Possums and opossums are small to medium-sized marsupials with a set of physical features that make them easy to identify once you know what to look for: a pointed, pale face with dark eyes, a long naked tail, coarse grayish fur, and a body roughly the size of a house cat. But these animals are far more varied and physically interesting than a quick glimpse by a trash can might suggest. The term “possum” is used loosely in North America to mean the Virginia opossum, while in Australia and nearby regions it refers to an entirely different group of marsupials. Both branches share some traits and diverge wildly on others.
Face, Snout, and Whiskers
The Virginia opossum has one of the most recognizable faces in North American wildlife. Its snout is long, narrow, and pinkish, tapering to a pointed nose that gives the animal an almost rat-like profile. The eyes are small, round, and dark, set against pale whitish or grayish fur on the face. Ears are thin, hairless, and black, sometimes tipped with pinkish or white patches. This combination of a pale, pointed face with dark, bead-like eyes is what most people remember from a nighttime encounter.
Less obvious but just as important are the whiskers. Opossums have well-developed facial whiskers, called vibrissae, which they use to navigate their environment in the dark. Research on the gray short-tailed opossum found that the whiskers are arranged in a grid-like pattern of rows and arcs, with about 23 whiskers on each side of the face organized in four rows. Each whisker follicle has a defined capsule and can contain specialized sensory structures, including cavernous and ring sinuses that help detect vibrations and contact.1Journal of Experimental Biology. The evolution of active vibrissal sensing in mammals: evidence from vibrissal musculature and function in the marsupial opossum Monodelphis domestica These whiskers are actively swept back and forth in a behavior called whisking, at a frequency of roughly 7 to 8 cycles per second in opossums, which helps the animal map out objects and terrain in near-total darkness.2PubMed Central. Active vibrissal sensing in rodents and marsupials
Fur, Coat Color, and Texture
The Virginia opossum’s outer fur is coarse and somewhat scraggly-looking. It consists of two layers: a dense, soft undercoat that is typically white or pale, and longer, coarser guard hairs that give the animal its overall color. Those guard hairs are usually gray or grayish-brown, though they can have a slightly silvery cast. The undercoat peeks through in spots, giving the animal a somewhat disheveled look. The face tends to be much paler than the body, and the legs are usually darker, sometimes nearly black.
Australian brushtail possums show a wider color range, from silver-gray to dark brown to fully black. Research into the genetics behind these color differences found that black coat color in brushtail possums is tied to a specific variant in the ASIP gene. Possums carrying two copies of a particular allele at this location have black fur, while those with one or two copies of the standard allele stay gray.3PubMed Central. Coat colour in marsupials: genetic variants at the ASIP locus determine grey and black fur of the brushtail possum A small number of brushtail possums from New Zealand were classified as “red,” and genetic testing showed these individuals carried the same genotype as black possums, suggesting reddish fur is controlled by a separate mechanism rather than being part of the same gray-to-black spectrum.3PubMed Central. Coat colour in marsupials: genetic variants at the ASIP locus determine grey and black fur of the brushtail possum
If you encounter a possum and it looks like a scruffy, patchy mess, that is actually normal. Opossums are not sleek animals. Their guard hairs grow unevenly, and it is common to see bare patches, especially on the ears and tail. The overall impression is something between a very large rat and a small, unkempt cat.
The Prehensile Tail
Perhaps no feature gets more attention than the opossum’s tail. It is long, usually about a third of the animal’s total length, and almost entirely hairless. The skin is scaly and pale, sometimes pink near the base and darker toward the tip. For many people this is the feature that triggers a “that’s a giant rat” reaction, but the tail’s function is much more sophisticated than anything a rat uses its tail for.
The Virginia opossum’s tail is prehensile, meaning it can grip and wrap around objects like a fifth limb. Opossums use it to stabilize themselves in trees, to carry nesting material, and to anchor themselves while reaching for food. This gripping ability comes from a specialized muscular architecture. Studies comparing the tail muscles of arboreal opossums (like the Central American woolly opossum) with ground-dwelling species found significant differences in the types of muscle fibers present. Arboreal species had a higher proportion of fast-twitch hybrid fibers, which support the sustained and powerful grip needed to hang from branches and maneuver through canopy.4PubMed Central. Myosin isoform expression in the prehensile tails of didelphid marsupials: functional differences between arboreal and terrestrial opossums
Despite the popular image, adult Virginia opossums do not actually hang from trees by their tails for extended periods. The tail can support their weight briefly, and young opossums sometimes dangle while playing, but the tail functions more as a counterbalance and stabilizer than a permanent hanging device. Australian possums also have prehensile tails, though the brushtail possum’s tail is furred along its upper surface and bare on the underside, a noticeable difference from the completely naked tail of the Virginia opossum.
Teeth and Mouth
Opossums have more teeth than any other North American land mammal. The Virginia opossum carries 50 teeth, which are visible when the animal opens its mouth in a defensive display. This open-mouth threat posture, with all those tiny sharp teeth on display and often accompanied by hissing and drooling, is one of the most commonly photographed opossum behaviors. The teeth are small and pointed, suited to an omnivorous diet that includes insects, fruit, carrion, small vertebrates, and just about anything else edible.
The dental arrangement is distinctive: opossums have a set of small incisors at the front, prominent canines, and a row of sharp premolars and molars behind them. The upper jaw has slightly more incisors than the lower. This dental formula is considered primitive among marsupials, meaning it closely resembles the ancestral condition for the whole group. Practically speaking, it means opossums can eat almost anything, which is a big part of why they thrive in such a wide range of habitats.
Feet and the Opposable Thumb
Look at an opossum’s hind feet, and you will notice something unusual: a large, clawless, thumb-like toe that sticks out at a wide angle from the other toes. This opposable hallux works like a human thumb, giving the opossum a powerful grip on branches. The front feet have five toes as well, each tipped with a small claw, and they are used for digging and grasping food. All the toes on both front and hind feet have fleshy pads, which help with grip on bark and smooth surfaces.
The skeletal structure supporting this locomotion reflects the opossum’s generalist lifestyle. Studies of the axial skeleton in South American opossums noted that various features of the vertebral column relate to how the animal moves: the shape and orientation of the spinal processes, the length and curvature of the lumbar vertebrae’s transverse processes, and the robustness of the tail vertebrae all differ depending on whether a species is primarily arboreal, terrestrial, or semi-aquatic.5PubMed Central. Functional-adaptive anatomy of the axial skeleton of some extant marsupials and the paleobiology of the paleocene marsupials Mayulestes ferox and Pucadelphys andinus The Virginia opossum is a decent climber but spends plenty of time on the ground, and its skeleton reflects that middle-ground approach.
The Pouch and Reproductive Anatomy
Female opossums have a pouch, or marsupium, on their abdomen. It is not as deep or well-formed as a kangaroo’s pouch, but it serves the same basic purpose: protecting and nursing the tiny, underdeveloped young that are born after a very short gestation period (about 12 to 13 days in the Virginia opossum). The babies, each roughly the size of a honeybee at birth, crawl into the pouch and attach to a teat.
The number of teats inside the pouch varies. In the common opossum (Didelphis marsupialis), adults typically have around five teats, though the range extends from zero to ten. Subadults in one study had the highest average teat count at eleven, which researchers interpreted as an adaptation to the reproductive demands these animals face.6PubMed Central. Reproductive tract and pouch anatomical variability across the reproductive phases in female common opossum (Didelphis marsupialis Linnaeus, 1758) Since opossums can give birth to a dozen or more young at once, having enough teats matters. Any babies that do not manage to latch on will not survive.
Male opossums have a feature that surprises many people: a bifurcated (forked) penis, which corresponds to the female’s paired reproductive tract. This is a marsupial trait, not unique to opossums, but it is one of those anatomical details that comes up when people look closely at these animals and wonder what they are seeing.
What “Playing Possum” Actually Looks Like
The phrase “playing possum” comes from the Virginia opossum’s dramatic involuntary response to extreme threat. When severely stressed, an opossum can enter a catatonic state that closely mimics death. The animal goes rigid, falls onto its side, and lies completely still with its mouth open and tongue lolling out. Research on this behavior found that the response is accompanied by drooling, urination, defecation, and in males, erection of the penis.7PubMed. Physiological responses associated with feigned death in the American opossum The animal shows no response to being touched or pinched during the episode. The eyes may be open or closed, and the body remains stiff.
This is not a conscious decision. It appears to be an involuntary physiological reaction, more like fainting under extreme stress than a deliberate act. The episode can last from a few minutes to several hours. During this time, the opossum’s heart rate and breathing slow dramatically. From a physical standpoint, a “playing possum” opossum looks genuinely dead: limp body, open mouth, no reaction to stimuli. The combination of the rigid body posture and the foul-smelling secretions makes the animal unappealing to many predators that prefer live prey.
Scent Glands and Chemical Signals
You will not see scent glands by looking at a possum, but they shape a lot of the animal’s social life. Australian brushtail possums have specialized scent glands that they use to mark territory and communicate with other possums. These glands are located in several places on the body, including the chest (a sternal gland that produces a reddish-brown secretion) and near the cloaca.8New Zealand Journal of Zoology. Scent glands of the common brushtail possum (Trichosurus vulpecula) The sternal gland is especially noticeable in mature males, where the fur on the chest can be stained brown from repeated marking. Virginia opossums also have scent-marking behavior, though their glandular anatomy is less well studied than that of their Australian relatives.
If you have ever caught a musky, unpleasant smell near an opossum, you are probably detecting these glandular secretions rather than poor hygiene. Opossums are actually quite clean animals that groom themselves regularly.
How Australian Possums Differ in Appearance
People outside Australia and New Zealand tend to lump all possums together, but the physical differences between North American opossums and Australian possums are dramatic. The common brushtail possum (Trichosurus vulpecula) has a round face, large pointed ears, a bushy (not naked) tail, and thick, soft fur that looks well-groomed compared to the scraggly Virginia opossum. Brushtail possums are about the same size as a large house cat, and their large, forward-facing eyes give them a much more conventionally appealing look. The ringtail possum is smaller still, with huge dark eyes, a thin curling tail, and a face that looks more like a small lemur than anything you would find in a North American backyard.
The differences run deep, not just in appearance but in ecology. Australian possums are mostly herbivorous, eating leaves, flowers, and fruit, while the Virginia opossum is a committed omnivore. This dietary difference shows up in their teeth and jaw shape: Australian possums have broader, flatter molars for grinding plant material, while opossums have the sharp, generalized teeth described earlier.
Sugar Gliders and the Gliding Membrane
One of the most physically striking members of the possum family is the sugar glider (Petaurus breviceps), a small Australian marsupial that can glide through the air using a thin membrane of skin stretched between its front and hind legs. This membrane, called the patagium, develops from the lateral skin between the limbs shortly after birth and extends outward over subsequent days.9Nature. Emx2 underlies the development and evolution of marsupial gliding membranes When a sugar glider launches itself from a tree, it spreads its limbs and the patagium unfurls like a kite, allowing the animal to glide distances of 50 meters or more.
The membrane is not just a flap of loose skin. It contains a complex of muscles that the glider uses to control its trajectory in the air. The most prominent of these are the humerodorsalis and tibioabdominalis muscles, along with a well-developed tibiocarpalis muscle on the outer edge of the membrane. Researchers believe this muscular system acts as a membrane controller during flight, allowing the glider to steer, adjust its glide angle, and brake before landing.10Annals of Anatomy – Anatomischer Anzeiger. Functional anatomy of gliding membrane muscles in the sugar glider (Petaurus breviceps) The genetic machinery behind the patagium’s development involves the expression of a signaling molecule called Wnt5a, which promotes the differentiation of the membrane tissue during early life.11PubMed Central. Convergent deployment of ancestral functions during the evolution of mammalian flight membranes
Sugar gliders are tiny, weighing only about 100 to 160 grams, with enormous dark eyes adapted for nocturnal vision and a distinctive dark stripe running from the nose to the back of the head. They look nothing like the Virginia opossum, yet they are fellow marsupials in the broader possum lineage. The fact that “possum” covers both a scruffy garbage-raider in your backyard and a tiny, membrane-winged glider in an Australian forest gives some sense of how physically diverse this group of animals actually is.
Skin Development and How Opossums Build Their Coat
Because marsupials are born at such an early developmental stage, much of the physical appearance of a possum develops outside the womb. Newborn opossums are essentially embryonic: pink, hairless, and translucent, with fused eyelids and barely formed limbs. Research tracking skin development in the gray short-tailed opossum showed that hair covering, sweat glands, and subcutaneous fat appear by about day 28 of life, marking the point at which the skin shifts from a gas-exchange organ (the tiny newborn essentially breathes partly through its skin) to a thermoregulatory one. Total skin thickness increases from about 58 micrometers at birth to 726 micrometers by day 35, when the fur is fully developed.12PubMed Central. Skin development in the gray short-tailed opossum (Monodelphis domestica)-From skin respiration to thermoregulation
This means that for the first few weeks of a possum’s life, it looks nothing like the furry, pointed-faced animal you might eventually see crossing your fence at night. The transformation from a pink, bean-sized newborn to a fully furred juvenile happens entirely inside the mother’s pouch or clinging to her back, which is why most people never see a possum at that stage. By the time young opossums are visible riding on their mother, they already have their characteristic gray fur, dark ears, and developing whiskers. The animal that eventually ventures out on its own looks like a miniature version of the adult, though its face may be slightly rounder and its fur a bit softer before it takes on the coarser adult texture.