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(Leontideus rosalia), also lion-headed marmoset, a platyrrhine monkey of the family Hapalidae. The length of the body is 30–35 cm; the tail is almost as long as the body. The silky fur is reddish gold, and the skin of the face, hands, and feet is black or dark red. The golden marmoset has a mane of long hairs that cover the ears. The hands and feet are elongate, and the thumbs very short. The number of young is usually two. Golden marmosets inhabit mountainous forests of southeastern Brazil. They feed on fruits, insects, eggs, small birds, and lizards. Their numbers are small. The golden marmoset is a protected species.