What is a defining characteristic of old world monkeys as opposed to new world monkeys?

A defining characteristic of Old World monkeys is the presence of non-prehensile tails, which contrasts sharply with many New World monkeys that possess prehensile tails. Non-prehensile tails in Old World monkeys are typically just for balance and support rather than for grasping and manipulation. This difference is largely due to the adaptations these two groups have evolved based on their environments and lifestyles.

New World monkeys, found primarily in Central and South America, often have prehensile tails that allow them to grasp branches and navigate their arboreal habitats effectively. In contrast, Old World monkeys, native to Africa and Asia, usually have tails that are not capable of gripping and instead are shorter or less flexible.

The other options, while they may pertain to specific variations or traits within either group, do not represent a defining characteristic that distinguishes Old World monkeys from New World monkeys as clearly as tail morphology does.