Look at the common marmoset family. Do you see any young marmosets in the enclosure righ now? If yes and you happen to see young marmouset riding on someones back, then most likely that adult is male. Baby marmousets are under his father (and ohter male relatives) protection and most of the time young animal is riding on his father’s back. Males taking care of the offspring is not so common behavior in the nature. What do you think, why it might be important for this species females to share the burden of growing the babies with males?