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 period. 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 in sedimentary rocks, these pig-sized organisms were the most common mammal-like reptiles of the Permian.
Anatomically, what was true of Lystrosaurus?
A) Its jaw would have been hinged the same way as the jaws of the early reptiles were hinged.B) It was a tetrapod.
C) It had skin without scales, typical of modern amphibians.
D) It would have had no temporal fenestra in its skull.
Answer: B
How many of Lystrosaurus' features below can help explain why these organisms fossilized so abundantly?
I. the presence of hard parts, such as tusksII. its arid environment
III.its persistence across at least two geological eras
IV. its widespread geographic distribution
V. its mixture of reptilian and mammalian features
A) only one of these statements
B) two of these statements
C) three of these statements
D) four of these statements
E) all five of these statements
Answer: C
Which of the following is the most likely explanation for the modern-day distribution of dicynodont fossils? A) There had been two previous supercontinents that existed at different times long before the Permian period.
B) The dicynodonts were evenly distributed throughout all of Pangaea.C) The dicynodonts were distributed more abundantly throughout Gondwanaland than throughout any other land mass.
D) The dicynodonts were amphibious and able to swim long distances.
E) The dicynodonts could survive for periods of months aboard "rafts" of vegetation, few of which made their way to the northern hemisphere.
Answer: C
If an increase in dicynodont species diversity (in other words, number of species) occurred soon after the Permian extinction, and if it occurred for the same general reason usually given for the increase in mammalian diversity following the Cretaceous extinction, then it should be attributed to
A) an innovation among the dicynodonts that allowed them to fill brand-new niches.B) the availability of previously occupied niches.
C) the extinction of the dinosaurs (except the birds).
D) their outcompetition of many other terrestrial organisms.
Answer: B
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