Opossum

Opossums represent the oldest surviving mammal family. Ancestors resembling modern opossums lived on earth at the same time as the dinosaurs. Scientists have located seventymillion- year-old opossum fossils. The Virginia opossums are found in the United States and Canada, while relatives representing seventy species of the Didelphidae family live in Central and South America.

Anatomy
The Virginia opossum is the largest species of the Didelphidae family. They are about the size of a domestic cat and measure from 0.3 to 0.8 meters (1 to 2 feet) in length, with a 22 to 50 centimeter (9 to 20 inch) long tail. Their weight varies from 2 to 5.5 kilograms (4 to 12 pounds). Other opossums are much smaller, averaging 7.5 centimeters (3 inches) in length with a 5 to 10 centimeter (2 to 4 inch) long tail. Opossumshave varying lengths and thicknesses of fur, in shades of white, gray, brown, and black. Some opossums have stripes. Opossum eyes are black, and their ears are usually hairless. Their faces have a mask or are white. They have a pink nose at the end of a long, pointed, whiskered snout which has fifty sharp teeth. Their four feet and tail are also pink and hairless. Each forefoot has five toes with claws. Opossums have an opposable, thumblike toe on their hind feet that can grasp objects and cling to branches. They are arboreal animals and agile climbers. Their prehensile tails are used for balance.

Life Cycle
Male opossums attain maturity at eight months, and females are sexually mature between six and nine months. Female opossums can produce two litters annually. As many as fifty-six offspring may be in a litter, but, because female opossums can only nurse twelve to fifteen newborns in their marsupium, most newborn opossums die. Born blind, each newborn opossum, which is almost embryonic and as small as a bean, crawls from the birth canal near their mother's tail and across her stomach to her pouch. They attach to nipples inside the pouch, where they nurse for two to three months. This nursing period provides them with immunities to diseases. The babies stay inside the pouch when the mother leaves the den to forage. As they grow and the pouch becomes full, the young opossums sometimes briefly leave the pouch, then return for nourishment. Fromthe age of three to five months, the babies ride on their mother's back. While traveling this way, the young opossums gain scavenging and survival skills.

Behavior
Opossums tend to be solitary, nomadic animals that can range over 30 to 96 acres (0.5 to 1.5 square miles) daily. They nest in hollow trees and other animals' burrows. Opossums are nocturnal, foraging at night. Because they are adaptable, opossums can live in a variety of habitats and are frequently found in urban areas which formerly were wooded. They adjust their scavenging and living habits to find food and shelter whether they are in a rural setting or in the middle of a city. Extremely cold weather is the primary environmental condition that deters opossums from otherwise suitable habitats. Opossums are hardy and immune to most diseases. They are the mammal most resistant to rabies. Opossums are omnivorous and eat a variety of insects, especially crickets, beetles, and cockroaches. They also consume snails, slugs, snakes, worms, birds, and rodents in addition to carrion and eggs. Berries, fruit, and vegetables appeal to opossums, particularly when overripe. Opossums have keen senses of smell, vision, and hearing to locate sustenance and clean up organic wastes in their territories. The life expectancy of opossums is one to three years in the wild and as many as ten years when kept in captivity. In addition to being preyed upon by wildlife and domesticated animals, opossums are killed by humans for sport, fur, and meat, or by accident with vehicles. Baby opossums often survive automobile impacts which kill their mothers. Opossums show a variety of defense mechanisms: They move more slowly than their predators and often spray a foul-smelling secretion to thwart attacks. Virginia opossums feign death by becoming limp when frightened and unable to escape. They sometimes hiss or growl, exposing their teeth. Opossums occasionally fight and bite. Opossums hide in brush-covered areas that are difficult for predators to access. They can make sounds, including screeches, but are usually quiet. Scientists have gauged opossums' ability to learn and distinguish objects as greater than that of dogs and almost equivalent to pigs.