We can represent atoms by listing the number of protons, neutrons, and electrons—for example, 2p+, 2n0, 2e- for helium. Which of the following represents the 18O isotope of oxygen?

#Question id: 4973

#Unit 11. Evolution and Behavior

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

#Question id: 4974

#Unit 11. Evolution and Behavior

Which of these is the most likely explanation for the modern-day distribution of dicynodont fossils?

#Question id: 4975

#Unit 11. Evolution and Behavior

The observation that tusks were limited to males in several species, and were apparently not used in food-gathering, is evidence that the tusks probably

#Question id: 4976

#Unit 11. Evolution and Behavior

Which of these is the most likely explanation for the existence of dicynodont fossils on modern-day Antarctica?

#Question id: 4977

#Unit 11. Evolution and Behavior

There are at least a dozen known species in the extinct genus Lystrosaurus. If each species was suited to a quite different environment, then this relatively large number of species is likely due to

#Question id: 4978

#Unit 11. Evolution and Behavior

The dicynodonts survived the mass extinction that was most closely correlated in time, if not in cause, with