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61-609: The name of the biozone refers to Lystrosaurus , a small to medium-sized dicynodont therapsid . It is characterized by the appearance of further Lystrosaurus subspecies which are confined to this biozone. Lystrosaurus maccaigi and Lystrosaurus curvatus are the only two species found outside the Lystrosaurus Assemblage Zone in Upper Permian deposits of the underlying Daptocephalus Assemblage Zone . The first fossils to be found in

122-610: A semi-sprawling gait . The forelimbs were even more robust than 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

183-480: A thin section using a method like the Gazzi-Dickinson Method . This yields the relative percentages of quartz, feldspar, and lithic grains and the amount of clay matrix. The composition of a sandstone can provide important information on the genesis of the sediments when used with a triangular Q uartz, F eldspar, L ithic fragment ( QFL diagrams ). However, geologist have not been able to agree on

244-623: 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

305-478: A sandstone goes through as the degree of kinetic processing of the sediments increases. Dott's (1964) sandstone classification scheme is one of many such schemes used by geologists for classifying sandstones. Dott's scheme is a modification of Gilbert's classification of silicate sandstones, and it incorporates R.L. Folk's dual textural and compositional maturity concepts into one classification system. The philosophy behind combining Gilbert's and R. L. Folk's schemes

366-462: A set of boundaries separating regions of the QFL triangle. Visual aids are diagrams that allow geologists to interpret different characteristics of a sandstone. For example, a QFL chart can be marked with a provenance model that shows the likely tectonic origin of sandstones with various compositions of framework grains. Likewise, the stage of textural maturity chart illustrates the different stages that

427-445: A twofold classification: Cement is what binds the siliciclastic framework grains together. Cement is a secondary mineral that forms after deposition and during burial of the sandstone. These cementing materials may be either silicate minerals or non-silicate minerals, such as calcite. Sandstone that becomes depleted of its cement binder through weathering gradually becomes friable and unstable. This process can be somewhat reversed by

488-517: 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

549-415: Is λίστρον lístron ‘tool for leveling or smoothing, shovel, spade, hoe’) 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

610-837: Is a distinction that can be recognized in the field . In turn, the distinction between an orthoquartzite and a metaquartzite is the onset of recrystallization of existing grains. The dividing line may be placed at the point where strained quartz grains begin to be replaced by new, unstrained, small quartz grains, producing a mortar texture that can be identified in thin sections under a polarizing microscope. With increasing grade of metamorphism, further recrystallization produces foam texture , characterized by polygonal grains meeting at triple junctions, and then porphyroblastic texture , characterized by coarse, irregular grains, including some larger grains ( porphyroblasts .) Sandstone has been used since prehistoric times for construction, decorative art works and tools. It has been widely employed around

671-451: Is a marked drop in species abundance in the Lystrosaurus Assemblage Zone due to ecological crises which followed the Permian-Triassic extinction event . However, this has not affected the abundance of vertebrate fossils found within this biozone . The most ubiquitous fossils found are different species of Lystrosaurus , the most commonly occurring being Lystrosaurus murrayi and Lystrosaurus declivis . Lystrosaurus maccaigi

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732-498: Is composed of quartz or feldspar , because they are the most resistant minerals to the weathering processes at the Earth's surface. Like uncemented sand , sandstone may be imparted any color by impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Because sandstone beds can form highly visible cliffs and other topographic features, certain colors of sandstone have become strongly identified with certain regions, such as

793-527: Is diagnostic of the Katberg Formation. The sandstones are interspersed by reddish-brown siltstones and mudstones which were deposited as silt sediments washed down the braided channels further down the Karoo Basin . The mudstones here often contain cracks which are infilled with sandstone . The domination of sandstone in the Lystrosaurus Assemblage Zone shows that the climate at

854-546: Is in addition a notable gap in coal deposits at this time as a result. Siltstone and mudstone outcrops are less common, with the majority of outcrops of these being found in the lower sections within the Palingkloof Member and in its uppermost section within the Burgersdorp Formation. Nodule conglomerates comprising pedogenic nodules and intrabasinal clasts are also found. There

915-523: Is likely formed during eogenesis. Deeper burial is accompanied by mesogenesis , during which most of the compaction and lithification takes place. Compaction takes place as the sand comes under increasing pressure from overlying sediments. Sediment grains move into more compact arrangements, ductile grains (such as mica grains) are deformed, and pore space is reduced. In addition to this physical compaction, chemical compaction may take place via pressure solution . Points of contact between grains are under

976-480: 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

1037-431: Is redeposited in the unstrained pore spaces. Mechanical compaction takes place primarily at depths less than 1,000 meters (3,300 ft). Chemical compaction continues to depths of 2,000 meters (6,600 ft), and most cementation takes place at depths of 2,000–5,000 meters (6,600–16,400 ft). Unroofing of buried sandstone is accompanied by telogenesis , the third and final stage of diagenesis. As erosion reduces

1098-443: Is that it is better able to "portray the continuous nature of textural variation from mudstone to arenite and from stable to unstable grain composition". Dott's classification scheme is based on the mineralogy of framework grains, and on the type of matrix present in between the framework grains. In this specific classification scheme, Dott has set the boundary between arenite and wackes at 15% matrix. In addition, Dott also breaks up

1159-980: Is the only species of Lystrosaurus not found in the biozone of its namesake. Lystrosaurus curvatus does appear in the lowermost section of the biozone, although it disappears at the contact between the Palingkloof Member of the Balfour Formation and the Katberg Formation. For this reason L. curvatus is used as an index fossil for outcrops of the Permian-Triassic boundary. In the lower Katberg Formation, complete and sometimes mummified articulated skeletons of L. murrayi and L. declivus are found in bonebeds containing several individuals. The bonebeds are almost always overlain by mudrock infilled with sandstone and capped by other coarse-grained sediments. This provides substantial geological and taphonomical evidence that these Lystrosaurus died near to dried up river channels , mummified in

1220-623: The Beaufort Group rocks that encompass the current eight biozones were discovered by Andrew Geddes Bain in 1856. However, it was not until 1892 that it was observed that the geological strata of the Beaufort Group could be differentiated based on their fossil taxa . The initial undertaking was done by Harry Govier Seeley who subdivided the Beaufort Group into three biozones , which he named (from oldest to youngest): These proposed biozones Seeley named were subdivided further by Robert Broom between 1906 and 1909. Broom proposed

1281-873: 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

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1342-690: 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

1403-599: 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

1464-444: The arid climate before their remains were buried by floods . The Permian-Triassic extinction event caused the extinction of all gorgonopsians and almost all dicynodont species except for Lystrosaurus and a select few other species such as Myosaurus gracilis . Therocephalian species experienced a Lilliput Effect where only smaller species survived and thrived after the extinction event. Moschorhinus , for example,

1525-450: 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

1586-611: 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

1647-595: 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

1708-482: 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

1769-526: 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

1830-715: The Triassic; complete ecological recovery took 30 million years, spanning the Early and Middle Triassic . Several attempts have been made to explain why Lystrosaurus survived the Permian–Triassic extinction event , the "mother of all mass extinctions", and why it dominated Early Triassic fauna to such an unprecedented extent: Sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains, cemented together by another mineral. Sandstones comprise about 20–25% of all sedimentary rocks . Most sandstone

1891-491: The application of tetraethyl orthosilicate (Si(OC 2 H 5 ) 4 ) which will deposit amorphous silicon dioxide between the sand grains. The reaction is as follows. Pore space includes the open spaces within a rock or a soil. The pore space in a rock has a direct relationship to the porosity and permeability of the rock. The porosity and permeability are directly influenced by the way the sand grains are packed together. Sandstones are typically classified by point-counting

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1952-436: The boundary reveal a change in the fluvial environment, from meandering high sinuosity river channels composed of greenish-grey siltstones and mudstones found in the underlying Daptocephalus Assemblage Zone . From the start of the Palingkloof Member the predominant presence of mudstone and siltstone show that meandering river channels were present, however, in arid and warmer conditions due to change in colour of

2013-473: The common minerals most resistant to weathering processes at the Earth's surface, as seen in the Goldich dissolution series . Framework grains can be classified into several different categories based on their mineral composition: Matrix is very fine material, which is present within interstitial pore space between the framework grains. The nature of the matrix within the interstitial pore space results in

2074-456: The depositional environment, older sand is buried by younger sediments, and it undergoes diagenesis . This mostly consists of compaction and lithification of the sand. Early stages of diagenesis, described as eogenesis , take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in the sands, with only slight compaction. The red hematite that gives red bed sandstones their color

2135-407: The depth of burial, renewed exposure to meteoric water produces additional changes to the sandstone, such as dissolution of some of the cement to produce secondary porosity . Framework grains are sand-sized (0.0625-to-2-millimeter (0.00246 to 0.07874 in) diameter) detrital fragments that make up the bulk of a sandstone. Most framework grains are composed of quartz or feldspar , which are

2196-446: The different types of framework grains that can be present in a sandstone into three major categories: quartz, feldspar, and lithic grains. When sandstone is subjected to the great heat and pressure associated with regional metamorphism , the individual quartz grains recrystallize, along with the former cementing material, to form the metamorphic rock called quartzite . Most or all of the original texture and sedimentary structures of

2257-485: The earliest ancestors of Archosauria appear in the Lystrosaurus zone. These species are known as archosauromorphs and archosauriformes . Examples of these are Prolacerta broomi and Proterosuchus fergusi respectively found in the lower Lystrosaurus Assemblage Zone. A variety of ichnofossils are also found, especially burrow casts left by Lystrosaurus . The deep-bodied ray-finned fish Caruichthys

2318-471: 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

2379-618: The first third of the Burgersdorp Formation east of 24°E. The Balfour Formation is located within the Adelaide Subgroup, while the Katberg and Burgersdorp are within the Tarkastad Subgroup of the Beaufort Group . Its contact with the underlying Daptocephalus Assemblage Zone marks the Permian - Triassic boundary. The boundary is defined by a change in the sedimentary rock types. The changing rock types across

2440-411: The following biozones (from oldest to youngest): These biozone divisions were approved by paleontologists of the time and were left largely unchanged for several decades. The Lystrosaurus Assemblage Zone was first named by Robert Broom in 1906. Initially Broom had subdivided the existing Lystrosaurus zone into the Lystrosaurus and Procolophon Assemblage Zones respectively. The biozone

2501-556: 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

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2562-464: The greatest diversification with species such as Thrinaxodon liorhinus and Galesaurus planiceps being found. In the upper Katberg and the lower Burgersdorp Formations more derived cynodonts , the Eucynodontia , make an appearance. Small procolonphonoid parareptiles such as Owenetta kitchingorum and Procolophon trigoniceps , and temnospondyl amphibians are also found. In addition,

2623-433: The greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. Pressure solution contributes to cementing, as the mineral dissolved from strained contact points

2684-442: The hardness of individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones , for sharpening blades and other implements. Non-friable sandstone can be used to make grindstones for grinding grain, e.g., gritstone . A type of pure quartz sandstone, orthoquartzite, with more of 90–95 percent of quartz, has been proposed for nomination to

2745-499: 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

2806-493: The much lower temperatures and pressures associated with diagenesis of sedimentary rock, but diagenesis has cemented the rock so thoroughly that microscopic examination is necessary to distinguish it from metamorphic quartzite. The term orthoquartzite is used to distinguish such sedimentary rock from metaquartzite produced by metamorphism. By extension, the term orthoquartzite has occasionally been more generally applied to any quartz-cemented quartz arenite . Orthoquartzite (in

2867-464: The narrow sense) is often 99% SiO 2 with only very minor amounts of iron oxide and trace resistant minerals such as zircon , rutile and magnetite . Although few fossils are normally present, the original texture and sedimentary structures are preserved. The typical distinction between a true orthoquartzite and an ordinary quartz sandstone is that an orthoquartzite is so highly cemented that it will fracture across grains, not around them. This

2928-458: The number of species was thought to be much higher. They ranged in size from that of 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

2989-638: The product of physical and chemical weathering of bedrock. Weathering and erosion are most rapid in areas of high relief, such as volcanic arcs , areas of continental rifting , and orogenic belts . Eroded sand is transported by rivers or by the wind from its source areas to depositional environments where tectonics has created accommodation space for sediments to accumulate. Forearc basins tend to accumulate sand rich in lithic grains and plagioclase . Intracontinental basins and grabens along continental margins are also common environments for deposition of sand. As sediments continue to accumulate in

3050-712: The red rock deserts of Arches National Park and other areas of the American Southwest . Rock formations composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs . Quartz-bearing sandstone can be changed into quartzite through metamorphism , usually related to tectonic compression within orogenic belts . Sandstones are clastic in origin (as opposed to either organic , like chalk and coal , or chemical , like gypsum and jasper ). The silicate sand grains from which they form are

3111-454: The rocks to reddish-brown and maroon. These are inter-spaced with claystones , olive to grey fine-grained sandstone , and reddish-brown to maroon shales . In the overlying Katberg Formation, alluvial fans containing braided low sinuosity river channels comprising mainly coarse-grained sandstone appear. These sandstones form either single and multi-storey channel sandstones and crevasse-splay sandstones . The dominance of sandstones

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3172-580: 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

3233-417: The sandstone are erased by the metamorphism. The grains are so tightly interlocked that when the rock is broken, it fractures through the grains to form an irregular or conchoidal fracture. Geologists had recognized by 1941 that some rocks show the macroscopic characteristics of quartzite, even though they have not undergone metamorphism at high pressure and temperature. These rocks have been subject only to

3294-415: 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

3355-435: 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,

3416-415: The time had become more arid , where rainfall was unpredictable and the shallow, braided rivers would seasonally dry up. When the rivers flowed again after the rains, due to being shallow, they would frequently flood their banks, hence the presence of crevasse-splays . Conglomerates are also found in eastern outcrops, which are indicative of erosion occurring due to die-offs of plant ecosystems . There

3477-626: The world in constructing temples, churches, homes and other buildings, and in civil engineering . Although its resistance to weathering varies, sandstone is easy to work. That makes it a common building and paving material, including in asphalt concrete . However, some types that have been used in the past, such as the Collyhurst sandstone used in North West England , have had poor long-term weather resistance, necessitating repair and replacement in older buildings. Because of

3538-910: Was also found in layers of this biozone. The Lystrosaurus Assemblage Zone dates to approximately 251 to 249 Ma, and correlates with the Kopanskaya and Staritskaya Formations of Russia, and with the Jiucaiyuan Formation of China, the Knocklofty and Arcadia Formations of Australia, the Buena Vista Formation of the Paraná Basin , South America, and the Panchet Formation of India. Lystrosaurus Lystrosaurus ( / ˌ l ɪ s t r oʊ ˈ s ɔːr ə s / ; 'shovel lizard'; proper Greek

3599-544: Was later revised in 1976 by James Kitching where Kitching assimilated the Procolophon zone into the Lystrosaurus zone due to discovering that fossils of the small parareptile Procolophon were likewise found throughout the Lystrosaurus zone. The Lystrosaurus Assemblage Zone ranges from the Palingkloof Member of the upper Balfour Formation west of 24°E. It comprises the entire Katberg Formation and

3660-462: Was one of the larger therocephalians to survive the initial extinction event, however, fossil occurrences of this species cease above the lower Katberg Formation. This is also true of Lystrosaurus where only the smaller species thrived in the Triassic . By the upper sections of the biozone, ecological niches began to recover as evidenced by the appearance of new species. Cynodonts experienced

3721-424: 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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