an innovation among the dicynodonts that allowed them to fill brand new niches. an innovation among the dicynodonts that allowed them to fill brand new niches. the availability of previously occupied niches. the availability of previously occupied niches. the extinction of the dinosaurs (except the birds). the extinction of the dinosaurs (except the birds)., the evolution of humans.

Complete question:

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 out-competition of many other terrestrial organisms.

B) the availability of previously occupied niches.

Explanation:              

Some species could survive massive extinctions caused by severe natural catastrophes. Some of them were small animals that could hide in certain places that were useful for their protection during the catastrophe. Those animals, that for instance, could hide underground, were able to avoid extreme temperatures and highly toxic gas concentrations caused by the phenomenon. Catastrophes caused severe damage to the Earth´s surface, causing the extinction of many other animal and vegetal species, causing changes in the morphology of the ground, and in temperature. Animals that could survive found themselves in a whole different place. Many niches were now available to be re-occupied. Survivers could specialize in different feeding strategies,  finding new different shelters, and developing new morphological characteristics that lead to a rapid diversification and speciation.