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(hallux) and having two, rather than three, permanent molars. Goeldi's monkey (Callimico goeldii) has claws but also three molars, and some authorities prefer to consider it with the cebids; but we consider it with the marmosets and tamarins because all display the common adaptation of climbing main trunks with the aid of claws.
All callitrichids are small arboreal primates ranging from Costa Rica to southern Brazil and Bolivia in nature. The smaller forms, like the pygmy marmoset (Cebuella), at about 120 g (4 oz), subsist mainly on insects and tree saps obtained from gouge holes; medium-size marmosets, at 300–400 g (11–14 oz), and the larger tamarins (Saguinus and Leontopithecus) and Goeldi's monkey, at 600–1,000 g (1.3–2.2 lb), are more omnivorous, but marmosets are also heavily dependent on exudate feeding (Rylands 1993). Marmosets are often distinguished from tamarins by their procumbent incisors; tamarins also have more robust and longer canine teeth.
Comprehensive descriptions of the natural history, behavior, and communication of callitrichids can be found in Rylands (1993) for marmosets and tamarins, Soini (1988) for pygmy marmosets, Stevenson and Rylands (1988) for marmosets, Snowdon and others (1988) for tamarins, Kleiman and others (1988) for lion tamarins, and Heltne and others (1981) for Goeldi's monkey. The reproductive biology and captive breeding of marmosets and tamarins are summarized in Hearn (1983).
The ideal captive environment is conducive to good physical health, provides for successful reproduction and the raising of offspring, and enables animals to acquire the behavioral skills that they would need in their natural environment (Snowdon and Savage 1989). The size and, perhaps more important, the furnishings of the captive environment affect the behavior of callitrichid monkeys (Box 1988; Caine and O'Boyle 1992; Chamove and Rohrhubert 1989; Molzen and French 1989). Most studies have dealt with the positive effects of well-constructed environments on behavior, but Schoenfeld (1989) described the impoverishing effects of a drastic reduction in environmental complexity on social behavior and infant care in a family group of common marmosets.
Large cages, containing branches and other substrates for climbing, have been used successfully in many long-term breeding colonies. They promote physical well-being and meet the behavioral needs of laboratory primates. Caging should permit callitrichids to assume normal body postures (e.g., sitting on a support with the tail hanging down without touching the cage floor) and to engage to some extent in normal locomotor behavior, such as climbing, running, and jumping.
Wild marmosets and tamarins only occasionally descend to the ground and in captivity prefer to be above caregiving personnel (Poole 1990). Therefore, it is