IV. SOME GENERAL CONSIDERATIONS ON THE SYSTEMATICS AND TAXONOMY OF NEOTROPICAL PRIMATES

All neotropical primates belong to the infraorder Platyrrhini of the suborder Anthropoidea. With the exception of Uruguay and Chile, platyrrhines are widely distributed throughout the tropical forests of Central and South America, from the south of Mexico to the extreme south of Brazil and the northern parts of Argentina and Paraguay, and on some Caribbean islands.

Habitats of New World primates are sometimes inaccessible, thus limiting the possibilities to study their ecology, behaviour, and population dynamics, as well as their systematic position.

Primate taxonomists are confronted with serious problems in obtaining specimens and biological samples for description and definition of species. Due to their beauty, elegance, and human-like appearance primates were and still are captured and sold as pets and for zoological gardens, thereby changing ownership several times. The same may have happened to collections and single specimens for museums which were transferred far away from their place of origin. Events like these have led to confusion with regard to the geographic origin of specimens and have resulted in errors that still survive in the literature. Intraspecific phenotypical variation and sexual dimorphism in the genera Pithecia and Alouatta modify the external appearance of animals and can lead to complications in the taxonomic diagnosis. Progress in genetics as well as in ecology and behavioral biology have reenforced the value of traditional diagnostic characters for actual taxonomic revisions.

Platyrrhines are characterized externally by the presence of a flattened nose, with the nasal openings generally pointing laterally and separated by a broad cartilage, and by the absence of ischial callosities. The pelage may include structures that appear like a mantle as in Saguinus nigricollis, like a hood, as in Cebus monkeys, like a hair tuft, as in Ateles, or like a beard, as in Alouatta. The face may be naked as in Cacajao, Alouatta, Ateles y Lagothrix or it may bear a long moustache as in Saguinus imperator.

The tail is generally long, except in Cacajao, where it is short and very bushy, and in Pithecia, where it is moderately long with plume-like, coarse hair. In Ateles, the length of the tail is nearly twice the body length. The ventral side of the terminal portion of the prehensile tail of Alouatta, Ateles and Lagothrix is naked and covered with dermatoglyphs, while the semi-Prehensil tail of Cebus is completely covered with hair and lacks the dermatoglyphs.

With regard to size and body weight, three groups can be distinguished within the platyrrhines. Large species (Alouatta, Ateles, and Lagothrix) with a length up to 150 cm (head + body + tail) and a weight up to 10 kg; medium-sized species (Cacajao, Pithecia and Cebus) with a length up to I 10 cm and a weight up to 4 kg; and small species with a length up to 85 cm and a weight up to I kg (Aotus, Callicebus, Saimiri and the Callitrichidae), including the tiny Cebuella with 35 cm length and up to 150 g of weight.

All New World monkeys are arboreal, but some species like Callimico goeldii and Saguinus fuscicollis occasionally forage in the leaf litter, and others like Cebus, Ateles and Lagothrix may walk bipedally on the ground for short distances. With the exception of Aotus, all species are diurnal. Squirrel monkeys (Saimiri) may be crepuscular and howler monkeys (Alouatta) generally emit their loud calls and roars at dawn.
The majority of primates in Peru are basically frugivores, but their diet may also include substantial amounts of leaves, insects and other invertebrates, gums, nectar, eggs, and small to medium-sized vertebrates.

For the 32 primate species known from Peru and described in this book, we have adopted the classifications of HILL (1960), NAPIER & NAPIER (1967), and HERSHKOVITZ (1977). The latter author recognizes three families of the infraorder Platyrrhini: the Callitrichidae (marmosets and tamarins), the Callimiconidae (Goeldi's monkey), and the Cebidae (capuchin-like monkeys).

The Callitrichidae include the smallest New World primates. Their digits except the large toe, bear claw-like nails, the forehead is strongly receding, and their 32 permanent teeth are arranged according to the dental formula:

The monotypical family Callimiconidae represents a "transition" between the other two families. The external morphology is similar to callitrichids, especially the presence of claws on all digits except the large toe, but aspects of the internal morphology and the number of molars correspond to the Cebidae.

The Cebidae have a rounded braincase and their 36 permanent teeth are arranged according to the dental formula:

This family is subdivided into the subfamilies Saimiriinae, Aotinae, Callicebinae, Pitheciinae, Cebinae, Alouattinae and Atelinae (Appendix II).