Wied's marmoset has non-opposable thumbs and nails of the digits, which are more claw-like. The crown of this species black along with the ear-tufts (Stevenson and Rylands, 1988). Around the cheeks and the brow there is an area of gray-white coloration (Stevenson and Rylands, 1988). The body pelage is annulated black-gray-orange, with an annulated black-gray tail (Stevenson and Rylands, 1988). Wied's marmoset has a median nasal white stripe (Groves, 2001). The young have juvenile pelage that starts to change into adult pelage around 5 months of age (Stevenson and Rylands, 1988). Infants will start growing ear-tufts at two weeks (Stevenson and Rylands, 1988). The dental formula for this species is 2:1:3:2 on both the lower and upper jaws (Ankel-Simons, 2000).
Wied's marmoset is endemic to the Atlantic coastal forest of Brazil (Rylands et al., 1993). Wied's marmoset ranges between the Rio Jequitinhonha to the north and the Rio de Contas to the south in the state of Bahia (Mittermeier et al., 1982; Rylands et al., 1988). This species was found to live in evergreen hygrophylic forest, young and old secondary forests, in abandoned rubber plantations, restinga forest, and piacava forest (Stevenson and Rylands, 1988; Rylands et al., 1988; Rowe, 1996).
Wied's marmoset is a frugivore-insectivore, which also consumes flowers, exudates, nectar, lizards, snails, and frogs (Stevenson and Rylands, 1988; Rylands, 1989; Raboy et al., 2006). Plant galls have also been observed to be eaten by this species (Rylands, 1982, 1989). Grasshoppers were found to be the most preferred insect prey; these include the short-horned (Acrididae) and the long-horned (Tetigoniidae) types (Rylands, 1982). Insects disturbed by army ant, Eciton burchelli, raids are exploited (Rylands, 1982). This species has also been observed to eat stick insects, Phibalosoma phyllinum, (Rylands, 1982). Wied's marmoset also feeds on small lizards and frogs, eating the head first (Rylands, 1982). Snails are eaten by first biting off the apex of the shell and then removing the snail (Rylands, 1982). Small fruit is consumed by removing the fruit with either hands or mouth and eaten while being held in the hand, with the seeds and skin sometimes being discarded (Stevenson and Rylands, 1988). Large fruits are eaten from the branch (Stevenson and Rylands, 1988).
The basic family group is composed of the adult pair, their offspring, and sometimes other individuals (Alonso et al., 2000). Within the group, there are two subgroups, the adult pair and the juveniles (Alonso et al., 2000). New groups may form by splitting and dividing the home range (Rylands, 1982). This species has a polyandrous mating system. Adults spend little time in contact with juveniles (Alonso et al., 2000). Alonso et al. (2000) found that the strongest social bond is between juvenile group members, with the second most strongest between the adult pair. The hierarchy within the groups are maintained by agonistic vocalizations directed at a challenger (Alonso et al., 2000). Schaffner and Angel (1996) found that there is a clear hierarchy between related adult males in a group in terms of access to food, higher rates of sexual activity, and exhibiting higher rates of territorial behavior. One male will maintain proximity and have copulatory bouts with breeding females more than other group males (Schaffner and French, 1994). During female maximum fertility, one male will monopolize access to the female (Schaffner and French, 1994). Although recently, Schaffner and French (2004) have found that all group males will engage in sexual activity. This may be the result of sperm competition, weak social bonds between males and females, and the need for multi-individual infant care (Schaffner and French, 2004). In a captive experiment, French et al. (1993) found that males direct higher rates of agonistic threats towards unfamiliar intruders as compared to familiar intruders. Also when exposed to unfamiliar intruders, females will engage in territorial behavior while the males perform mate-guarding behavioral patterns (Schaffner and French, 1995).