Final answer:
The most distinctive traits about the Neandertals' cold adaptation complex include a barrel-shaped chest, large nose, and short limbs, while their skeletal structure further suggests adaptation to harsh climates.
Step-by-step explanation:
The most distinctive traits about the cold adaptation complex of Neandertals include short limbs, a large nose, a barrel-shaped chest, and other skeletal characteristics. However, among these traits, the barrel-shaped chest is particularly noteworthy as it is directly related to their adaptation to cold climates. This chest shape would have helped in the thermoregulation of the body temperature in cold environments. Furthermore, Neandertals had a large nose which is thought to have warmed and humidified the cold air before it reached their lungs. Their robust body and limb structure also supported their lifestyle in harsh climates.
Additional skeletal features of Neandertals include a pronounced brow ridge, a large skull with an occipital bun, a robust humerus with a massive head suggesting the capability for throwing projectiles and using spears. They also had large incisors which often exhibited signs of wear, possibly due to non-feeding activities such as chewing on leather. These traits combined suggest that Neandertals were highly adapted for survival in cold environments.