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.