Which of the following correctly describes the effect of climate on the evolution of vertebrates in the mesozoic?
a. temperatures increased across the permian-triassic boundary favoring the evolution of larger vertebrate fauna.
b. oxygen dropped across the permian-triassic boundary acting as a selective pressure for more efficient respiratory systems
c. carbon dioxide dropped across the permian-triassic boundary reducing the growth of plants which lowered food source availability.
d. the climate becomes more homogeneous in the permian than in the triassic slowing the rate of evolutionary change.