#Question id: 4973

Fossils of Lystrosaurus, a dicynodont therapsid, are most common in parts of modern-day South America, South Africa, Madagascar, India, South Australia, and Antarctica. It apparently lived in arid regions, and was mostly herbivorous. It originated during the mid-Permian period, survived the Permian extinction, and dwindled by the late Triassic, though there is evidence of a relict population in Australia during the Cretaceous. The dicynodonts had two large tusks, extending down from their upper jaws; the tusks were not used for food gathering, and in some species were limited to males. Food was gathered using an otherwise toothless beak. Judging from the fossil record, these pig-sized organisms were the most common mammal-like reptiles of the Permian.Which of Lystrosaurusʹ features help explain why these organisms fossilized so abundantly?

I. the presence of hard parts, such as tusks

II. its herbivorous diet

III. its persistence across at least two geological eras

IV. its widespread geographic distribution

V. its mixture of reptilian and mammalian features