Maximum-likelihood ancestral state reconstruction of facial colour pattern complexity across the New World primate species studied. Warmer colours indicate higher complexity in facial colour patterns (i.e. faces with higher number of areas, as illustrated in figure 2b, that are uniquely different from other facial areas based on hair and skin colour). Species shown in illustrations are (1) Cacajao calvus, (2) Callicebus hoffmansi, (3) Ateles belzebuth, (4) Alouatta caraya, (5) Aotus trivirgatus, (6) Cebus nigritus, (7) Saimiri boliviensis, (8) Leontopithecus rosalia, (9) Callithrix kuhli, (10) Saguinus martinsi and (11) Saguinus imperator. Illustrations by Stephen Nash.
(a) The face of a white-faced capuchin monkey (Cebus capucinus) illustrating the procedure used to characterize facial colour pattern complexity. (b) Faces were subdivided into 14 areas which were used to record traits describing the hair and skin colour, and hair length. (c) These areas were then grouped into regions that covaried across species (A, crown; B, forehead; C, eye mask; D, nose–mouth; E, face margin). Bilaterally symmetrical areas or regions are shown for only one side of the face.
Geographical trends in pigmentation and hair length across facial regions. Arrows indicate the direction towards which facial parts become darker (regions highlighted in black) or hair becomes longer (region highlighted in grey). The distribution of Neotropical primates (black outline), the Equator and major lowland tropical biomes (white outlines) are indicated in the map.