Didelids

Didelids are a group of marsupials belonging to the infraorder Didelphimorphia. This diverse group includes all the opossums and their close relatives, native to the Americas. They are characterized by their generally pointed snouts, often prehensile tails, and numerous small teeth. The number of teeth can vary, but many didelids possess fifty teeth, the most of any living mammal. This dentition is often considered primitive. Didelids exhibit a wide range of sizes, from the tiny mouse opossum to the larger Virginia opossum. Their habitats are equally varied, found in forests, grasslands, and even urban areas. Many didelids are nocturnal and omnivorous, feeding on insects, small vertebrates, fruits, and carrion. Reproduction in didelids is notable for the very underdeveloped state of the young at birth. They are born after a short gestation period and immediately crawl into the mother's pouch, where they attach to teats and complete their development. The Virginia opossum, Didelphis virginiana, is the only marsupial found north of Mexico. Other prominent didelids include the yapok or water opossum, the only aquatic marsupial, and various species of mouse opossums and shrew opossums. Their evolutionary history is ancient, with fossil evidence suggesting their lineage dates back to the Cretaceous period.