According to evolutionary theory and the fossil record, which type of plant appeared just after this gymnosperm?

angiosperm

Explanation:

It was during the Devonian Period when gymnosperms evolved from the seed ferns

However, gymnosperm are plant species whose seeds are not confined in an ovary. For example - conifer

In the period of Mesozoic era , the scorpionflies ( species feeding on pollination drops) carried out pollination of gymnosperm and led to the coevolution of insects feeding on nectar which later on drove the evolution of angiosperms and also themselves.

Thus, it can be said the flowers and its pollinators evolved simultaneously.

hence, the answer is angiosperm.

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