The answer to whether a possum has bones is an unequivocal yes. As a mammal, the possum (referring primarily to the North American Virginia opossum, Didelphis virginiana) is a vertebrate, meaning it possesses an internal skeleton made of bone. This bony framework places it within the Infraclass Marsupialia. The possum’s bony framework is highly adapted to support its semi-arboreal, nocturnal lifestyle, modified with unique features to suit its ecological niche.
Defining the Possum Skeleton
The possum’s skeleton follows the foundational design shared by all vertebrates, consisting of a protective skull, a central spinal column, a rib cage, and four limbs. The vertebral column provides the main axis of support and flexibility, allowing the possum to navigate complex environments like tree branches. The structure of the forelimbs and hindlimbs supports a plantigrade stance, meaning the animal walks with the soles of its feet flat on the ground.
The skull is relatively long and narrow, housing 50 teeth—more than any other North American mammal. This large dental formula includes incisors, canine teeth, and specialized molars adapted for its omnivorous diet of insects, small vertebrates, fruits, and carrion. The overall skeletal framework is built for generalist survival, providing strength for digging and agility for climbing. The non-fused radius and ulna bones in the forelimbs allow for pronation and supination, which are wrist-twisting movements beneficial for grasping and digging.
Unique Skeletal Traits of Marsupials
The possum’s skeleton is defined by features specific to the marsupial infraclass, most notably the presence of epipubic bones. These are a pair of long, slender bones that project forward from the pubic region of the pelvis and extend into the abdominal musculature. These structures are often colloquially called “marsupial bones.”
The primary function of the epipubic bones is to provide a rigid anchor point for the abdominal muscles, which is thought to assist in locomotion. They act as a lever system, helping to stiffen the trunk during movement and possibly aiding in the asymmetrical gait typical of marsupials during a fast walk or jog. In females, these bones provide structural support for the marsupium, or pouch, and the developing young within it.
The tail also exhibits a specialized skeletal arrangement, reflecting the possum’s need for climbing. The caudal vertebrae that form the nearly hairless tail are adapted to create a highly prehensile organ. This prehensile tail allows the possum to grasp branches and stabilize itself while climbing, effectively serving as a fifth limb. While the tail is strong enough to support the animal temporarily, the ability to hang by the tail for long periods is generally limited to juveniles.
Understanding Possum Flexibility and Thanatosis
The common question about whether possums have bones often stems from observing their remarkable flexibility and a specific defense mechanism. Possums are capable of contorting their bodies to an impressive degree, which is not due to a lack of bones but rather to loose joint articulations and strong, flexible musculature. This allows them to navigate tight spaces and awkward climbing routes with ease.
When severely threatened, the possum may engage in a defense behavior known as thanatosis, or tonic immobility, which is popularly called “playing possum.” This is an involuntary, stress-induced physiological response where the animal enters a temporary, death-like state. During thanatosis, the body goes limp, the eyes remain open, and the animal becomes temporarily unresponsive to external stimuli.
The physical appearance of the possum during this state—limp, relaxed, and motionless—can lead observers to mistakenly believe the animal lacks a rigid skeletal structure. This feigned death is accompanied by physiological changes, including a significant drop in heart and respiratory rates. The complete relaxation of the muscles and the resulting flaccid posture are what create the illusion of a boneless or injured animal, a strategy that often deters predators who prefer live prey.