This species could be considered an intermediate form between the tamarins and marmosets and the cebids. The Goeldi's marmoset has claws instead of nails, except for the hallux, which has a nail (Heltne et al., 1981), like the marmosets, and three molar teeth, which is like the cebids. Also like the cebids the molars are quadritubercular (Heltne et al., 1981). This species has a dental formula of 2:1:3:3 on both the upper and lower jaws (Heltne et al., 1981). The scapula is unique in shape having the superior scapular border and the spinous process parallel in length, and this may assist in quadrupedal locomotion (Davis, 1994). The pelage color for this species is black, and the pelage ranges from 1 to 2 centimeters long over the body (Heltne et al., 1981). The skin of lips, snout, rims of ears, and the dorsal and volar surfaces of the hands and feet are colored black, with the skin of face being slightly lighter in color (Heltne et al., 1981). The remaining skin is colored bone-white or pink, but is usually covered by thick pelage (Heltne et al., 1981). Around the ears and going down the cheeks to the lips are hairs longer than found on the face (Heltne et al., 1981). The infant pelage may vary from the adult's in that the saddle hairs may have a whitish or golden terminal band (Heltne et al., 1981). Also on the ventral surface of the infant there is a glandular area over the manubrium containing hairs that are slightly longer than the other hairs found on the ventral surface (Heltne et al., 1981). The mean body mass for adult males was found to be 366 grams and for females it is 355 grams (Encarnacion and Heymann, 1998).
The Goeldi's marmoset is found in the upper Amazonian rainforests of Southern Colombia, Eastern Ecuador, Eastern Peru, Western Brazil, and Northern Bolivia (Nowak, 1999). This species is found from the south bank of the Caqueta River in Colombia, through the Amazonian region of Peru and Ecuador to the north of the Madre de Dios River in western Pando Bolivia (Heltne et al., 1981). This species has also been found to occur in South-western Brazilian Amazonia in the state of Rondonia, north of the Abuna River (Ferrari et al., 1999). This species prefers bamboo, mixed secondary, and scrub forests (Heltne et al., 1981). In the Andean foothills, this species occurs at a level up to 500 meters (Heltne et al., 1981). In Bolivia this species was always found in primary riverine forests, usually at heights ranging from 0 to 9 meters (Christen and Geissmann, 1994; Christen, 1999). In the dense lower levels of bamboo forests, this species prefers to live 1 to 3 meters above the ground (Davis, 1994).
The diet of Goeldi's marmoset includes fruit, berries, insects, and spiders (Heltne et al., 1981). This species has been found to consume the fruit of Cecropia morassi (Heltne et al., 1981). This species was also found to consume fruit from the species Pseudolmedia macrophylla trecul and Pourouma cecropiaefolia (Buchanan-Smith, 1991). This species will forage at the tops of trees for fruit from the species Piptadenia sp. and Clarisia racemosa (Pook and Pook, 1981). Generally this species feeds at the lower levels of the forest and at the ground, but occasionally will forage for fruit in taller trees (Heltne et al., 1981). This species has been observed to eat cacao from plantations. Goeldi's marmoset will jump to the ground to capture insects (Heltne et al., 1981). Insects found to be consumed include moths and grasshoppers, and live animals tend to be eaten head first (Heltne et al., 1981). In the late dry season this species relies heavily on fruit from the genera Piptadenia and Cecropia (Pook and Pook, 1981). During the wet season groups will range further than the dry season in search of ripening fruit (Pook and Pook, 1981). This species obtains its water from pools found on the ground as opposed to licking it from leaves as is more commonly found in the callitrichids (Heltne et al., 1981).
This is a diurnal and an arboreal species. Group sizes for this species range from 5 to 8 individuals (Heltne et al., 1981). In Bolivia it was found that group sizes for this species ranged from 2 to 5 individuals (Christen and Geissmann, 1994). The group begins traveling during the day around mid-morning, and alternates between traveling, feeding, and resting for the rest of the day (Heltne et al., 1981). When traveling, groups tend to use certain routes and tend to use the outer parts of the home range (Pook and Pook, 1981). When resting, social grooming is an activity that frequently occurs (Heltne et al., 1981). This species will rest in subgroups of 1-4 individuals separated by several meters (Pook and Pook, 1981). Groups of Goeldi's marmosets tend to be isolated from each other separated by several kilometers (Pook and Pook, 1981). This species will sleep in trees 10 to 15 meters in height (Heltne et al., 1981). This species has found to sleep in groups in holes in trees (Masataka, 1981b). Groups have also found to sleep in dense thickets of vegetation (Pook and Pook, 1981).
This species moves quadrupedally through the forest. The basic gait is a gallop, from which a leap or a pounce may come from, especially when moving quickly towards a highly desirable food source (Heltne et al., 1981). This species also moves from vertical to vertical trunk by leaping, and this species prefers to move at the lower levels of the forest (Heltne et al., 1981). When leaping, this species will use its hindlimbs to generate momentum (Heltne et al., 1981). This species will leap from one cluster of thin branches to another over a distance of 6-8 meters (Christen, 1999). Goeldi's marmoset will descend trunks either head first like members of the genus Saguinus or backwards like the cebids do (Christen, 1999).
The Goeldi's marmoset lives in groups of sizes from two to ten individuals. There is communal care of the offspring, usually by older offspring who have not left the group. This species has been shown in captivity to have a monogamous breeding system, although in the wild it may be polygynous (Carroll, 1988). Encarnacion and Heymann (1998) found that this species in the wild is polygynous. These older offspring are suppressed reproductively. Lyon et al. (1985) found that a two year old female was peripheralized in a group following a birth in the group. Carroll (1993a, 1993b) found that there is not any evidence for a lasting pair bond between males and females. Though not much agonism has been observed between males and females in pairs (Carroll, 1985). Contact and proximity within a pair is initiated and maintained at a higher frequency by the male more than by the female (Carroll, 1985). Males tend to guard their mates from predators and other conspecific groups (Carroll, 1985).
Goeldi's marmoset forms mixed-species associations with Saguinus fuscicollis and Saguinus labiatus (Pook and Pook, 1982; Christen and Geissmann, 1994; Buchanan-Smith, 1991). This species has also been found to form mixed-species associations with Callicebus moloch (Pook and Pook, 1982). There is a greater preference for this species to be associated with Saguinus fuscicollis rather than Saguinus labiatus (Pook and Pook, 1982). In Bolivia mixed groups of Goeldi's marmoset, Saguinus labiatus, and Saguinus fuscicollis would spend most of the day together, except for splitting during midday, then in late afternoon splitting up again to go to separate sleeping sites (Pook and Pook, 1982; Christen and Geissmann, 1994). These mixed groups would most often visit feeding trees during the early morning and mid-afternoon, and in late morning forage more for insects (Pook and Pook, 1982). These mixed groups maintained contact and spacing by the use of shrill calls (Pook and Pook, 1982). These shrill calls were most often heard early in the morning then decreased in frequency when the group comes together (Pook and Pook, 1982). Christen and Geissmann (1994) also studying mixed-species associations in Bolivia, noted that the three different species used soft contact and long calls upon emerging from sleeping sites. When moving, Goeldi's marmoset tends to always be the species in the rear of the mixed-species group (Pook and Pook, 1982). There is no direct competition between members of the mixed-species group because each species uses a different level of the forest for foraging and traveling (Pook and Pook, 1982).
Infants for the first two weeks are exclusively cared for by the female. The female will transfer infants to the fathers about 3 weeks after birth and the father becomes an important caregiver for the infant, the infant returning mostly just to feed from the mother (Jurke and Pryce, 1994). Mothers become aggressive to infants between the ages of 2 to 5 weeks, helping to facilitate the transfer to the fathers (Jurke and Pryce, 1994). Female offspring tend to be transferred to their fathers earlier than male offspring (18 days versus 25.4 days) (Jurke and Pryce, 1994). Also male offspring were nursed longer as opposed to female offspring (2.4 times per hour versus 1.6 times per hour) (Jurke and Pryce, 1994). Paternal behavior may occur in Goeldi's marmoset because the demands of pregnancy and lactation are energy consuming for the female (Jurke and Pryce, 1994). Grooming of the infant has its highest occurrence in the fourth week, with the female performing a majority of the grooming (Masataka, 1981a). Infants will become more independent as non-mothers reject them (Masataka, 1981a).
Play tends to be an important behavior in infants and young, but this behavior is very rarely present in the behavioral repertoire of the adult (Heltne et al., 1981). In the young this behavior serves an exploratory and learning function (Heltne et al., 1981).
For Goeldi's marmoset the main predator is the Tayra, Eira barbara, which is a terrestrial carnivore (Christen and Geissmann, 1994). Another potential predator could be the jaguarundi, Herpailurus yaguarondi (Christen and Geissmann, 1994). This species was found to run down to the ground when a large buzzard would fly overhead (Pook and Pook, 1981).
This species gives birth to a single offspring, which differs amongst other callitrichids, twice a year (Fleagle, 1988). Twins have been noted to be born in captivity (Altmann et al., 1988). During the estrus period, the female is receptive for a mean length of seven days (Heltne et al., 1981). Gestation length for this species is 145-152 days (Carroll, 1993b).
The female will solicit copulations from the male by first stretching before the male then lifting the tail as she rises, exposing the genitoanal region and the base of the tail (Heltne et al., 1981). The female will pass repeatedly before the male, passing a dampened tail before the nose of the male (Heltne et al., 1981). Then the female will drop her head in front of the male facing him (Heltne et al., 1981). The male will then start grooming the female's crown then move to the back, followed by sniffing, nose rubbing, or licking the arch of the back (Heltne et al., 1981). The male then moves to a posterior position, behind the rump of the female, with the female raising her rump up towards the male (Heltne et al., 1981). If the female allows intromission, she will flatten her back, positioning the vulva for more easy access for the male (Heltne et al., 1981). During this time the female may lick towards the male or reach back and grab the arm or shoulder of the male and gentle pull at them (Heltne et al., 1981). Intromission is followed by a small number of thrusts, and ejaculation occurs during thrusting with the thighs and pelvis of the male quivering (Heltne et al., 1981). The male, during these thrusting bouts, may nose rube or lick the back of the female or scent lick the air (Heltne et al., 1981). After ejaculation, the male and female will lick and examine their respective genitals (Heltne et al., 1981).