity. The overall rate of an animal's metabolism increases by a factor of about two for every 10 °C (18 °F) rise in temperature , limited by

4473-760: The rate at which they metabolize fats and sugars . Accordingly, to sustain their higher metabolism, endothermic animals typically require several times as much food as ectothermic animals do, and usually require a more sustained supply of metabolic fuel. In many endothermic animals, a controlled temporary state of hypothermia conserves energy by permitting the body temperature to drop nearly to ambient levels. Such states may be brief, regular circadian cycles called torpor , or they might occur in much longer, even seasonal, cycles called hibernation . The body temperatures of many small birds (e.g. hummingbirds ) and small mammals (e.g. tenrecs ) fall dramatically during daily inactivity, such as nightly in diurnal animals or during

4544-404: The skin by vasoconstriction to reduce heat loss. As a result, they blanch (become paler). In equatorial climates and during temperate summers, overheating ( hyperthermia ) is as great a threat as cold. In hot conditions, many warm-blooded animals increase heat loss by panting, which cools the animal by increasing water evaporation in the breath, and/or flushing, increasing the blood flow to

4615-405: The skin so the heat will radiate into the environment. Hairless and short-haired mammals, including humans and horses, also sweat , since the evaporation of the water in sweat removes heat. Elephants keep cool by using their huge ears like radiators in automobiles. Their ears are thin and the blood vessels are close to the skin, and flapping their ears to increase the airflow over them causes

4686-425: The spine) as opposed to the sprawling gait of amphibians and earlier synapsids. This gait change in therapsids was possibly related to the reduction in tail size and phalangeal formula (the number of bones per digit, which for gorgonopsians was 2.3.4.5.3 like reptiles ). Other developments included fibrous lamellar cortical bone and deeply-set teeth. Like reptiles, gorgonopsians lack a secondary palate separating

4757-401: The subfamily and the nine species he assigned to it (reducing the number from thirty-six species). Kammerer also resurrected Dinogorgon , Leontosaurus , Ruhuhucerberus , and Smilesaurus . Kammerer was unsure if Leontosaurus , Clelandina , Dinogorgon , and Rubidgea all represent the same taxon or not (for which Dinogorgon has priority ), but he decided to classify all of them in

4828-466: The subject of much taxonomic turmoil, and is one of the most problematic synapsid groups. Because the skull anatomy differs very little across taxa, many are defined based on vague proportional differences, including even the well-known members. Nominal species are distinguished predominantly by traits which are known to be quite variable depending on the age of the individual, including eye orbit size, snout length, and number of postcanine teeth. Thus, it

4899-609: The tip of the canine while the mouth was closed. Sabres are generally interpreted as having been used as stabbing or slashing weapons, which would have required an extremely wide gape. Both the upper and lower canines of Rubidgea were elongated, and the animal would have needed an even greater gape. The serration pattern of gorgonopsians was most similar to those of theropod dinosaurs than to other synapsids. The palate also features tuberosities and ridges which oftentimes have functional teeth, which may have been used to hold onto struggling prey, diverting these powerful forces away from

4970-490: Was one functional canine, another canine was growing to replace it when it inevitably broke off. The left and right sides of the jaws did not have to be synchronous, so, for example, the first canine on the left side could be functional while the first canine on the right side was still growing. Such a method might have been in play so as always to have a set of functional canines, as having a single or no canines would have severely impeded hunting, and growing such large teeth took

5041-409: Was rapid relative to basal therocephalians. Rubidgeines can be distinguished from other gorgonopsians by the absence of a blade-like parasphenoid bone and reduced or absent preparietal bone. The jugal bone, while narrow in most gorgonopsians, was often broadly expanded in rubidgeines. The largest rubidgeins were Dinogorgon and Rubidgea . Rubidgeines were among the largest gorgonopsians known, and

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