Final answer:
Gorillas and chimpanzees primarily use knuckle-walking, a type of quadrupedalism, for ground locomotion.
Step-by-step explanation:
Gorillas and chimpanzees on the ground use a form of locomotion known as knuckle-walking. When moving quadrupedally, apes like gorillas and chimpanzees support their weight on their knuckles, contrasting with monkeys that walk on their palms. This knuckle-walking is a distinctive form of quadrupedalism seen in these primates. Both species also display remarkable abilities to utilize tools and show insightful problem-solving, indicating a high level of intelligence.