The animal commonly known as the possum in North America, properly called the Virginia Opossum, is definitively a marsupial. This classification places it within the infraclass Marsupialia, a group of mammals characterized by a unique reproductive strategy. The opossum is the only marsupial species found north of Mexico, making it a distinct biological anomaly in the region.
What Makes an Animal a Marsupial
Marsupials are distinguished from placental mammals by a difference in their reproductive process. They undergo an extremely short gestation period, meaning the young are born at a highly underdeveloped, almost embryonic stage. Unlike placental mammals, where the embryo develops extensively inside the mother’s uterus, marsupial development largely occurs externally.
The newly born, immature young must crawl immediately after birth to a specialized pouch, or marsupium, on the mother’s abdomen. Once inside the pouch, the young latch onto a nipple to complete their growth and development. The existence of this specialized post-birth development is the defining characteristic of all marsupials.
The Life Cycle of the American Opossum
The North American Opossum (Didelphis virginiana) exemplifies the marsupial reproductive strategy. The entire pregnancy lasts a mere 11 to 13 days, exceptionally brief for a mammal of its size. At birth, the newborns are tiny, altricial, and larval-like, weighing only about 0.13 grams.
These minuscule young must immediately begin climbing across the mother’s fur toward the pouch entrance. They use their relatively developed forelimbs to navigate this journey to the marsupium. The female typically has 13 teats inside her pouch, and only the young who successfully attach to a nipple will survive.
Once attached, the young opossum remains locked onto the nipple for approximately 50 to 65 days, ensuring continuous nutrition and rapid growth. They stay within the pouch for a total of about 2.5 months before they are developed enough to venture out. After leaving the pouch, they often spend additional time clinging to their mother’s back, a behavior known as “caravaning,” before becoming fully independent.
Clearing Up the Possum vs. Opossum Confusion
A source of public confusion stems from the common use of the shortened name “possum” for the North American animal. While widely accepted as a nickname, the full and correct name for the animal found throughout the Americas is “opossum.” The original name comes from the Algonquian language, meaning “white dog or beast.”
The term “possum” technically refers to a different, though related, group of marsupials found exclusively in Australia and its surrounding islands. Australian possums, such as the Brushtail and Ringtail species, are part of the marsupial order Diprotodontia, which also includes kangaroos and wombats.
The American opossum belongs to a separate order, Didelphimorphia, meaning the two groups evolved along distinct evolutionary paths. Despite the similar names and shared marsupial classification, the American Opossum and the Australian Possum are not closely related, a distinction comparable to that between an elephant and a manatee. The name “possum” was simply applied to the Australian animals by early European settlers who thought they resembled the American opossum they had already encountered.