题目选项分析

Fossilized teeth of an extinct species of herbivorous great ape have on them phytoliths, which are microscopic petrified remains of plants. Since only phytoliths from certain species of plants are found on the teeth, the apes' diet must have consisted only of those plants.

The argument assumes which one of the following?

【选项】None of the plant species that left phytoliths on the apes' teeth has since become extinct