INTRODUCTION Linnaeus chose the name Primates (“first ones”), and he had the courage to include humans. There are close to two hundred living species in the Order Primates. Representatives of this group can be found in most zoo collections. In fact, the statement could be made that every zoo has primates either in an exhibit, taking care of an exhibit, or visiting an exhibit. There are three major types of non-human primates: prosimians, monkeys, and apes. An additional way primates are identified is by their nose type and geographical location, shown here by the two sub-orders: 1. Strepsirhini (primates with nose leather, “wet-nosed”) All species in this sub-order have a moist nose that is fused with the upper lip, which results in a face with a limited range of expression. All strepsirrhines are prosimians. Lemuriformes (Madagascar prosimians – Old World): mouse lemurs, true lemurs, pro-lemurs, indris, aye aye, sifakas, and indris Lorisiformes (non-Madagascar prosimians – Old World): Lorises, pottos, galagos 2. Haplorhini (primates without nose leather, “dry-nosed”) Tarsiiformes (dry-nosed prosimian – Old World) tarsiers Platyrrhini (broad-nosed monkeys – New World) o Cebidae: owl monkey, squirrel monkey, titis, sakis, howlers, spider monkey, and capuchins o Callithricidae: marmosets and tamarins o Callimiconidae: callimicos Catarrhini (narrow nosed monkeys and apes – Old World) o Cercopithecoidea (tailed Old World monkeys) • Cercopithecine: macaques, baboons, mangabeys, guenons • Colobine: langurs, colobus, proboscis, guerezas o Hominoidea (human-like apes) gibbons, orangutans, gorilla, chimpanzee, human Characteristics Specific to the Type of Primates PROSIMIANS Prosimians means "before monkeys" and show many, but not all, of the characteristics of monkeys. Like monkeys, they have flat nails and fleshy pads on most digits. First fingers and toes are opposable. However, unlike monkeys, they have a claw (used for grooming) on the second toe, and their skulls have many characteristics like insectivores, such as pointed snouts. They have a more developed sense of smell than monkeys. A keen sense of smell is helpful to nocturnal terrestrial animals like prosimians, while a more developed sense of vision is helpful to arboreal, diurnal animals like monkeys. They have prominent whiskers. Generally, they have definite breeding season. Their eyes, which are used for orientation and searching for food, are noticeably large (adapted for nocturnal vision); their sense of hearing is well developed. The tail is generally long and bushy. Most have a dental grooming comb. In behavior, there is a good deal of diversity. Most are good climbers and leapers. Females are dominant in all lemur species and have their own hierarchy within the group. There are six families of prosimians, and all are Old World primates. Prosimians are considered less complex than monkeys and apes and have characteristics that are primitive in comparison: • Reduced brain size • Olfactory lobes of the brain are larger than that in Haplorrhines, which shows a greater reliance on smell as a sense. • They have a rightly cluster incisors and canines in the mandible, which form the “dental comb” used in grooming. • Feet of prosimians have two distinct anatomical specializations (see photo): i. The big toe is widely separated from other toes, allowing for a secure grip during locomotion. ii. The second toe has a distinctive grooming claw. The other toes have nails. The exception is the aye-aye, which has claws on toes 2 through 5. • Most prosimians have relatively large eyes, and on the back of the retina majorities have a high reflective layer called the tapetum. The tapetum acts to intensify light that comes into the eye at night. This is more common in the nocturnal prosimians, which make up about seventy five percent of Strepsirrhines. • Reproduction with prosimians is unique compared with Haplorrhines. i. All prosimians have a breeding season rather than individual cycles. ii. Many have litters of offspring as well as multiple nipples (ruffed lemurs). MONKEYS Like prosimians, but unlike apes, monkeys have tails. They have flat nails on their digits, although in the marmosets and tamarins, the nails are claw-like. Opposition of thumbs and big toes is of varied degrees, but generally they are better graspers than prosimians and not quite as good as apes. Their limbs are of roughly equal length. Their shoulders do not rotate which means they are leapers, runners and climbers rather than brachiators. They have a more developed sense of vision than prosimians. Monkeys do not have the dental grooming comb of the prosimians. Their eyes face forward and are adapted to diurnal vision, their heads are rounded, and most have a short muzzle, as opposed to the prosimians. They do not have whiskers. Old world monkeys and lesser apes have ischial callosities, which are specialized tissue pads on their rumps otherwise known as “sitting pads”. Virtually all live in social communities, while some prosimians are solitary. The females are more tolerant of each other than in prosimian groups. Groups are stable over generations, regardless of the deaths of individuals, while ape groups may break up upon a leader’s death, or change composition at times. Generally, male monkeys must leave the group upon adulthood. There are four families of monkeys, two Old World families and two New World families. APES Unlike prosimians and monkeys, apes have no tail, and little or no ischial callosities. They have no claws, only flat nails, on their digits. Thumbs and big toes are very opposed. Forelimbs are longer than rear limbs. Noses are flat and they have no muzzle, although the jaw protrudes. Shoulders rotate for full brachiation, but overall the body is thicker and does not bend as much as monkeys’. Groups may not be stable over generations. Social organization is looser, probably because they have less need for group defense. There are two families of apes, both in the Old World. EVOLUTION OF THE ORDER The fossil record indicates that primates have been around for some 70 million years. The earliest primate diverged from a primitive form of insectivore at a time when many of the placental mammals were in their incipient stages of evolution. The taxonomy of the primates today includes several grades (a grade is composed of animals that share an evolutionary past and today share similarities in anatomy and behavior). The variety of living forms within the primate group actually reflects the different stages of primate evolution. Although there have been numerous species extinctions along each line, there is at least one and usually many representative types of each grade still in existence today. The early lemur- like creatures provided the ancestral stock for the next grade of primate evolution, the tarsiers. Some forms of lemur, however, continued to evolve as lemurs. Once again, each grade in primate evolution provided the evolutionary foundation for the next while, at the same time, each grade also produced animals which continued to evolve within the grade each grade also produced animals which continued to evolve within the grade (Fig. 1). For us, one of the key advantages of displaying a variety of primates in a zoo collection is that they reflect the images of the past. This is an incredible asset when planning an education program for the public. Figure 1: the evolution of the modern primates. The designations A, B, C, etc., refer to grades. A grade is typically composed of many species, which share a common origin. The members of a grade are usually similar in general appearance and behavior. EVOLUTIONARY GRADES OF THE ORDER PRIMATA Tree Shrews The tree shrews of Southeast Asia may be similar to some of the very earliest primates after the divergence from the insectivore group. The tree shrew is a small, arboreal creature with a long snout, claws on the digits, and eyes on the side of the head. The overall physical appearance of the animal is not what you would expect for a primate. Some scientists, however, have suggested that they be included in the Order based on a few internal anatomical similarities. Regardless (as one author put it, the tree shrew doesn’t care), this small Asian animal presents in physical appearance, behavior, and interaction with the environment a very good image of what the original primate was like. Lemurs & Lorises From the original primate group there evolved a large number of primates of the next grade, (lemurs & lorises). During the Eocene, 40 to 50 million years ago, there was a temporary reversal in the cooling trend, which had contributed to the large number of reptilian extinctions in the Mesozoic allowed the tropical forest to once again expand. Early primates among other life forms radiated to fill many of the arboreal niches. There were many more species of lemur and Loris during the Eocene than presently exist. Most of these forms ended in extinction while others continued to evolve to the present time. The ancestral stock of modern day lemurs came to live on the island of Madagascar off the African coast. The competition in an island ecosystem is often less intense as there are fewer types of animals trying to make a living. In this case, the lemurs diversified to fill a number of niches. Some are nocturnal while others are diurnal. Some are highly social while others are solitary. Some are arboreal in their habits while others spend more time on the ground. Most are relatively small, but a recent extinct form of lemur may have weighed more than 100 pounds. The diversity displayed by the lemurs does not take away from their basic nature as primates. Closely related to the lemurs are the lorises. Today they are located in the forests of Africa and the Far East. They all are nocturnal, thus avoiding much of the competition for food and space by diurnal forest dwellers.