Did the First Plants Prefer the Same Temperatures as Today's Plants? Evidence of Ordovician and Silurian Cryptospores, Trilete Spores and Graptolites

The species diversity during the Ordovician reached its maximum in the late Katian, which corresponds with a decrease in temperature. Vascular land plants, the parent plants of trilete spores, first reached a maximum after the Homerian glaciation. The Silurian graptolite species diversity is the reverse to that of the trilete spore diversity, i.e., the minimum of graptolite diversity usually corresponds with the maximum of trilete spore species. It can correspond to global climate regimes and the associated changes in the ocean ecosystem. The first cryptospores and trilete spores appeared in cold climatic areas during the Ordovician Period which does not support the hypothesis that tropical areas were a cradle for early plants. The average temperature in today's tropical belt, which has the greatest number of species, is similar to the average temperature in the Ordovician and Silurian temperate zones. Therefore, it is reasonable to suppose that, during these periods, plants preferred comparable temperatures to those in today's tropical belt.