Final answer:
The movement of vertebrates from water to land had the greatest impact on Paleozoic food webs.
Step-by-step explanation:
The evolutionary change that would have had the greatest impact on Paleozoic food webs is the movement of vertebrates from water to land. This transition allowed vertebrates to access new food sources and escape predation. As plants became more common on land, vertebrates could feed on them directly or on the insects and other animals that relied on plants for food. This change in the food web led to the diversification and expansion of terrestrial ecosystems during the Paleozoic Era.