Pareiasaur

Pareiasaurs (meaning "cheek lizards") are an extinct group of anapsid reptiles classified in the family Pareiasauridae. They were large herbivores that flourished during the Permian period.

Description

Pareiasaurs ranged in size from 60 to 300 centimetres (2.0 to 9.8 ft) long, and may have weighed up to 600 kilograms (1,300 lb). They were stocky, with short tails, small heads, robust limbs, and broad feet. The cow-sized species Bunostegos, which lived 260 million years ago, is the earliest known example of a tetrapod with a fully erect posture as its legs were positioned directly under their bodies. Pareiasaurs were protected by bony scutes called osteoderms that were set into the skin. Their heavy skulls were ornamented with multiple knobs and ridges. The leaf-shaped multi-cusped teeth resemble those of iguanas, caseids, and other reptilian herbivores. This dentition, together with the deep body, which may have housed an extensive digestive tract, are evidence of a herbivorous diet. Most authors have assumed a terrestrial lifestyle for pareiasaurs, but bone microanatomy suggests a more aquatic, plausibly amphibious lifestyle.

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Permian

The Permian is a geologic period and system which extends from 298.9 to 252.17 million years ago. It is the last period of the Paleozoic, following the Carboniferous and preceding the Triassic of the Mesozoic. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the ancient kingdom of Permia.

The Permian witnessed the diversification of the early amniotes into the ancestral groups of the mammals, turtles, lepidosaurs and archosaurs. The world at the time was dominated by a single supercontinent known as Pangaea, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior.Amniotes, who could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors.

The Permian (along with the Paleozoic) ended with the largest mass extinction in Earth's history, in which nearly 90% of marine species and 70% of terrestrial species died out. It would take well into the Triassic for life to recover from this catastrophe. Recovery from the Permian-Triassic extinction event was protracted; on land, ecosystems took 30 million years to recover.