The conditions for fossilization occur with lower frequency in terrestrial ecosystems compared to aquatic systems for example, so even though complex life originated in marine ecosystems, if there had been more terrestrial species than aquatic species, we would not necessarily expect to find this in fossilization as far as I know.

Plant evolution is something that is extremely interesting to me, and I liked that part of the graphic. The arms race in ecosystems (With the classic example being rainforests) driving biodiversity, and the evolution of plants from gymnosperms to angiosperms in response to this (among other factors) is fascinating!

it seems like it was always assumed to be a salt water creature, but it actually makes more sense in my head as a fresh water one, as it would pop into habitats conducive to terrestrial life