Physical characteristics

New World opossums are small- to medium-sized mammals. The tail can be almost completely covered with hair or almost naked, depending on the species, and frequently is bi-colored with the distant half whitish and the base dark. When the tail is naked, it is covered with scales. Tail length is as long as or longer than the head and body in all genera except Monodelphis, in which it is about 50% of the head and body length. In most genera, the tail is at least partially prehensile. Ears are always medium to large, rounded and naked, except in the genera Lutreolina and Lestodelphys, in which ears are short. The snout is long and pointed, and eyes are large, sometimes bulging, and black or brown. The mouth is large and can open to a remarkably wide gape. Tooth and skull morphology is notably consistent, indicating the relatively low level of specialization in this group. The dental formula is I5/4 C1/1 PM3/3 M4/4 X 2 = 50. The thumbs are opposable in the hind feet, giving extremities their characteristic grasping ability, although the water opossum has webbed feet to aid in swimming action and its thumbs are only slightly opposable. Arms and legs vary with the genus. Some genera,

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