You can spell Possum both "opossum" or "possum". Both mean small Australian arboreal marsupial having long prehensile tails.
Mammals of Australia
The mammals of Australia have a rich fossil history, as well as a variety of extant mammalian species, dominated by the marsupials, but also including monotremes and placentals. The marsupials evolved to fill specific ecological niches, and in many cases they are physically similar to the placental mammals in Eurasia and North America that occupy similar niches, a phenomenon known as convergent evolution. For example, the top predator in Australia, the Tasmanian Tiger, bore a striking resemblance to canids such as the Gray Wolf; gliding possums and flying squirrels have similar adaptations enabling their arboreal lifestyle; and the Numbat and anteaters are both digging insectivores.
The fossil record shows that monotremes have been present in Australia since the Early Cretaceous 145–99 MYA.
A prehensile tail is the tail of an animal that has adapted to be able to grasp or hold objects. Fully prehensile tails can be used to hold and manipulate objects, and in particular to aid arboreal creatures in finding and eating food in the trees. If the tail cannot be used for this it is considered only partially prehensile - such tails are often used to anchor an animal's body to dangle from a branch, or as an aid for climbing. The term prehensile means "able to grasp" (from the Latin prehendere, to take hold of, to grasp).
One point of interest is the distribution of animals with prehensile tails. The prehensile tail is predominantly a New World adaptation, especially among mammals. Many more animals in South America have prehensile tails than in Africa and Southeast Asia. It has been argued that animals with prehensile tails are more common in South America because the forest there is denser than in Africa or Southeast Asia. In contrast, in less dense forest such as in Southeast Asia it is observed that gliding animals such as colugos or flying snakes are more abundant; few gliding vertebrates are found in South America. South American rainforests also differ by having more lianas, as there are fewer large animals to eat them than in Africa and Asia; the presence of lianas may aid climbers but obstruct gliders. Curiously, Australia-New Guinea contains many mammals with prehensile tails and also many mammals which can glide; in fact, all Australian mammalian gliders have tails that are prehensile to an extent.
Common ringtail possum
The Virginia opossum (Didelphis virginiana), commonly known as the North American opossum, is the only marsupial found in North America north of Mexico. In the United States it is typically referred to simply as a possum. A solitary and nocturnal animal about the size of a domestic cat, and thus the largest opossum, it is a successful opportunist. It is familiar to many North Americans as it is often seen near towns, rummaging through garbage cans, or lying by the road, a victim of traffic.
In Mexico it is known as the tlacuache.
The common ringtail possum (Pseudocheirus peregrinus, Greek for "false hand" and Latin for "pilgrim" or "alien") is an Australian marsupial. It lives in a variety of habitats and eats a variety of leaves of both native and introduced plants, as well as flowers and fruits. The Ringtail Possum does not occur in New Zealand. This possum also consumes a special type of faeces that is produced during the daytime when it is resting in a nest. This behaviour is called coprophagia and is similar to that seen in rabbits.