Final answer:
No, that statement is False. Not all iguanodontids were large, heavily built ornithopods.
Step-by-step explanation:
No, that statement is False. Not all iguanodontids were large, heavily built ornithopods. While many iguanodontids were indeed large and heavily built, there were also smaller species within the group. For example, the Hypsilophodon was a smaller, lightly-built ornithopod that belonged to the iguanodontid family.