Complex sentence: The first "Ginkgo" leaves were found during the Triassic period, but there were many species of "Ginkgo" during the Jurassic and Cretaceous periods as well.
Split into simpler sentences: The first "Ginkgo" leaves were found during the Triassic period. There were many species of "Ginkgo" during the Jurassic and Cretaceous periods as well.