which allow the condyles to attach. Anterior margin of the lacrimal fossa is formed by or near the maxilla. The premaxilla is short, giving the appearance of a small, not especially prognathic face relative to other platyrrhines. The corpus of the mandible deepens posteriorly and the ramus is tall. The hyoid bone is expanded and highly convex ventrally. Behavior and ecology Groups vary in size from two to four individuals usually with an adult female and an adult male. The young tend to leave group at the age of 2–3 years old. It rarely interacts with other primates. Bonding between male and female pairs is extremely strong. Once this relationship is established, partners remain very close to each other. Couples also intertwine the tails whenever possible. Couples tend to follow each other and remain near each other throughout the day. The males play a major role in taking care of the young. Siblings however, do not play a role and do not usually help in rearing of the young. The adults use chest rubbing as a visual signal, dragging branches along their chest slowly. Later, after brushing, the area is smelt or rubbed. It tends to inhabit lower and denser tropical forest especially close to rivers and river banks. It has a frugivorous diet, eating anything from fruits and twigs to leaves and insects. It has a relatively small home range. Like other titis, it is highly territorial and sends out vocal calls to mark territory and scare off other animals. Grooming occurs frequently throughout the day, mostly during rest periods. Both females and males, adults and young participate in grooming. It has been suggested that grooming is a form of habituation introducing the concept of presence and physical contact with companions. Adults and juvenile also intertwine tails with the opposite sex whenever two from the same social group are by each other. The red-bellied titi has a variety of postures and facial expressions that it uses as visual signals. Swaying the entire body, turning the head sideways and lowering the head to face downward are examples of these signals. Observers have seen that these signals are a response to a disturbance or escape tendencies. Arching of the back is a signal that the red-bellied titi uses to warn that they're about to attack. This signal is associated with hostility, after they arch their backs an attack usually follows. Other