A rather sophisticated 'mutual-aid' style
variation on the monogamous family unit is found in the tamarins
and marmosets: all members of the family, from father to mature
offspring, take part in the care of the newborn young.
Another interesting slant to the lives of the callitrichids is
their heavy reliance on scent marking to define territory, a custom
which is rare or absent in most Old and New World monkeys but
common among the Madagascan lemurs. Saddle-back tamarins apply
scent marks to lianas and slim branches using three different
methods: ano-genital, by sitting upright and rubbing their
backsides against the branch with a rotating action, possibly at
the same time reinforcing the message with a spattering of urine;
suprapubic marking, in which the animal lies prone and pulls itself
forwards with its arms, massaging the suprapubic region against the
bark to smear it with scent; and, much more rarely, sternal
marking, in which the chest is rocked to and fro against the bark.
As in lemurs, most of this activity is concentrated around the
periphery of the home range. Scent marking may be applied more
intensively on a number of favourite spots, such as a certain liana
which may attract a thorough going over from the whole group in
concert.