* They have mammary glands and nurse their young. This is a defining characteristic of mammals.
* They are warm-blooded. They regulate their own body temperature internally, unlike reptiles or amphibians.
* They have hair or fur covering their bodies. This helps insulate them and keep them warm.
* They breathe air with lungs. They are not aquatic creatures and rely on lungs for respiration.
* They give birth to live young. Unlike birds or reptiles, orangutans do not lay eggs.
* They possess a four-chambered heart. This is a common feature among mammals.
* They have a highly developed brain. Orangutans are highly intelligent and exhibit complex cognitive abilities.
These shared traits place orangutans firmly within the class Mammalia. They are part of the primate order, specifically within the Hominidae family alongside humans, chimpanzees, gorillas, and bonobos.