In his book Metazoa, Peter Godfrey-Smith mentions that life in the ocean was more diverse than life on land, until a 130 million years ago, when diversity on land became exceptional, mostly driven by a feedback loop between insects and plants, as plant diversity allowed insect specialization and insect diversity allowed plant specialization. (Until finally we arrived at a situation where every species of fig tree had a specialized species of wasp responsible for pollinating that species of fig tree.)
https://www.amazon.com/Metazoa-Animal-Life-Birth-Mind-ebook/...