49-529: Therapsida is a clade comprising a major group of eupelycosaurian synapsids that includes mammals and their ancestors and close relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more underneath the body, resulting in a more "standing" quadrupedal posture, as opposed to the lower sprawling posture of many reptiles and amphibians . Therapsids evolved from earlier synapsids commonly called " pelycosaurs ", specifically within
98-602: A lesser extent in parts of what are now India, China, Mongolia, European Russia, and Antarctica (which was not over the South Pole at the time). Most Lystrosaurus fossils have been found in the Balfour and Katberg Formations of the Karoo basin in South Africa ; these specimens offer the best prospects of identifying species because they are the most numerous and have been studied for
147-406: A lineage of the eucynodont suborder. Biarmosuchia Dinocephalia Anomodontia Gorgonopsia Therocephalia Cynodontia Six major groups of therapsids are generally recognized: Biarmosuchia , Dinocephalia , Anomodontia , Gorgonopsia , Therocephalia and Cynodontia . A clade uniting therocephalians and cynodonts, called Eutheriodontia , is well supported, but relationships among
196-399: A mutation in the regulatory gene Msx2, which is involved in both the closure of the skull roof and the maintenance of hair follicles in mice. This suggests that hair may have first evolved in probainognathians, though it does not entirely rule out an earlier origin of fur. Whiskers probably evolved in probainognathian cynodonts. Some studies had inferred an earlier origin for whiskers based on
245-438: A small dog to 8 feet (2.5 meters) long. As a dicynodont, Lystrosaurus had only two teeth (a pair of tusk -like canines ), and is thought to have had a horny beak that was used for biting off pieces of vegetation. Lystrosaurus was a heavily built, herbivorous animal. The structure of its shoulders and hip joints suggests that Lystrosaurus moved with a semi-sprawling gait . The forelimbs were even more robust than
294-508: A while, 95% of land vertebrates were Lystrosaurus . This is the only time that a single species or genus of land animal dominated the Earth to such a degree. A few other Permian therapsid genera also survived the mass extinction and appear in Triassic rocks—the therocephalians Tetracynodon , Moschorhinus , Ictidosuchoides and Promoschorhynchus —but do not appear to have been abundant in
343-424: Is an extinct genus of herbivorous dicynodont therapsids from the late Permian and Early Triassic epochs (around 248 million years ago). It lived in what is now Antarctica , India , China , Mongolia , European Russia and South Africa . Four to six species are currently recognized, although from the 1930s to 1970s the number of species was thought to be much higher. They ranged in size from that of
392-529: Is notable for dominating southern Pangaea for millions of years during the Early Triassic . At least one unidentified species of this genus survived the end-Permian mass extinction and, in the absence of predators and herbivorous competitors, went on to thrive and re-radiate into a number of species within the genus, becoming the most common group of terrestrial vertebrates during the Early Triassic; for
441-474: Is poorly known, and there are few fossils that provide direct evidence for the presence or absence of fur. The most basal synapsids with unambiguous direct evidence of fur are docodonts , which are mammaliaforms very closely related to crown-group mammals. Two "mummified" juvenile specimens of the dicynodont Lystrosaurus murrayi preserve skin impressions; the skin is hairless, leathery, and dimpled, somewhat comparable to elephant skin. Fossilized facial skin from
490-476: Is poorly understood. Most Permian therapsids had a pineal foramen, indicating that they had a parietal eye like many modern reptiles and amphibians. The parietal eye serves an important role in thermoregulation and the circadian rhythm of ectotherms, but is absent in modern mammals, which are endothermic . Near the end of the Permian, dicynodonts, therocephalians and cynodonts show parallel trends towards loss of
539-607: The Carnian (Late Triassic), although they continued for some time longer in the wet equatorial band and the south. Some exceptions were the still further derived eucynodonts . At least three groups of them survived. They all appeared in the Late Triassic period. The extremely mammal -like family, Tritylodontidae , survived into the Early Cretaceous . Another extremely mammal-like family, Tritheledontidae , are unknown later than
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#1732859452357588-821: The Damodar Valley and the Kamthi Formation of the Pranhita-Godavari Basin in India . Seven Lystrosaurus species have been described from the Early Triassic Jiucaiyuan , Guodikeng and Wutonggou formations of the Bogda Mountains in Xinjiang , China , although it is possible that only two ( L. youngi and L. hedini ) are valid; unusually, no Chinese Lystrosaurus specimens are known below
637-469: The Early Cretaceous . Therapsids' temporal fenestrae were larger than those of the pelycosaurs. The jaws of some therapsids were more complex and powerful, and the teeth were differentiated into frontal incisors for nipping, great lateral canines for puncturing and tearing, and molars for shearing and chopping food. Therapsid legs were positioned more vertically beneath their bodies than were
686-658: The Moscow Basin in Russia. It was probably closely related to the African Lystrosaurus curvatus , which is regarded as one of the least specialized species and has been found in very Late Permian and very Early Triassic sediments. L. murrayi , in addition to two undescribed species presently assigned to L. curvatus and L. declivis , is known from the Early Triassic Panchet Formation of
735-666: The Sphenacodontia , more than 279.5 million years ago. They replaced the pelycosaurs as the dominant large land animals in the Guadalupian through to the Early Triassic. In the aftermath of the Permian–Triassic extinction event , therapsids declined in relative importance to the rapidly diversifying archosaurian sauropsids ( pseudosuchians , dinosaurs and pterosaurs , etc.) during the Middle Triassic. The therapsids include
784-527: The Theriodontia . Hopson and Barghausen did not initially come to a conclusion about how dinocephalians, anomodonts and theriodonts were related to each other, but subsequent studies suggested that anomodonts and theriodonts should be classified together as the Neotherapsida. However, there remains debate over these relationships; in particular, some studies have suggested that anomodonts, not gorgonopsians, are
833-581: The Transantarctic Mountains by Edwin H. Colbert and his team in 1969–1970 helped support the hypothesis of plate tectonics and strengthen the theory, since Lystrosaurus had already been found in the lower Triassic of southern Africa as well as in India and China. Lystrosaurus fossils have been found in many Late Permian and Early Triassic terrestrial bone beds , most abundantly in Africa, and to
882-612: The cynodonts , the group that gave rise to mammals ( Mammaliaformes ) in the Late Triassic around 225 million years ago, the only therapsid clade that survived beyond the end of the Triassic . The only other group of therapsids to have survived into the Late Triassic , the dicynodonts , became extinct towards the end of the period. The last surviving group of non-mammaliaform cynodonts were the Tritylodontidae , which became extinct during
931-401: The dinocephalians , the herbivorous anomodonts , the carnivorous biarmosuchians , and the mostly carnivorous theriodonts . After a brief burst of evolutionary diversity, the dinocephalians died out in the later Middle Permian ( Guadalupian ) but the anomodont dicynodonts as well as the theriodont gorgonopsians and therocephalians flourished, being joined at the very end of the Permian by
980-450: The tusk -like upper canines . Dicynodonts are generally thought to have had horny beaks like those of turtles, for shearing off pieces of vegetation, which were then ground on a horny secondary palate when the mouth was shut. The jaw joint was weak and moved backwards and forwards with a shearing action, instead of the more common sideways or up and down movements. It is thought that the jaw muscles were attached unusually far forward on
1029-587: The American Philosophical Society in 1870. Its name is derived from the Ancient Greek words listron , "shovel", and sauros , "lizard". Marsh belatedly purchased the skull in May ;1871, although his interest in an already-described specimen was unclear; he may have wanted to carefully scrutinize Cope's description and illustration. The discovery of Lystrosaurus fossils at Coalsack Bluff in
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#17328594523571078-599: The Early Jurassic . Mammaliaformes was the third group, including Morganucodon and similar animals. Some taxonomists refer to these animals as "mammals", though most limit the term to the mammalian crown group . The non-eucynodont cynodonts survived the Permian–Triassic extinction; Thrinaxodon , Galesaurus and Platycraniellus are known from the Early Triassic . By the Middle Triassic , however, only
1127-580: The Early Permian of the United States has been hypothesized to be an even earlier-diverging therapsid, but more recent study has suggested it is more likely to be a non-therapsid sphenacodontian. Biarmosuchia is the most recently recognized therapsid clade, first recognized as a distinct lineage by Hopson and Barghausen in 1986 and formally named by Sigogneau-Russell in 1989. Most biarmosuchians were previously classified as gorgonopsians. Biarmosuchia includes
1176-586: The Karoo from an area in which Late Permian sediments have not been found. L. curvatus is found in a relatively narrow band of sediments from shortly before and after the extinction, and can be used as an approximate marker for the boundary between the Permian and Triassic periods. A skull identified as L. curvatus has been found in late Permian sediments from Zambia . For many years it had been thought that there were no Permian specimens of L. curvatus in
1225-474: The Karoo, which led to suggestions that L. curvatus immigrated from Zambia into the Karoo. However, a re-examination of Permian specimens in the Karoo has identified some as L. curvatus , and there is no need to assume immigration. L. murrayi and L. declivis are found only in Triassic sediments. Lystrosaurus georgi fossils have been found in the Earliest Triassic sediments of
1274-577: The Permian-Triassic boundary in this region. L. curvatus , L. murrayi , and L. maccaigi are known from the Fremouw Formation in the Transantarctic Mountains of Antarctica . Lystrosaurus was a dicynodont therapsid , between 0.6 to 2.5 m (2 to 8 ft) long with an average of about 0.9 m (3 ft) depending upon the species. Unlike other therapsids, dicynodonts had very short snouts and no teeth except for
1323-519: The Wikimedia System Administrators, please include the details below. Request from 172.68.168.226 via cp1108 cp1108, Varnish XID 769688431 Upstream caches: cp1108 int Error: 429, Too Many Requests at Fri, 29 Nov 2024 05:50:52 GMT Lystrosaurus murrayi Lystrosaurus ( / ˌ l ɪ s t r oʊ ˈ s ɔːr ə s / ; 'shovel lizard'; proper Greek is λίστρον lístron ‘tool for leveling or smoothing, shovel, spade, hoe’)
1372-490: The dinocephalian Estemmenosuchus has been described as showing that the skin was glandular and lacked both scales and hair. Coprolites containing what appear to be hairs have been found from the Late Permian . Though the source of these hairs is not known with certainty, they may suggest that hair was present in at least some Permian therapsids. The closure of the pineal foramen in probainognathian cynodonts may indicate
1421-472: The distinctive Burnetiamorpha , but support for the monophyly of Biarmosuchia is relatively low. Many biarmosuchians are known for extensive cranial ornamentation. Dinocephalia comprises two distinctive groups, the Anteosauria and Tapinocephalia . Historically, carnivorous dinocephalians, including both anteosaurs and titanosuchids, were called titanosuchians and classified as members of Theriodontia, while
1470-438: The eucynodonts remained. The therocephalians , relatives of the cynodonts, managed to survive the Permian–Triassic extinction and continued to diversify through the Early Triassic period. Approaching the end of the period, however, the therocephalians were in decline to eventual extinction, likely outcompeted by the rapidly diversifying Saurian lineage of diapsids , equipped with sophisticated respiratory systems better suited to
1519-465: The extinction event and thrived in the early Triassic. Dr. Elias Root Beadle, a Philadelphia missionary and avid fossil collector, discovered the first Lystrosaurus skull. Beadle wrote to the eminent paleontologist Othniel Charles Marsh , but received no reply. Marsh's rival, Edward Drinker Cope , was very interested in seeing the find, and described and named Lystrosaurus in the Proceedings of
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1568-471: The first of the cynodonts . Like all land animals, the therapsids were seriously affected by the Permian–Triassic extinction event , with the very successful gorgonopsians and the biarmosuchians dying out altogether and the remaining groups— dicynodonts , therocephalians and cynodonts —reduced to a handful of species each by the earliest Triassic . Surviving dicynodonts were represented by two families of disaster taxa ( Lystrosauridae and Myosauridae ),
1617-550: The fossils previously labeled as L. platyceps and L. oviceps as members of L. curvatus . L. maccaigi is the largest and apparently most specialized species, while L. curvatus was the least specialized. A Lystrosaurus -like fossil, Kwazulusaurus shakai , has also been found in South Africa. Although not assigned to the same genus , K. shakai is very similar to L. curvatus . Some paleontologists have therefore proposed that K. shakai
1666-630: The herbivorous Tapinocephalidae were classified as members of Anomodontia. Anomodontia includes the dicynodonts , a clade of tusked, beaked herbivores, and the most diverse and long-lived clade of non-cynodont therapsids. Other members of Anomodontia include Suminia , which is thought to have been a climbing form. Gorgonopsia is an abundant but morphologically homogeneous group of saber-toothed predators . It has been suggested that Therocephalia might not be monophyletic, with some species more closely related to cynodonts than others. However, most studies regard Therocephalia as monophyletic. Cynodonts are
1715-473: The hindlimbs, and the animal is thought to have been a powerful digger that nested in burrows. Lystrosaurus survived the Permian-Triassic extinction , 252 million years ago. In the Early Triassic , they were by far the most common terrestrial vertebrates, accounting for as many as 95% of the total individuals in some fossil beds. Researchers have offered various hypotheses for why Lystrosaurus survived
1764-499: The longest time. As so often with fossils, there is debate in the paleontological community as to exactly how many species have been found in the Karoo basin. Studies from the 1930s to 1970s suggested a large number (23 in one case). However, by the 1980s and 1990s, only 6 species were recognized in the Karoo : L. curvatus , L. platyceps , L. oviceps , L. maccaigi , L. murrayi , and L. declivis . A study in 2011 reduced that number to four, treating
1813-430: The mammaliaform Morganucodon suggest that even early mammaliaforms had reptile-like metabolic rates. Evidence for respiratory turbinates, which have been hypothesized to be indicative of endothermy, was reported in the therocephalian Glanosuchus , but subsequent study showed that the apparent attachment sites for turbinates may simply be the result of distortion of the skull. The evolution of integument in therapsids
1862-562: The most diverse and longest-lived of the therapsid groups, as Cynodontia includes mammals . Cynodonts are the only major therapsid clade to lack a Middle Permian fossil record, with the earliest-known cynodont being Charassognathus from the Wuchiapingian age of the Late Permian. Non-mammalian cynodonts include both carnivorous and herbivorous forms. [REDACTED] Eupelycosauria Too Many Requests If you report this error to
1911-508: The other four clades are controversial. The most widely accepted hypothesis of therapsid relationships, the Hopson and Barghausen paradigm, was first proposed in 1986. Under this hypothesis, biarmosuchians are the earliest-diverging major therapsid group, with the other five groups forming the Eutherapsida, and within Eutherapsida, gorgonopsians are the sister taxon of eutheriodonts, together forming
1960-459: The pineal foramen, and the foramen is completely absent in probainognathian cynodonts. Evidence from oxygen isotopes, which are correlated with body temperature, suggests that most Permian therapsids were ectotherms and that endothermy evolved convergently in dicynodonts and cynodonts near the end of the Permian. In contrast, evidence from histology suggests that endothermy is shared across Therapsida, whereas estimates of blood flow rate and lifespan in
2009-496: The presence of foramina on the snout of therocephalians and early cynodonts, but the arrangement of foramina in these taxa actually closely resembles lizards, which would make the presence of mammal-like whiskers unlikely. Therapsids evolved from a group of pelycosaurs called sphenacodonts . Therapsids became the dominant land animals in the Middle Permian , displacing the pelycosaurs. Therapsida consists of four major clades :
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2058-574: The sacral vertebrae are fused to each other and to the pelvis . A buttress above each acetabulum (hip socket) is thought to have prevented dislocation of the femur (thigh bone) while Lystrosaurus was walking with a semi-sprawling gait. The forelimbs of Lystrosaurus were massive, and Lystrosaurus is thought to have been a powerful burrower. Mummified specimens recovered from the Karoo Basin and described in 2022 revealed that Lystrosaurus had dimpled, leathery, and hairless skin. Lystrosaurus
2107-512: The scarcely known Kombuisia , and a single group of large stocky herbivores , the Kannemeyeriiformes , which were the only dicynodont lineage to thrive during the Triassic. They and the medium-sized cynodonts (including both carnivorous and herbivorous forms) flourished worldwide throughout the Early and Middle Triassic. They disappear from the fossil record across much of Pangea at the end of
2156-439: The sister taxon of Eutheriodontia, other studies have found dinocephalians and anomodonts to form a clade, and both the phylogenetic position and monophyly of Biarmosuchia remain controversial. In addition to the six major groups, there are several other lineages and species of uncertain classification. Raranimus from the early Middle Permian of China is likely to be the earliest-diverging known therapsid. Tetraceratops from
2205-415: The skull and took up a lot of space on the top and back of the skull. As a result, the eyes were set high and well forward on the skull, and the face was short. Features of the skeleton indicate that Lystrosaurus moved with a semi-sprawling gait . The lower rear corner of the scapula (shoulder blade) was strongly ossified (built of strong bone), which suggests that movement of the scapula contributed to
2254-420: The sprawling legs of reptiles and pelycosaurs. Also compared to these groups, the feet were more symmetrical, with the first and last toes short and the middle toes long, an indication that the foot's axis was placed parallel to that of the animal, not sprawling out sideways. This orientation would have given a more mammal -like gait than the lizard -like gait of the pelycosaurs. The physiology of therapsids
2303-435: The stride length of the forelimbs and reduced the sideways flexing of the body. The five sacral vertebrae were massive but not fused to each other and to the pelvis , making the back more rigid and reducing sideways flexing while the animal was walking. Therapsids with fewer than five sacral vertebrae are thought to have had sprawling limbs, like those of modern lizards. In dinosaurs and mammals , which have erect limbs,
2352-568: The very hot, dry and oxygen-poor world of the End-Triassic. Dicynodonts were among the most successful groups of therapsids during the Late Permian, and survived through to near the end of the Triassic. Mammals are the only living therapsids. The mammalian crown group , which evolved in the Early Jurassic period, radiated from a group of mammaliaforms that included the docodonts . The mammaliaforms themselves evolved from probainognathians ,
2401-424: Was possibly an ancestor of or closely related to the ancestors of L. curvatus , while L. maccaigi arose from a different lineage. L. maccaigi is found only in sediments from the Permian period, and apparently did not survive the Permian–Triassic extinction event . Its specialized features and sudden appearance in the fossil record without an obvious ancestor may indicate that it immigrated into
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