Final answer:
The distinctive feature of ornithischian dinosaurs is B. a toothless predentary, part of a beak-like structure for feeding, despite their 'bird-hipped' pelvis not being an ancestral trait to modern birds.
Step-by-step explanation:
The distinctive features of ornithischian dinosaurs include a toothless predentary that formed part of a beak-like structure useful for clipping or cropping vegetation. Ornithischians are known as "bird-hipped" dinosaurs due to the superficial similarity in the structure of their pelvis to that of modern birds, although birds actually evolved from the saurischian "lizard-hipped" dinosaurs. Option C, a toothless predentary, is the correct answer for the distinctive feature of ornithischian dinosaurs.
The distinctive features of ornithischian dinosaurs include a triradiate pelvis and a toothless predentary.
A triradiate pelvis is a unique feature of ornithischian dinosaurs where the hip bones are fused to form a Y-shaped structure. This pelvis structure is similar to the pelvis of birds.
A toothless predentary is a bone in front of the lower jaw that lacks teeth, and it is found in some ornithischian dinosaurs. This adaptation is also seen in modern birds where the lower jaw is toothless.