Lystrosaurus

***Lystrosaurus*** (meaning "shovel lizard" in Greek) is an extinct genus of dicynodont therapsid that lived during the Late Permian and Early Triassic periods, around 250 million years ago in what is now Antarctica, India and South Africa. At present 4 to 6 species are recognized, although from the 1930s to 1970s the number of species was thought to be much higher. *Lystrosaurus* had only two teeth, as with all other dicynodonts, as well as a pair of tusk-like canines. *Lystrosaurus* 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*.

## Description

*Lystrosaurus* was a pig-sized dicynodont therapsid, typically about 3 feet (0.91 m) long and weighing about 200 pounds (91 kg). 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 beaks 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. The lower jaw was able to slide backwards and forwards to a remarkable degree, enabling the animal to move vegetation into its mouth. It used its tusks to dig up roots and tubers, which also formed part of its diet. The nostrils of *Lystrosaurus* were high up on its deeply curved snout, enabling it to feed in the shallow water of its swamp and marsh habitat.

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 dinosaurs and mammals, 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.

## Paleoecology

*Lystrosaurus* 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 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* 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

## Death and Extinction

Eaten by predators like Cynodonts, Gorgonopsids, and *Proterosuchus* that went extinct in the Permian. The early Triassic Extinction finaly killed this animal. However before that it may have made up half of life on earth.

## Appearance in other media

### *Jurassic Park*

* Recently, it has been confirmed to appear in Jurassic World: Dominion as the first dicynodont to appear in the franchise.

## References

1. ↑ Template:Cite web
2. ↑ Template:Cite book
3. ↑ *Lystrosaurus* MSN Encarta encyclopedia.
4. ↑ 4.0 4.1 4.2 4.3 Cite error: Invalid `<ref>` tag; no text was provided for refs named `SurkovKalandadzeBenton2005LystrosaurusGeorgi`
5. ↑ Template:Cite book
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