A MONKEY zoo is celebrating the birth of twin black-tailed marmosets.Shaldon Zoo was delighted when the rare South American monkeys were born earlier this month.Julie Matthews, education officer for the Trust, said: "We are particularly pleased with this birth as we coordinate this species within Europe, helping to manage this species as a self-sustaining population. "There are very few black-tailed marmosets within collections so it is an important birth for the programme."This is the third offspring, but first set of twins for mum, Melanie and Dad, Cal. The pair came to Shaldon from Exmoor Zoo in 2010. As is usual in these small South American monkeys the male undertakes the majority of the care of the babies, passing them back to the female for feeding.Marmosets from South America have large incisor teeth which they use to gouge holes in tree bark to get the sap. They have claws instead of nails (except the big toe) and use these to grip the trees as they climb and move about the forest. Their diet consists of fruit, flowers, insects and gum.Marmosets and tamarins belong to the family Callitrichidae which contains the smallest monkeys in the world. The name Callitrichidae means 'beautiful hair'.