Final answer:
The evolutionary novelty of ornithopods is the (Option A) lower jaw joint located below the level of the tooth rows, allowing for complex chewing.
Step-by-step explanation:
The evolutionary novelties of ornithopods include A. lower jaw joint located below the level of the tooth rows. Ornithopods were a group of herbivorous dinosaurs that included duck-billed dinosaurs, among others. These dinosaurs exhibited a unique feature where their lower jaw joints were situated beneath the tooth rows, enabling more complex chewing motions necessary for processing plant materials. This adaptation helped ornithopods become some of the most successful herbivorous animals of their time.