Biology

Anatomy

First and foremost, Orangutans are famous for their auburn red hair. Fully developed adult males can weigh up to 200lbs, while females can weigh 110lbs. Ancient orangutans were twice the size of the kin that we know today. Orangutans started to shrink around 400,000 years ago when the earth began to cool. Their arms are the longest out of the great apes, enabling them to live amongst treetops, rarely treading ground. The arboreal ancestors or "tree-dwellers" that came before orangutans passed down limbs best suited for brachiation- swinging and climbing from tree to tree. Some examples of the adaptation in anatomy are a rotating shoulder joint, thumbs and big toes that have a great distance from the other digits (excluding humans), and stereoscopic vision which allows depth perception necessary for gauging distances. The most notable anatomical feature of male Bornean Orangutans is the flared cheek flaps and throat pouch that grow as the great ape ages.

Skull: A skull is a bone that forms in the head of vertebrates and protects the brain.

Face: black face and eyes. Older males will grow a beard.

Cheeks: Flanged in sexually mature males.

Throat: Sexually mature males will form a pendulous throat sack.

Arms: Orangutans have an arm span of about 7.5 feet, fingertip to fingertip.

Hands: Five fingers used for grasping and swinging.

Hips: High mobility with a full rotation of their joints, allowing the legs to move at almost any angle.

Legs: proportionately short legs compared to the arms.

Feet: Has five toes that can hold onto items while swinging from tree to tree or grab hold of branches for support.

Body: Covered in reddish-orange fur.

Physiology

Digestive System

Orangutans are omnivores but classified as frugivores due to their preference for fruit when its available. Their diet consists of fruit, seeds, nuts, berries, leaves, tree bark, flowers, insects, and bird eggs. All great apes (bonobos, chimpanzees, gorillas, orangutans) and humans share a similar digestive system: an oral cavity, esophagus, stomach, small intestine, large intestine, rectum, and anus. In contrast to the great apes, the small intestine can be 19ft long in humans, taking up the most space in our gut, whereas the large intestine takes up the most gut volume in great apes. This difference in gut anatomy gives great apes the ability to ferment incredible quantities of fiber from which they acquire and store outstanding amounts of energy.

Musculoskeletal System

Staying above ground in the treetops, the skeleton of an orangutan adapted to perfect this lifestyle relative to other primates who moved to the ground and acquired a different set of adaptations for their new home. For instance, an Orangutan's arm span is longer than its height, with a great space of 7.5 feet from fingertip to fingertip. Its thumbs and big toes are farther apart from other digits, and the proximal and middle phalanges of orangutans are more curved. Compared to other apes, orangutans have the most extended snout, and they have 32 teeth, just like a human!

Nervous System

The brain of an Orangutan weighs approximately 1lb and contains around 32 billion neurons. The occipital lobe correlates to vision, and orangutans have extraordinary eyesight, depth perception, and color vision. Primates have forward-facing eyes rather than one on each side of the head, providing binocular vision. Primates have a skeletal structure known as a postorbital closure, forming a bony cup around each eye.

Reproductive System

Orangutans sexually reproduce to conceive offspring, and those offspring have 48 diploid chromosomes. A female orangutan's reproductive stage is roughly nine months, and their reproductive cycle is about 30 days. Orangutans can live 35-40 years in the wild and 50 in captivity. A female orangutan (XX) gives birth to offspring, typically one at a time. She raises her young until it is approximately six to eight years old, thus giving orangutans low birth numbers due to the gap from when a female conceives again. The mother teaches her young everything it needs to know to survive independently. Mother and baby orangutans share a deep connection.

An adult male orangutan is intolerable to other males and will fight each other for control of mates and territory. Males become sexually mature at age 15, and they develop protruding cheek pads, a throat pouch, and grow long fur. Females prefer these characteristics in males and stay close to them for protection and fitness. Studies show that a new adaptation is growing among males, arrested development, which means that the males remain unflanged even after reaching sexual maturity. This unique characteristic makes larger flanged males less likely to attack the unflanged males because they assume they are still adolescents.

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