The common marmoset gives birth to twins.
ano-genital sniffing: This is where a male common marmoset sniffs the ano-genital region of the female in order to determine if she is in estrus (heat) and ready for copulation (Stevenson and Poole, 1976).
soliciting behavior: This is when the female stares at the male combined with a higher degree of rhythmic tongue protrusion and lip-smacking (Stevenson and Poole, 1976). This behavior pattern is more common in newly-mated pairs (Stevenson and Poole, 1976). The males respond to this behavior by approaching the female and performing rhythmic tongue protrusion and lip-smacking (Stevenson and Poole, 1976).
Before copulation ano-genital sniffing, neck nuzzling (a specialized form of face nuzzle), and handling of the female by the male take place by the male (Stevenson and Poole, 1976). Copulation is defined by Stevenson and Poole (1976) as "the period extending from the first mounting of the female by the male, followed by pelvic thrusting until the male dismounts."
[Primate Fact Sheets]