Lystrosaurus
Encyclopedia
Lystrosaurus was a genus
of Late Permian
and Early Triassic
Period dicynodont
therapsids, which lived around 250 million years ago in what is now Antarctica, India
, 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.
Being 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, approximately the size of a pig
. The structure of its shoulders and hip joints suggest that Lystrosaurus moved with 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 was by far the most common terrestrial vertebrate of the Early Triassic
, accounting for as many as 95% of the total individuals in some fossil beds. It has often been suggested that it had anatomical features that enabled it to adapt better than most animals to the atmospheric conditions that were created by the Permian–Triassic extinction event and which persisted through the Early Triassic—low concentrations of oxygen
and high concentrations of carbon dioxide
. However recent research suggests that these features were no more pronounced in Lystrosaurus than in genera that perished in the extinction or genera that survived but were much less abundant than Lystrosaurus.
-sized dicynodont
therapsid, typically about 3 foot (0.9144 m) long and weighing about 200 pound. Unlike other therapsids, dicynodonts had very short snouts and no teeth except for the tusk
-like upper canines. Dicynodonts are generally thought to have had horny
beak
s like those of turtles, for shearing off pieces of vegetation which were then ground on a horny secondary palate
when the mouth was closed. 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 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 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 dinosaur
s and mammal
s, which have erect limbs, 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.
Lystrosaurus fossils have been found in many late Permian
and Early Triassic
terrestrial bone bed
s, most abundantly in Africa, and to 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).
region, which is mostly in South Africa
; these specimens offer the best prospects of identifying species because they are the most numerous and have been studied for 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. Studies from the 1930s to 1970s suggested a large number (23 in one case). However, by the 1980s and 1990s, only six 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 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 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 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 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 Permian sediments.
Lystrosaurus georgi fossils have been found in the Earliest Triassic sediments of 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.
, 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 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.
by Edwin H. Colbert and his team in 1969–70 helped confirm the theory of plate tectonics
and convince the last of the doubters, since Lystrosaurus had already been found in the lower Triassic of southern Africa as well as in India and China.
for millions of years. At least one unidentified species of this genus survived the end-Permian mass extinction and, in the absence of predators and of 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 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 therocephalia
ns Tetracynodon
, Moschorhinus
and Ictidosuchoides
—but do not appear to have been abundant in 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:
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of Late Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
and Early Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
Period dicynodont
Dicynodont
Dicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...
therapsids, which lived around 250 million years ago in what is now Antarctica, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. Four to six species are currently recognized, although from the 1930s to 1970s the number of species was thought to be much higher.
Being a dicynodont
Dicynodont
Dicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...
, Lystrosaurus had only two teeth, a pair of tusk
Tusk
Tusks are elongated, continuously growing front teeth, usually but not always in pairs, that protrude well beyond the mouth of certain mammal species. They are most commonly canines, as with warthogs, wild boar, and walruses, or, in the case of elephants and narwhals, elongated incisors...
-like canines
Canine tooth
In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...
, and is thought to have had a horny beak that was used for biting off pieces of vegetation. Lystrosaurus was a heavily-built, herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
animal, approximately the size of a pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
. The structure of its shoulders and hip joints suggest that Lystrosaurus moved with 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 was by far the most common terrestrial vertebrate of the Early Triassic
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
, accounting for as many as 95% of the total individuals in some fossil beds. It has often been suggested that it had anatomical features that enabled it to adapt better than most animals to the atmospheric conditions that were created by the Permian–Triassic extinction event and which persisted through the Early Triassic—low concentrations of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and high concentrations of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. However recent research suggests that these features were no more pronounced in Lystrosaurus than in genera that perished in the extinction or genera that survived but were much less abundant than Lystrosaurus.
Description
Lystrosaurus was a pigPig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
-sized dicynodont
Dicynodont
Dicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...
therapsid, typically about 3 foot (0.9144 m) long and weighing about 200 pound. Unlike other therapsids, dicynodonts had very short snouts and no teeth except for the tusk
Tusk
Tusks are elongated, continuously growing front teeth, usually but not always in pairs, that protrude well beyond the mouth of certain mammal species. They are most commonly canines, as with warthogs, wild boar, and walruses, or, in the case of elephants and narwhals, elongated incisors...
-like upper canines. Dicynodonts are generally thought to have had horny
Horn (anatomy)
A horn is a pointed projection of the skin on the head of various animals, consisting of a covering of horn surrounding a core of living bone. True horns are found mainly among the ruminant artiodactyls, in the families Antilocapridae and Bovidae...
beak
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
s like those of turtles, for shearing off pieces of vegetation which were then ground on a horny secondary palate
Secondary palate
The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates.In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medially and their mutual fusion in the midline...
when the mouth was closed. 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 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.
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
(shoulder blade) was strongly ossified (built of strong bone), which suggests that movement of the scapula contributed to 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
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
, making the back more rigid and reducing sideways flexing while the animal was walking. Therapsids
Therapsida
Therapsida is a group of the most advanced synapsids, and include the ancestors of mammals. Many of the traits today seen as unique to mammals had their origin within early therapsids, including hair, lactation, and an erect posture. The earliest fossil attributed to Therapsida is believed to be...
with fewer than five sacral vertebrae are thought to have had sprawling limbs, like those of modern lizards. In dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s and mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, which have erect limbs, the sacral vertebrae are fused to each other and to the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
. A buttress above each acetabulum (hip socket) is thought to have prevented dislocation of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
(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.
Distribution and species
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
and Early Triassic
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
terrestrial bone bed
Bone bed
A bone bed is any geological stratum or deposit that contains bones of whatever kind. Inevitably, such deposits are sedimentary in nature. Not a formal term, it tends to be used more to describe especially dense collections...
s, most abundantly in Africa, and to 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).
Species found in Africa
Most Lystrosaurus fossils have been found in the Balfour and Katburg Formations of the KarooKaroo
The Karoo is a semi-desert region of South Africa. It has two main sub-regions - the Great Karoo in the north and the Little Karoo in the south. The 'High' Karoo is one of the distinct physiographic provinces of the larger South African Platform division.-Great Karoo:The Great Karoo has an area of...
region, which is mostly in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
; these specimens offer the best prospects of identifying species because they are the most numerous and have been studied for the longest time. As so often with fossils, there is debate in the paleontological community
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
as to exactly how many species have been found in the Karoo. Studies from the 1930s to 1970s suggested a large number (23 in one case). However, by the 1980s and 1990s, only six 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 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
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
, K. shakai is very similar to L. curvatus. Some paleontologists have therefore proposed that K. shakai 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
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "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 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
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
and Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
periods. A skull identified as L. curvatus has been found in late Permian sediments from Zambia
Zambia
Zambia , officially the Republic of Zambia, is a landlocked country in Southern Africa. The neighbouring countries are the Democratic Republic of the Congo to the north, Tanzania to the north-east, Malawi to the east, Mozambique, Zimbabwe, Botswana and Namibia to the south, and Angola to the west....
. For many years it had been thought that there were no Permian specimens of L. curvatus in 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 Permian sediments.
Other species
Moscow
Moscow is the capital, the most populous city, and the most populous federal subject of Russia. The city is a major political, economic, cultural, scientific, religious, financial, educational, and transportation centre of Russia and the continent...
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.
History
Dr. Elias Root Beadle, a Philadelphia missionary and avid fossil collector, discovered the first Lystrosaurus skull. Beadle wrote to the eminent paleontologist Othniel Charles MarshOthniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
, but received no reply. Marsh's rival, Edward Drinker Cope
Edward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...
, was very interested in seeing the find, and described and named Lystrosaurus in the Proceedings of the American Philosophical Society in 1870. Its name is derived from the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean 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.
Plate tectonics
The discovery of Lystrosaurus fossils at Coalsack Bluff in the Transantarctic MountainsTransantarctic Mountains
The three largest mountain ranges on the Antarctic continent are the Transantarctic Mountains , the West Antarctica Ranges, and the East Antarctica Ranges. The Transantarctic Mountains compose a mountain range in Antarctica which extend, with some interruptions, across the continent from Cape Adare...
by Edwin H. Colbert and his team in 1969–70 helped confirm the theory of plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
and convince the last of the doubters, since Lystrosaurus had already been found in the lower Triassic of southern Africa as well as in India and China.
Dominance of the Early Triassic
Lystrosaurus is notable for dominating southern Pangea during the Early TriassicEarly Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
for millions of years. At least one unidentified species of this genus survived the end-Permian mass extinction and, in the absence of predators and of herbivorous competitors, went on to thrive and re-radiate
Evolutionary radiation
An evolutionary radiation is an increase in taxonomic diversity or morphological disparity, due to adaptive change or the opening of ecospace. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment,...
into a number of species within the genus, becoming the most common group of terrestrial vertebrates during the Early Triassic; for 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 therocephalia
Therocephalia
Therocephalians are an extinct suborder of carnivorous eutheriodont therapsids that lived from the middle and late Permian into the Triassic 265.0—245.0 Ma existing for approximately ....
ns Tetracynodon
Tetracynodon
Tetracynodon is an extinct genus of therocephalian....
, Moschorhinus
Moschorhinus
Moschorhinus is an extinct genus of therocephalian. It was a carnivorous quadruped and lived in the Permian period. Described by South African paleontologist Robert Broom in 1920, its name is derived from the Ancient Greek words moschos "calf" and rhino- "nose".thumb|left|HeadIts short strong skull...
and Ictidosuchoides
Ictidosuchoides
Ictidosuchoides is an extinct genus of ictidosuchid therocephalian. Fossils have been found from the Karoo Basin in South Africa. The genus is known to have been one of the few therocephalians to have survived the Permian-Triassic extinction event in this area, although its numbers were quite low...
—but do not appear to have been abundant in the Triassic; complete ecological recovery took 30 million years, spanning the Early
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
and Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
.
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:
- One of the more recent theories is that the Permian–Triassic extinction event reduced the atmosphere's oxygen content and increased its carbon dioxideCarbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
content, so that many terrestrial species died out because they found breathing too difficult. It has therefore been suggested that Lystrosaurus survived and became dominant because its burrowing life-style made it able to cope with an atmosphere of "stale air", and that specific features of its anatomy were part of this adaptation: a barrel chest that accommodated large lungs, short internal nostrilNostrilA nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s that facilitated rapid breathing, and high neural spines (projections on the dorsal side of the vertebrae) that gave greater leverage to the muscles that expanded and contracted its chest. However, there are weaknesses in all these points: the chest of Lystrosaurus was not significantly larger in proportion to its size than in other dicynodontDicynodontDicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...
s that became extinct; although Triassic dicynodonts appear to have had longer neural spines than their Permian counter-parts, this feature may be related to posture, locomotion or even body size rather than respiratory efficiency; L. murrayi and L. declivis are much more abundant than other Early Triassic burrowers such as ProcolophonProcolophonProcolophon was a genus of lizard-like procolophonid reptiles with at least eight species that persisted through the Permian–Triassic extinction event, but became extinct in the later Triassic....
or ThrinaxodonThrinaxodonThrinaxodon was a cynodont, an ermine-sized therapsid. Pits on the skull suggest that Thrinaxodon may have had whiskers, and by extension a protective covering of fur. There are suggestions that it was warm-blooded...
.
- The suggestion that Lystrosaurus was helped to survive and dominate by being semi-aquatic has a similar weakness: although amphibianAmphibianAmphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s become more abundant in the Karoo's Triassic sediments, they were much less numerous than L. murrayi and L. declivis. - The most specialized and the largest animals are at higher risk in mass extinctions; this may explain why the unspecialized L. curvatus survived while the larger and more specialized L. maccaigi perished along with all the other large Permian herbivores and carnivores. Although Lystrosaurus generally looks adapted to feed on plants similar to DicroidiumDicroidiumDicroidium is an extinct genus of fork-leaved seed ferns that were distributed over Gondwana during the Triassic . Their fossils are known from South Africa, Australia, New Zealand, South America and Antarctica...
, which dominated the Early Triassic, the larger size of L. maccaigi may have forced it to rely on the larger members of the GlossopterisGlossopterisGlossopteris is the largest and best-known genus of the extinct order of seed ferns known as Glossopteridales ....
flora, which did not survive the end-Permian extinction. - Only the 1.5 metres (4.9 ft)–long therocephalian MoschorhinusMoschorhinusMoschorhinus is an extinct genus of therocephalian. It was a carnivorous quadruped and lived in the Permian period. Described by South African paleontologist Robert Broom in 1920, its name is derived from the Ancient Greek words moschos "calf" and rhino- "nose".thumb|left|HeadIts short strong skull...
and the large archosauriform ProterosuchusProterosuchusProterosuchus is an extinct genus of Early Triassic proterosuchid archosaur. Remains have been found from South Africa and China. The genus Chasmatosaurus is considered a junior synonym of Proterosuchus, as all species of Chasmatosaurus, including C. aleandri, C. vanhoepeni, and C. yuani, have...
appear large enough to have preyed on the Triassic Lystrosaurus species, and this shortage of predators may have been responsible for a Lystrosaurus population boom in the Early Triassic. - Perhaps the survival of Lystrosaurus was simply a matter of luck.
In popular culture
- Lystrosaurus was mentioned in BBCBBCThe British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
s 2002 documentary The Day The Earth Nearly DiedThe Day The Earth Nearly DiedThe Day The Earth Nearly Died is a British documentary produced by BBC in 2002. The program focuses on the mystery of the Permian extinction, which scientists believe killed over 90% of all life on earth at the end of the Permian, supposedly some 250 million years ago...
, a program which discuss the Permian extinction. In the program, the narrator says that Lystrosaurus was one of the therapsids which survived the extinction, and that it was the ancestor to all mammals, even humans. This is not correct, as paleontologists don't regard dicynodonta as ancestral to mammals. - Lystrosaurus appeared in the Impossible PicturesImpossible PicturesImpossible Pictures Ltd. is a London-based independent TV production company founded in 2002 by Tim Haines, creator of Walking with Dinosaurs and Jasper James....
production Walking with MonstersWalking with MonstersWalking with Monsters is a three-part British documentary film series about life in the Paleozoic, bringing to life extinct arthropods, fish, amphibians, synapsids, and reptiles...
. Here, it was shown evolving from the little dicynodontDicynodontDicynodontia is a taxon of anomodont therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'...
DiictodonDiictodonDiictodon was a genus of therapsid, roughly 45 cm long. It belonged to the sub-group Dicynodontia. These mammal-like synapsids lived during the Late Permian period, approximately 255 million years ago. Fossils have been found in Africa and Asia...
, even though both species lived at the same time. - Lystrosaurus also appeared in the 5th episode of Animal ArmageddonAnimal ArmageddonAnimal Armageddon is an American paleontology-based documentary television miniseries that originally aired from to on Animal Planet. All the prehistoric scenes are created 100% in Lightwave...
, "explaining" that the different Lystrosaurus species had interbred with each other to adapt better and to survive during the transition from Permian to Triassic.