Primates are a recognized Order of extant
mammals. This ancient group, whose origins go back to the very
earliest mammals, is so diverse that it defies simple summary
or simple definition. When we compare modern forms to fossil species,
criteria that identify extant species often excludes possible
ancestral fossil taxa. One solution to this dilemma is to list
general characters that are progressively more evident in younger
species, realizing that these attributes are not necessarily present
in more ancient primate lifeways. Thus St. G. Mivart (1873) defined
the primates as:
"Unguiculate claviculate placental mammals, with orbits encircled by bone; three kinds of teeth, at least at one time of life; brain always with a posterior lobe and calcarine fissure; the innermost digits of at least one pair of extremities opposable, hallux with a flat nail or none; a well-developed caecum; penis pendulous; testes scrotal; always two pectoral mammae."
Le Gros Clark (1959) defined the Order
Primates as a natural group of mammals distinguished by nine general
features. These features generally become more noticeable in recent
primates so they are described as trends, that is, anatomical
directions in which primates (as a group) diverged from other
mammals. Some primate species do not have all of these characters,
but they become more common as the primate order diverges from
its ancient mammalian antecedent:
1. They possess a generalized limb structure. Examples include basic pentadactyly (five digits) and retention of bones (such as the clavicle) often lost in other mammals.
2. Mobile digits, especially the thumb and large toe.
3. Flattened nails and tactile pads occur at the end of digits.
4. Reduced muzzle size.
5. Binocular vision.
6. Less emphasis on the sense of smell.
7. Simple cusp pattern of molars and a general reduction in number of teeth.
8. Expanded and elaborated brain, especially the cerebral cortex.
9. Longer gestation and increased vascularization of placental membranes.
More recently, Martin (1990, page 641)
provide a revised list of characters usually seen in extant primate
species:
1. The hallux is well developed, divergent, and bears a flat nail.
2. The distal segment of the calcaneus is elongated relative to body size.
3. Orbits are relatively large and convergent. The interorbital distance is relatively small. A postorbital bar is present.
4. There is relatively prominent auditory bull, the ventral floor of which is formed from the petrosal.
5. The braincase is relatively large and an endocast, if available, reveals a Sylvian sulcus.
6. The maximum dental formula is I2C1P3M3. The premaxilla is short, upper incisors are arranged more transversely, molars have low rounded cusps, and mandibular molars have enlarged talonids.
7. They typically inhabit tropical or subtropical forest habitats.
A primatologist uses the comparative
method to place humanity in a zoological perspective. There is
a presumption of biological continuity, with mankind being only
one species among many in the Order Primates. Evolutionary processes
have sculpted primate biology into many niches and species by
modifying existing anatomies and behaviors. A survey of Primates
thus becomes a description of a gigantic natural experiment in
which details of adaptation reveal processes that shape and control
our biology. Knowledge becomes an axe that cuts away myth and
superstition about ourselves, and in a world in which remaining
fragments of ecosystems where our ancestors evolved grow smaller
by the hour, we must look quickly at our primate relatives or
forever lose the chance (return
to outline) .
Generally the Order Primates is composed of a very diverse group of related lineages. The following table outlines a classification for living Primates usually seen in textbooks and older publications. It was based on traditional systematic thinking and groups primates into Prosimians (lifeways and anatomies older than simians), anthropoids (human-like), and hominids (humans).
An alternate taxonomy is influenced by data from molecular biology and cladistics. The latter represents slightly different thinking about phylogenetic relationships, but the older classification contains vocabulary used in most of existing scientific literature. Since science is an open system with changing vocabularies, one must expect modifications, but the price of change is that a reader must take care to avoid confusion when moving from one text to another. Sometimes one must compromise between accurately reflecting the newest hypotheses about phylogeny and effective use of language for communication.
The two taxonomies differ on the placement of a single primate family, Tarsiidae, the tarsiers. In the tradition of Simpson (1945), groups the tarsier with the Prosimians and is the vocabulary used in this text.
The alternate classification system places
Tarsiers with the anthropoids. In this alternate taxonomy, living
primates are divided into semiorders Strepsirhini and Haplorhini
on the basis of differences in the placenta, external nose (and
upper lip), eye, middle ear, and path of olfactory nerves. "Strepho"
means "turned inward" and "rhinos is "nose"
(in Greek) (return to outline).
Strepsirhines have a moist, glandular area around the nostrils (the rhinarium), a division or gap in the superior border of each nostril, and a divided upper lip attached to gums by a membrane (the philtrum), and a separation between the upper central incisors. The rhinarium bears an extension of the olfactory skin of the nasal passages and is very sensitive to smell and touch. The strepsirhine eye has a tapetum lucidum, a layer of reflective tissue behind the retina which reflects light back toward the pupil, making the eyes of nocturnal mammals visible when caught by a spotlight in the dark or by the flash of a camera. All Strepsirhines have a modified nail resembling a claw on the second pedal digit, the grooming digit.
Mesial mandibular teeth (canines and
incisors) project forward to form a dental comb in all species
except the aye-aye. These specialized teeth are slender, elongated,
and procumbent. A hardened structure on the tongue, the sublingula,
removes debris from the dental comb. Strepsirhines as a group
retain a highly developed sense of smell that plays important
roles in their social behaviors. For example, their territories
and ranges are usually scent-marked, a process that appears to
identify both identity and hormonal condition of the resident(return to outline).
"Haplo" means "simple"
in Greek. The rhinarium of a haplorine is dry, nostrils are more
rounded and continuous, and the upper lip is not divided by a
philtrum. The reduced medial attachment of the lip allows freedom
of movement. Haplorhine eyes lack a tapetum and do not reflect
noticeable amounts of light back through the pupil. Paleontologists
generally do not use this Strepsirhini/Haplorhini classification
since it relies on soft tissues not usually represented in fossils
(return to outline).
Prosimians generally retain certain primitive cranial features, particularly lack of union of the metopic suture of the frontal bone and the symphyseal suture of the mandible. The orbit is enclosed by a ring of bone formed by a process from the frontal and zygomatic bone, but the back of the orbit is open. Most prosimian families have a dental comb. Except for Daubentonia, prosimians have flattened nails on all digits except the second pedal digit, which bears a compressed nail, a grooming digit.
Most prosimian species come from the world's fourth largest island, Madagascar. Geologically, Madagascar separated from East Africa about 100 million years ago. The plants and animals that managed to establish themselves on the island, protected by the Mozambique Channel and the Indian Ocean from the flora and fauna of Africa and Asia, are among the most unusual on Earth. Madagascar has more endemic species, species found nowhere else, than any other major land area in the world. (return to outline).
Chiromyiformes is represented among living primates by a single species, Daubentonia madagascariensis Gmelin, 1788, commonly known as the aye-aye. The aye-aye is an extraordinary animal that occupies the ecological niche of a woodpecker. That is, it searches for wood-boring insects, gnaws an opening in the bark, and digs out insects or larvae. Like a beaver, it has severe dental attrition on its wood chewing procumbent mesial teeth, the roots of which are enlarged and continuously growing, and pass underneath the roots of other teeth. These continuously growing incisors have enamel on only one surface. Excessive wear from gnawing wood keeps them sharp and correctly proportioned. The other teeth are greatly reduced in number, producing a dental formula of 1 0 1 3/1 0 0 3. All digits end in compressed, claw-like nails except the first toes, and the third finger is especially long and thin. After an insect larva is exposed, it is fished from its burrow with this specialized on the third finger, a "foraging digit" . Its diet includes various fruits, including coconuts The aye-aye is a large prosimian with a total body length (head, trunk, and tail)head and body length about a meter in size.
The aye-aye builds nests high in the
trees of coastal lowland rain forest areas (below 200 m elevation)
along the eastern and northern margins of Madagascar. Unfortunately,
these forests have been virtually eliminated by human activities.
The Duke University Primate Center is attempting to establish
a captive breeding program that can be used to supply animals
for reintroduction to forest reserves in Madagascar (return to outline).
Like Daubentonia, Lemuriformes are found
only on Madagascar. All Lemuriformes have a mandibular dental
comb, Although they exhibit a variety of social systems, Lemuriformes
generally have very brief mating seasons (a few days).
Indriidae are unique among lemuroids in terms of diet and locomotion. The are somewhat folivorous and have an enlarged digestive tract to process plant materials, usually leaves, shoots, fruits, flowers and bark. They are also vertical clingers and leapers that emphasize the hind limb's role in locomotion. Their dental formula of 2 1 2 3/1 1 2 3 has fewer premolars and incisors than does that of the Lemuridae. The family Indriidae includes three genera, Indri (indris), Avahi (wooly lemur), and Propithecus (sifaka) with intermembral indexes of 63, 57, and 58 respectively.
Indris, the largest form in this family
with a body weight of about 6 kg, has only a vestigial tail. Most
other arboreal leaping primates use the tail to assist in controlling
body position during a leap. Nocturnal wooly lemurs are much smaller,
weighing about 1 kg. Sifakas, the most numerous representatives
of this family, range in size fro 4 to 6 kg (return
to outline).
The Family Lemuridae includes three very diverse subfamilies, Cheirogaleinae, Lepilemurinae, and Lemurinae.
Subfamily Cheirogaleinae
There are five genera in this subfamily;
Microcebus (mouse lemurs),
Mirza (Coquerel's mouse lemur),
Cheirogaleus (dwarf lemurs),
Phaner (forked lemurs), and
Allocebus (hairy-eared dwarf lemurs).
Cheirogaleids are very small nocturnal nest-builders. Microcebus (mouse lemurs) usual body weight of 60g makes it the smallest of the Lemuriformes. The other Cheirogaleids are much larger, ranging from 300 to 450g. Allocebus is poorly known and was thought to be extinct until recently.
Cheirogaleid diets emphasize relatively nutritious foods -- insects, flowers, gum, fruit and pollen. They store fat in their tails during wet seasons when food is more plentiful and subsist in part on stored fat during dry seasons. At least one group (Cheirogaleus) appears to hibernate through part of the dry season. Gestation periods are brief (60-70 days) and the young (twins or triplets) are "parked" in the nest while the mother forages.
Social behaviors of cheirogaleids are complex. Generally male adults have ranges that overlap the ranges of one or more adult females, a pattern called a noyau social system. Some Microcebus groups include cooperating adult females who sleep together in a community nest.
In contrast, Phaner lives in small permanent
groups, often one male and one female. Only a single infant is
born. Although they establish a nest in a tree hole, the infant
is carried on the mother's abdomen during foraging. Phaner diets
emphasize gummivory. Digital pads on fingers and toes are enlarged
behind fingernails that are compressed into squirrel-like claws.
An unusual feature of Phaner is caniforme upper first premolars,
that is, the premolars are modified into a long canine-like structures
(return to outline).
Subfamily Lemurinae
The Lemurinae include the genera Lemur, Varecia, Hapalemur, and Eulemur. All share the dental formula 2133/2133. These are the best known Malagasy lemurs. They are generally diurnal primates with large body sizes (2 to 4 kg) and longer gestation periods (100 -135 days).
Ring-tailed lemurs (Lemur catta), familiar to zoo visitors, are the most terrestrial strepsirhines, spending more than a third of their day on the ground. They form bisexual groups of 15 to 20 individuals that defend large territories (5-10 ha). Troops have status hierarchies and adult females are dominant over adult males.
The other Lemurinae are more arboreal. Eulemur are unusual in that they are sexually dichromatic, that is, males and females have different color patterns. Mongoose lemurs, Lemur mongoz, are sometimes nocturnal, and are generally found in small groups, often one male and one female and their young. Similarly, variegated lemurs, Varecia variegata, are thought to be monogamous.
Hapalemur specializes in bamboo and can
subsist on the stalk, leaves and shoots. These diurnal, vertical
clinging and leapers climb quadrupedally. Some species produce
a strong scent from a neck gland that permeates the surrounding
vegetation. Golden bamboo lemurs, Hapalemur aureus, eat the growing
tips of a bamboo species that is known to contain substantial
amounts of cyanide, consuming a quantity of cyanide daily that
would be lethal to other primates (Glander et al., 1989) (return to outline).
Family Megaladapidae
Subfamily Lepilemurinae
The weasel lemur, Lepilemur mustelinus,
sometimes called the sportitive lemur, is the only species in
this subfamily. They are relatively folivorous and have a large
caecum. They lack upper incisors and are reported to have noyau
social systems. Locomotion emphasizes arboreal vertical clinging
and leaping and bipedal hopping on the ground. Systematics of
this group is problematic with perhaps as many as seven species
differentiated by chromosome variation (return
to outline).
Infraorder Lorisiformes
Lorisoidea is differentiated from Lemuriformes by the details of arterial circulation and structure of the auditory region. The Prosimian infraorders differ in the pattern of branching of the internal carotid artery. The central and posterior parts of the tympanic roof are pneumatized (inflated), expanding the mastoid bone medial to the auditory bulla. Their dental formula is 2133/2133 with the lower incisors and canine participating in the dental comb (return to outline).
Subfamily Lorisinae
The Lorisinae consists of two African forms, Perodicticus (potto) and Arctocebus (angwantibo), and two Asian forms Loris (slender loris) and Nycticebus (slow loris). On each continent there is a thin slow-climber (Loris or Arctocebus) weighing about 300g and a heavier form (Nycticebus or Perodicticus) weighing about 1000g. There is also a diminutive form of the slow loris, the pygmy slow loris (Nycticebus pygmaeus) with a body weight of 300g. All Lorisinae are nocturnal, arboreal, slow-moving climbers of dense tropical forests. The first lower premolar (Pm2) resembles a canine and has a single root. The small slender loris has a very narrow pelvis with a permanently open (unfused) pubic symphysis. Gestation is relatively long for prosimians (131-136 days for the angwantibo, 160-170 days for the slender loris, 193 days for the potto). Births are usually single, and the mother may hide or "park" an older infant in vegetation while she is foraging. Growth is rapid, reaching sexual maturity in less than two years.
They feed on flowers, fruits, insects, and small vertebrates. Locomotion is deliberate quadramanual climbing with snake-like undulations in the vertebral column. Arms are almost as long and well muscled as legs. The Intermembral index ranges from 88 to 91 for the various species. The second finger is reduced to a short stub but a powerful grip is formed with the first and third digits. The tail is short. Hands and feet have extremely opposable digits and progression is cautious, usually not releasing the grasp of one hand until the other is securely placed. They depend upon stealth as a primary means of avoiding predation and can remain motionless in a tree with the head tucked between the arms. In this posture, it is difficult to distinguish the animal from tree structures. When necessary however, a loris can move quickly and its extremely flexible joints and back allow an unusual range of fluid motion.
At times, the slow loris emits a pungent odor. Isolation of toxins from the brachial gland exudates indicated that this loris is protected from predation by being toxic and posses a dangerous bite. Some Lorisinae emit strong odors during estrus.
The potto, Perodicticus potto, an inhabitant of African forest canopy, has an unusual defensive mechanism. Since it is not a leaping form and frequently uses exposed arboreal pathways along tree branches, one might expect it to be easy prey to arboreal predators. In this environment, a mammalian carnivore must approach the potto along the same pathway, and the potto has an unusual defense. The third to ninth cervical vertebrae have enlarged spines, the largest of which protrudes from under the skin of the back and neck. The skin around this area is modified into a scapular shield, an area of cornified (hardened) skin in the scapular region that is very thick, covered with tactually sensitive guard hairs and exceptionally richly supplied with nerve endings and tactile corpuscles. The potto thus has a very durable, but very sensitive shield on the shoulders and neck. When confronted with a mammalian predator, the potto assumes a defense posture in which its limbs are tensed, hands and feet are brought close together with all four extremities gripping the branch tightly, head is tucked between arms, and chin pulled against its chest so the head is fully protected by forearms. The sensitive but durable scapular shield is presented to the attacker, who has few possibilities to maneuver in the approach along the tree branch providing the arboreal pathway. The moment the predator contacts the scapular shield, the potto uses the shield as a battering ram to dislodge the aggressor from the branch. Since the potto's firm grip provides a more firm attachment to the branch than that of most predatory mammals, the predator risks being knocked from the tree. Of course the potto does bite if the intruder does get past the scapular shield. If the predator is too large, or is a snake, this shield defense is not effective and the potto simply bails out by leaping off the branch and falling to another branch or to the ground.
Social behavior among the Lorisinae is best known for the potto. A male potto 's home range usually overlaps the ranges of several females. Adjacent female ranges may overlap. Daughters sometimes acquire the mother's ranges, forcing the mother to move, but sons leave their natal range. Presumably they are very mobile until they are mature enough to establish a range of their own (return to outline).
Subfamily Galaginae
The bushbabies, sometimes called galagoes, are nocturnal, vertical clinging and leaping animals of the woodland savannah areas of subsaharan Africa. They are represented by four genera, Otolemur, Galago, Galagoides, and Euoticus. Their elongated and muscular hind limbs are reflected in the intermembral indexes which ranges from 52 to 70. Most bushbaby species can execute vertical leaps exceeding two meters. Hands and feet have large tactile pads which are moistened with urine (urine washing) to increase finger pad adhesion to branches and to leave a urine scent message. The needle-clawed bush baby (Euoticus) has a ridge down the center of each fingernail that extends beyond the nail as a sharp projection. Bushbabies are generally small animals with most species ranging from 100 to 200g body weight. The two species of greater bushbabies (Otolemur) have reported body weights of 700 and 1800g.
Typical bush baby diet includes invertebrates,
small vertebrates, flowers, fruits, and gums. Several adult females
share home ranges and sleep in the same day nest in a tree hollow
or dense foliage. Gestation is about 120 days and the immature
young are left in the nest or parked in a hidden place while the
mother forages. Young that are too immature to cling are carried
in the mother's mouth. Growth is rapid and sexual maturity is
reached in less than a year (return
to outline).
The Infraorder Tarsiiformes is represented by a single genus, Tarsius. Tarsiers are small (body weights slightly over 100g) vertical clinging and leaping primates in the shrub and forest understory in the Philippines, Borneo, and Sumatra. Diets consists primarily of invertebrates and small vertebrates. Teeth are large for body size and the dental formula is 2133/1133. The sense of hearing is well developed. The enlarged auditory bulla is connected to an external auditory meatus by a bony tube.
Part of the anthropological interest
in the tarsier is its unique combination of prosimian and anthropoid
traits. A partial list includes:
Prosimian Anthropoid
metopic suture partial postorbital closure
unfused mandibular symphysis lack of tapetum
grooming claws teeth large for body size
bicornuate uterus haemochorial placentation
external auditory meatus
no nasal rhinarium
no stapedial artery
Other unusual anatomical characteristics include a non-opposable thumb, fusion of the tibia and fibula, and toilet claws on the second and third digits of the foot. Their most distinctive features are the eyes, largest relative to body size among primates. Even though orbits are dramatically enlarged and are surrounded by a bony flange like rim, the eye is so large more than half of it protrudes beyond the orbit. The eyes are immobile in their orbits and the Tarsier must change its field of vision by moving the head. Therefore the neck is extremely mobile, permitting the animal to look almost directly backwards. The quickness and mobility of head movements during visual tracking sometimes give the impression that the animal can swivel its head 360o. Perhaps one reason for the enlarged eye is that this nocturnal primate lacks a tapetum lucidum to reflect light back toward photoreceptor cells.
Tarsiers are exceptional leapers, crossing forest gaps greater than 6m. The hind limb is robust and muscular with an intermembral index of about 50. Tibia and fibula are fused for strength and some of the ankle bones (talus, calcaneus, and navicular bones) are greatly elongated. The fused tibia and fibula make a very stable ankle joint and the elongated tarsals provide a powerful lever for jumping in the ankle joint.
Socially, tariser groups usually
consist of mated pairs and their young. Territories are scent-marked
and announced by vocal duetting by both male and female. Gestation
is 180 days and a single infant is born. The mother transports
the infant for the first few weeks by holding it in her mouth,
parking it on a nearby branch while she forages (return to outline).
The second suborder of primates,
Anthropoidea, consists of the platyrrhine monkeys of the Americas,
the catarrhine monkeys and hominoids of Africa, Asia, and Europe,
and the hominoidea, extant apes and humans. Anthropoids are characterized
by:
- The orbit is closed posteriorly by an extension of the frontal, zygomatic and sphenoid bones.
-Orbits orient forward (stereoscopic vision is well developed).
-The sense of smell is de-emphasized with reduction in the bones of the nasal region such as the turbinates.
-The lacrimal bone is positioned within the orbital cavity.
-The two halves of the mandible fuse early in maturation.
-Likewise, in most individuals, the metopic suture unites early in life, forming an unpaired frontal bone.
-Anthropoids have spatulate and relatively vertically set incisors.
-Molars and premolars are bunodont (rounded) except for Pm3.
-In some species Pm3 has a blade-like (sectorial) articulation with and enlarged upper canine.
-The tympanic ring is fused to the auditory bulla.
These are the primates of the Americas.
Ceboidea, the primates of the New
World, are a very diverse group that presumably evolved parallel
to the monkeys of the Old World from a very early anthropoid precursor.
They have platyrrhine (flat) noses produced by flaring cartilaginous
nares and broad nasal septa. Their primitive dental formula is
2133/2133, that is, they retain three premolars on each quadrant
of the jaw. The tympanic ring is fused to the auditory bulla,
but it does not form a complete bony tube (return
to outline).
This platyrrhine family is characterized
by a trend toward smaller third molars, large broad premolars,
large canines, and short faces. Members have flattened nails on
all digits. Some Cebidae have prehensile tails that serve as a
fifth hand for grasping and manipulation.
Subfamily Cebinae
Capuchins (Cebus) and squirrel monkeys (Saimiri) are frugivores and insectivores. Both have an enlarged rounded braincase that produces a relatively central foramen magnum.
Capuchins are found in a wide variety of forests, from mangroves to mountain rain forests of Central and South America. They have a flexible and muscular back with short powerful arms (intermembral index of 81) and a prehensile tail strong enough to support their full weight. Their diet consists of fruit, leaves, insects, small vertebrates, and nuts. Much of their foraging time is spent gleaning insects from foliage, dead leaves, bark, and dead branches. Capuchins are skilled at breaking dead branches, peeling bark, and unrolling leaves in a search for insects. They are adept at opening hard nuts and have extraordinarily thick enamel on their teeth. Dead branches are used as missiles to discourage terrestrial predators, particularly humans and snakes. Snakes and birds of prey are major predators on capuchins, and these monkeys have elaborate alarm calls to alert each other to danger. The snake alarm in weeper capuchins specifies the relative location of the snake, that is whether it is one ground or in a tree (Norris, 1990). Primatologists who shadow capuchins appreciate the animals' diligence in warning everyone about poisonous snakes on the ground. A gestation period of 190 results in a single birth. Maturation is slow -- physical maturity is reached in seven years for males, but females can reproduce after four years. Adult body weights are about 3 kg for males and 2 kg for females. Capuchins form multi-male, multi-female groups and are known for their gregarious nature, intelligence and manipulative skills.
The squirrel monkey, Saimiri, occurs in intermediate levels of most South American tropical rain forests . Smaller populations are found in Costa Rica and Panama. They forage on flowers, fruits, and insects. They are flush hunters, that is members of the group catch insects and small vertebrates that take flight from movements of other monkeys in foraging parties. They also spend much time gleaning insects from vegetation. Adult females (700g) are smaller than adult males (1000g). The tail is not prehensile and locomotion is primarily quadrupedal climbing and jumping along tree limbs or lianas. Though the gestation period is 180 days, only 10 days shorter than that of capuchins, the small bodied squirrel monkeys mature more rapidly. Females are able to reproduce after 2.5 years. Squirrel monkey males undergo physical and behavioral changes as the mating season approaches. They gain weight, especially on the upper trunk, arms, shoulders, and neck, and produce viable sperm only during the three or four months of sexual activity.
Squirrel monkeys are highly social.
Groups of 200 or more are reported for the Amazon basin, but social
group sizes of 20 to 35 are probably more typical. Troops subdivide
into adult male, mother-infant, and juvenile subgroups. Female
subgroups are extremely social and responsive to changes in group
composition. Except for Monkey Jungle, a commercial exhibitor
of monkeys in Florida, early attempts to raise squirrel monkeys
in captivity were foiled by the animals' sensitivity to manipulations
(return to outline).
Subfamily Alouattinae
Howler monkeys, Alouatta, should properly be called roaring monkeys, for their loud vocalization bears little resemblance to the howls of dogs or wolves. All howlers have a greatly enlarged hyoid bone that serves as a resonating chamber and allows their unique call. Males, with their larger body sizes (7.5 kg versus about 5.7 kg for females), have larger hyoids and produce lower pitched sounds. Locomotion is quadrupedal and assisted by a very prehensile tail. Gestation is 180-195 days, and births are usually single. The infant clings to the mother for transport.
Howlers are folivores, consuming
leaves, flowers, and some fruits. They are selective feeders,
focusing upon young foliage or vegetation that is relatively palatable.
They have an enlarged caecum where microorganisms help break down
the cellulose content of their diet. Howler life styles seem to
focus on gut-management, that is, they carefully select food items,
and after feeding, spend much time resting and allowing meals
to be digested. Howlers live in groups of 6 to 20 individuals
with generally more adult females than adult males in the group
(return to outline).
Subfamily Atelinae
Atelinae includes three genera, spider monkeys (Ateles), woolly spider monkeys (Brachyteles), and woolly monkeys (Lagothrix). This subfamily is unique among primates in having the greatest use of the tail as a prehensile and tactile organ. Spider monkeys and woolly spider monkeys are noted for very rapid arboreal locomotion. They literally run, jump, and swing through the trees using all five appendages. In keeping with their pattern of locomotion, Atelinae have very elongated arms, legs and tails with an Intermembral Index of 105. The muscular tail is particularly long (about 820 mm versus a head and body length of 560 mm). Hips and shoulders are extremely flexible. The elongate fingers and very reduced thumbs are effective for hooking branches during rapid suspensory locomotion. This differs from arm swinging (brachiation) because all five appendages are used. Though much of the functional anatomy of the arms and hands are shared with other primates that brachiate, the very mobile hip of spider monkeys allows the feet to grasp footholds above the animal's head. Rapid suspensory locomotion that utilizes all four limbs and a prehensile tail is called New World semibrachiation. Without an opposable thumb, spider and wooly spider monkeys rely of the tactile and flexible tail to pick up and manipulate small objects.
These extraordinary leapers use branches as springboards to launch themselves across tree gaps exceeding 12m. They also do not hesitate to drop from the canopy into densely growing understory. Juvenile spider monkeys sometimes make sky diving a game, leaping from the canopy into the chablis produced by a tree fall, free falling more than 20m, and landing with all five appendages outstretched in the springy secondary growth. They then scramble quickly to the canopy to repeat the game. With five very mobile and prehensile appendages, spider monkeys are superb suspensory feeders, able to exploit all of a tree's canopy.
The long and pendulous clitoris of females is more visible to a casual observer than the scrotum and penis of males. As a result, inexperienced observers may confuse the genders. Although body sizes overlap, female means for body dimensions slightly exceed those of males.
Group size varies with locality and habitat; from one-male groups of five or six animals in southern Mexico to more than sixty individuals in multimale multifemale groups in Guatemala. These highly social groups exhibit strong dominance relationships effecting both genders and result in high rates of within group aggression. Lower ranking animals are supplanted from feeding trees by aggressive higher ranking individuals. Spider monkeys are often territorial, depending upon male aggression to turn away intruders.
Spider monkeys readily travel long
distances (several kilometers) to forage each day. The group fragments
into foraging parties that keep in contact by vocalizing above
the canopy (return to outline).
Subfamily Aotinae
Night monkeys (Aotus) and titi monkeys (Callicebus) are small (about 1 kg), quadrupedal leaping monkeys with an Intermembral Index of 74. Their mainly frugivorous diet is supplemented with insects. Gestation is 133 days and births are single or twin. The father caretakes and transports infants.
The night monkey (also called the
owl monkey), is the only nocturnal anthropoid. Its coneless retina
bears a fovea, suggesting a recent diurnal ancestry. Aotus is
found throughout the mainland continental forests from Panama
to Paraguay and Argentina. It sleeps in hollows or day nests in
dense vegetation and forages on insects, leaves, and fruit. Social
groups usually consist of a mated pair and young (return to outline).
Subfamily Pitheciinae
The Pithecinae, sakis (Pithecia and Chiropotes) and uakaris (Cacajao), are frugivorous with unusually robust and laterally displaced canines adapted to opening tough seeds and fruits covered by tough pods. Their enlarged canine and wide nose produces a relatively flat face. Pitheciines walk and run quadrupedally on larger branches, but they are particularly adept and bounding and bipedal jumping. They are reported to jump across forest gaps as wide as 10m. The hind limb is large and muscular (Intermembral Index ranges from 75 to 83). Their bushy tail is not prehensile. Body weights range from 2 to 3 kg. Usually seen in small groups, some species (such as the white-faced saki, Pithecia pithecia, are perhaps mistakenly reported to be monogamous.
The white-faced saki is sexually
dichromatic. Males have black body hair and a white fringe of
hair around the face. Females are gray-brown. The hairless, brilliantly
crimson face and crown of the bald uakari (Cacajao calvus) is
striking (return to outline).
Subfamily Callithricinae
All callithricines, expressly Goeldi's monkey (Callimico), marmosets (Callithrix and Cebuella), and tamarins (Saguinus and Leontopithecus), are small-bodied (100g to 700g body weights) colorful primates with very reduced molar cusp patterns. They have compressed claw-like nails on all digits except the big toe (first pedal digit) which bears a broad flat nail. The two tamarin genera have a lower canine tooth that projects markedly. In contrast, marmoset mandibular canines are about the same length as incisors and join the incisors to form a sort of slightly procumbent dental comb that is used to gouge holes or scars in the bark of trees for gummivory. Except for Callimico, Callithricidae have a reduced dental formula of 2 1 3 2/ 2 1 3 2. Furthermore, the molar cusps are reduced to three rather than four major cusps. Callimico retains three molars and a reduced fourth cusp (hypocone).
Callithricines, often described as primarily insectivous, feed on insects, fruits, flowers, leaves, plant exudates (sap or gum), and small animals. Marmosets emphasize gummivory. Tree scars are scent-marked and repeatedly visited to harvest tree exudates.
Members of this subfamily live in
small family groups and adults of both sex, in addition to the
mother, provide care and transport to infants. Except for Callimico
which has single births, twins and triplets are common. It is
usual for a male parent to transport infants, with the mother
retrieving infants for nursing. Infants grow rapidly and adult
body size is small. Pygmy marmosets (Cebuella pygmaea), found
in the upper Amazon basin, are the smallest of the New World monkeys
(125g). Despite their small body size, most callithricines are
extremely aggressive and territorial. A small marmoset family
may occupy a territory that extends over several hectares of forest
(return to outline).
Catarrhines, the extant Old World
anthropoids, are traditionally divided by scientists into two
superfamilies, the Old World Monkeys (Cercopithecoidea) and the
hominoids (Hominoidea). Old World anthropoids generally share
a single dental formula: 2.1.2.3./ 2.1.2.3.. Most species exhibit
a specialized mechanism to sharpen the tip of the upper canine.
A sectorial Pm3, a single-cusped bilaterally compressed Pm3, hones
against the distal lingual surface of the upper canine. Similarly,
the mandibular canine hones against the mesial surface of the
same upper canine. The honing effect is marked enough to repoint
a canine that is broken near the tip. The auditory ring is elongated
into an ossified tube that ends in tubular external auditory meatus
(return to outline).
The Old Work monkeys (Cercopithecoidea) are recognizable by their bilophodont molar teeth, a dental adaptation that permits effective slicing of leaves or grass stems even under conditions of extreme tooth wear. Bilophodont molars have a transverse crest between molar cusp pairs. Molars one and two are reduced to four cusps, each bearing a constriction between the mesial pair of cusps and the distal cusp pair. The combination of transverse crests and mid-tooth mesial-distal constrictions produces two lophs.
Although the character is not confined
to cercopithecoids, members of this superfamily have an ischial
callosity, a hairless, fleshy pad on the ischial tuberosity
(a flared surface on the ischial portion of the coxa). These ischial
callosities are sitting pads that allow comfortable sitting on
small branches. Since they are hairless, they sometimes exhibit
color changes and serve as part of the animal's hormonal display
(return to outline).
Subfamily Cercopithecinae
This subfamily of Old World Monkeys is primarily omnivorous, foraging on seeds, fruits, insects, and small animals. An emphasis on concentrated nutritious food items is reflected by the presence of cheek pouches, buccal pouches surrounded by fibers of the buccinator muscle. There is a natural weakness between the muscle units and a pocket is formed by forcing objects into the cheek. Cheek pouches can be greatly distended with use. When the pouch contains objects or food, the animal may push externally on the cheek with its hand to retrieve a particular item back into the mouth.
Cercopithecines are a diverse and successful subfamily, occupying niches and habitats widely distributed over Africa and Asia. Six general are usually recognized: Cercopithecus (African guenons), Cercocebus (mangabeys), Macaca (macaques), Mandrillus (drill and mandrill), Papio (savannah baboons), and Theropithecus (gelada baboon).
African guenons represent one of the few examples among extant primates whose radiation is recent enough to reveal the variety, subtlety, and beauty of that event. Their diversity is not represented by a few survivors in relic niches, rather they are an evolutionary bouquet of amazing variation, a remarkable array of varying anatomy, karyotype, vocalization, locomotion, niche, and behavior. The diploid chromosome number varies among the guenons, but it is always greater than 54. The other cercopithecines have a diploid chromosome number of 42. Rowell (1988) lists four common features of guenon social systems:
1. They tend coordinate and adjust their movements by monitoring the actions of their neighbors with relatively little use of overt contact or gestures. This is particularly notable if we consider the difficulty of maintaining visual contact in a canopy where foliage obscures vision, and where light and dark contrasts handicap visual discrimination.
2. Social groups which include adult females usually contain only one central adult male except during mating seasons. Other males may associate with the group, but they avoid close proximity to the main troop, which consists primarily of females and immatures.
3. Groups of females establish and defend territories.
4. Male guenons interact relatively little with adult females and are not dominant to them.
The patas monkey (Cercopithecus patas) is the most terrestrial of guenons, and is one of the most terrestrial primates. It inhabits open grasslands and marginal areas of savannah woodlands, avoiding predation primarily by camouflage, stealth, and vigilance. Its reddish pelage blends into the predominantly red African soils. Adult males perform decoy and defensive behaviors. Male patas monkeys, capable of sustaining running speeds of 50 km per hour, are unique among nonhuman primates. Even though some mammalian predators can manage short dashes of more than 100 km per hour, no predator on the African savannah can outrun an adult male patas except in ambush. Patas anatomical specializations for running include a linear dog-like profile, digitigrade hands and feet, and an enlarged thoracic cavity similar to that of a greyhound or other racing breed of dog. The female is quite dimorphically smaller, similar in size to other guenons.
The male patas monkey performs a role of vigilance and decoy. When a troop approaches a dangerous area, such as a water source (ambush predators find water sources convenient places to hunt), the male approaches first and is not joined by the group until he finds it safe and proceeds to drink. If a predator is encountered in a context dangerous to the troop, the male may run near the predator in a conspicuous display. If the predator gives chase, the male runs just fast enough to maintain a safety margin against a sudden dash by the hunter as pursuit lures the danger away from the troop. Ordinarily, patas monkeys depend upon the general guenon characteristic of "freezing," remaining very still, invisible to potential predators. Like other guenons, patas monkeys may sleep in trees at night for protection, but unlike other guenons, patas sometimes disperse and sleep on the ground if appropriate sleeping trees are not at hand. Patas monkeys forage throughout the grasslands eating seeds, shoots, fruits, berries, gums, and beans from savannah grasses shrubs and trees. The troop disperses widely in relaxed circumstances so that adjacent individuals are sometimes out of sight of each other. Troops are territorial and their home ranges often exceed 5,000 ha. Patas day ranges are second in size only to humans among primates.
In contrast, the talapoin monkey (Cercopithecus talapoin), the smallest cercopithecoid at about 1 kg, lives in riverine forests of Central Africa. Extremely adept at swimming and jumping, they are known to escape predators by dropping from trees into water and swimming from danger. Their most unusual characteristic is the large size of social groups, often exceeding 100 animals. Although a group contains many adults of both genders, they form same gender-subgroups that have little interaction between males and females except during the breeding season.
Mangabeys (Cercocebus ) are omnivores which emphasize frugivory, especially figs. They are relatively large monkeys (body weights up to 10 kg) with longer muzzles than guenons. Social groups include be either one-male or multi-male units.
Macaques (genus Macaca) are relatively generalized, medium-sized omnivorous monkeys closely related to Papio. Scattered from Gibraltar to Japan, Macaca has the widest geographic distribution of any nonhuman primate genus and is the only cercopithecine genus to be found outside of Africa. Macaques live in multi-male multi-female social groups that place great emphasis upon status hierarchies and matrilineages. Generally, a female macaque depends upon the support of her kin, and matrilines must include numerous daughters to retain their political power. If sons leave their natal groups, they presumably do not usually play important roles in matriline politics. While males move from group to group, but females usually are permanent members of their troop. Groups vary greatly in size depending upon the species and local ecology. Males undergo color changes during the mating period; their faces redden, scrotum and ischial callosities brighten. Male-male aggression increases. Females exhibit red faces and show changes in sexual skin. Portions of their forearms and leg skin also can redden and change texture.
The three genera of African baboons (Mandrillus, Papio, and Theropithecus) are not closely related. The term baboon refers to large bodied African cercopithecines who adapted to a terrestrial econiche by emphasizing sexual dimorphism and placing females and young under the defensive protection of muscular males with dagger-like canine teeth. The long face has a dog-like muzzle and buttress-like reinforcements of maxillary bone. Baboons lack enamel on the lingual surfaces of the mandibular incisors. M3 always has a fifth cusp (a hypoconulid). Both genders have very conspicuous ischial callosities that are joined by hairless perianal skin. Genitalia separate the ischial callosities of females whereas male callosities and perianal skin appear as a continuous pad across the rump.
Baboon behavioral biology reflects the need for every female to remain in the protective shadow of one or more adult males when foraging in the savannah away from trees. Baboons are poor climbers with short digits, short tails, and Intermembral Indexes between 95 and 100. Females generally have sexual swellings, inflation and color changes of the labia and perianal tissues during estrus. All baboons are omnivores, but their diet emphasizes roots, tubers, grass seeds and fruits. They are opportunistic hunters, taking almost any animal smaller than themselves, from invertebrates to vervet monkeys.
Since mandrills and drills (Mandrillus) live in dense western African forests where grasses are less common, their diet contains more leaves and fruit. Males are large (+50 kg.) with dark pelage and vividly colored rumps. The colorful mandrill in particular has pigmented face, perianal region, genitalia, and callosities that are combinations of lacquer-red, scarlet, electric cobalt blue, and gradations of purple, violet, and green. Drill males lack bright facial pigments but have lighter chin and throat hair that outline the dark face.
Savannah baboons, Papio, are the most-studied baboon genus. Their commonplace location on the African continent reflects the wide distribution of their preferred woodland savannah habitat. Olive and yellow baboons form multi-male multi-female groups that range in size from 20 to 200 animals. Although they have large home ranges (up to 4,000 ha), they usually forage as a group. Females are the more permanent members of troops, since males may move from troop to troop. Females seldom migrate and female social relationships form a stable basis for troop social interactions. Males compete intensely for dominance status. A large troop may have more than one subset of politically allied males, but a group of cooperating males control the troop and police it to break up fights and to control group activities. Higher ranking baboons often supplant subordinates from localized food sources even when it would require less energy to find one's own feeding spot than to supplant another animal from a location that is partly consumed. Females too have intensive dominance interactions, and are usually subordinate to males because of their smaller body size.
A major function of high ranking males is group defense. If a predator is encountered, the troop flees into nearby trees. If that is not possible, one or more males defends females and young. At night, all sleep in trees for security. If trees are not available, baboons crowd onto a rocky cliff, or some other relatively inaccessible location. Without the security of trees, females and young need the security of close proximity to one or more fully adult males.
Much of the savannah habitat is subject to great seasonal fluctuations in rainfall. In the dry season large numbers of baboons may congregate near their few permanent water sources. In wetter seasons, troops may break up into smaller units. Guinea and chacma baboons have been described as seasonally subdividing into smaller groups for independent foraging. Females must always be accompanied by adult males if they are to be secure from predation, and there is a tendency for females to follow the same subsets of males on successive years. Indeed, some Chacma troops are seasonal one-male units.
Hamadryas baboons, found in the highlands of Ethiopia, have taken this trend to an extreme. Troops are multi-male and multi-female, but females are bonded to particular males. They spend their time in contact or only a few feet from this male. If a female moves too far away from the male to which she is bonded, he threatens her with aggression. Hamadryas troops consist of male kin who support each other and who respect and defend harems of their kinsmen. A troop fragments into harem units for foraging and congregates before approaching the sleeping cliffs for the night. If a harem unit encounters males from another troop during the day, the latter may attempt to steal females. Such females immediately bond to their new harem males. In this way, females passing from group to group become an important mechanism for gene flow between troops. Hamadryas females are likely to be separated from their offspring. Daughters do not remain in their father's harem. As they reach adolescence, another troop male bonds them to him.
Hamadryas social behavior is a logical extension of the basic pattern of a baboon's emphasis upon male protection. What more fail-proof way of keeping each female and her young in the protective presence of an adult male than by bonding small sets of adults together and providing behaviors (herding) that insure their proximity?
The ecology of gelada baboons, Theropithecus,
of the high Amhara plateau of Ethiopia, is similar to that of
hamadryas baboons. There are also parallels in social behavior.
Geladas are physically distinct and are not closely related to
the other baboon genera. Chests of both gelada genders exhibit
distinctive red hourglass patches of naked skin. Females have
rows of caruncles outlining these patches that extend down their
thighs and enlarge during estrus. They find refuge and safety
on steep cliffs and canyons where they congregate in large unstable
groups that scientists have labeled as "herds" or "bands."
Herds as large as 600 animals are reported, but these are surely
aggregates of smaller bands. Within the herd, geladas are organized
into harems, similar to those of hamadryas baboons, and groups
of bachelor males. As in hamadryas, females are bonded to a male
who plays a role of "herder" and defender. The actual
herding, however is based on a different emotional biology. Male
geladas herd with submissive gestures, and if a female gets into
trouble, instead of the male neck-biting the female, the gelada
female attacks and punishes the male. Thus the same social adaptation
in gelada and hamadryas is reached through very different underlying
emotional mechanisms. Males of both species perform a very programmed,
stereotyped role of herding (return
to outline).
The Colobinae are a group of Old World monkeys with a specialized folivorous diet. Their sacculated stomachs and gut microorganisms enable them to digest cellulose. Fermentation occurs in the fore-stomach and gases of fermentation (methane and carbon dioxide) are expelled by belching. Only the distal compartment contains acid and digestive enzymes. Colobines are relatively arboreal and lack the characteristic cercopithecine cheek pouches. Their skulls are distinguishable from those of other cercopithecoids by their greater interorbital width. Colobinae often exhibit an unusual pattern of infant rearing in which infants are passed from mother to mother, maturing in a troop composed of mothers and mother surrogates. Social organization varies among various species from monogamous family groups or small groups of a single adult male and one or two females and young, to multi-male, multi-female groups.
The African colobines (Colobus, Procolobus, and Piliocolobus) are acrobatic, swinging and jumping with elongated hook-like hands. The name Colobus is from the Greek "kolobos" which means mutilated, a reference to the very small or absent thumbs found in Colobinae. Asian leaf monkeys (Presbytis, Pygathrix, Nasalis, Simias, and Rhinopithecus) are very diverse and are the most common forest mammals in some areas. Larger bodied species are dimorphic. They occupy almost every ecological zone from dry forests of India to mangrove swamps; coastal forests to snow-covered high altitude mountain forests.
Many leaf monkeys are relatively
terrestrial. The Hanuman langur, for example, may spend 80% of
its day on the ground. This large (up to 20 kg) langur, the sacred
langur of India, is named after Hanuman, a Hindu monkey god. This
was the first monkey species that was discovered to exist in two
contrasting social systems. In some ecological circumstance they
form large multi-male multi-female groups; in other localities
they exhibit one-male troops. It was in Hanuman langur one-male
groups in which infanticide was first observed to accompany changes
in male tenure. Attacks on one-male troops by all-male groups
sometimes resulted in killing or driving away the resident male.
Resident male juveniles would also be killed or driven away. The
new males fought among themselves until only one remained. The
surviving male then killed any surviving infants without regard
to the infant's gender. Surprisingly, female protection of the
infants seemed suspended during infanticide associated with establishment
of new males.
Humans and their close relatives, the apes, comprise the hominoids. Extant hominoids are characterized by the absence of tails and rather primitive rounded molar teeth. Lower molars have expanded talonids and five cusps, an arrangement called the Y-5 pattern of molar cusps. Upper molars are quadrate and less specialized than the bilophodont molars of the cercopithecoids.
The lower trunk is characterized
by a broad ilium and broad femoral condyles. Hominoids share characters
of the upper limb and trunk that permit brachiation:
long arms
long curved fingers with powerful flexor tendons
a fibrous meniscus separates the ulna from carpal bones
short olecranon process on ulna
very stable elbow joint
dorsally positioned shoulder
relatively spherical humerus head
wide range of motion of shoulder
long and robust clavicle
stable clavicular-sternal articulation
ossified broad sternum
broad thorax
short and stable lumbar region
no tail (return to outline)
The gibbon (Hylobates) and siamang (Symphalangus) are the smallest and most numerous of the apes. Gibbons are smaller (about 6 kg) than siamangs (about 10 kg). Hylobatids are sometimes referred to as the lesser apes, a reference to their relatively small body size. Both genera exhibit very little sexual dimorphism and have very primitive molar teeth. Relative to body size, the arms are particularly long, and they are the best of primates at brachiation. They have the longest forelimbs relative to body size of all primates, an Intermembral Index range of about 130 to 140. Like cercopithecoids, they have ischial callosities.
They are the only hominoid that does
not build sleeping nests. Although omnivorous, their diet consists
primarily of fruit, and territories are positioned to control
or have access to important fruit trees. Their arm-swinging type
of locomotion allows them to feed at the very end of springy tree
branches. Groups, usually monogamous pairs and their young, occupy
small, intensely defended territories. Siamangs have a naked air
sac on the throat that serves as a sound resonating chamber. Both
siamang and gibbon adults attract attention to themselves with
loud duets of calling, and the morning forest reverberates with
their songs (return to outline).
The great apes are large-bodied, forest primates that build nests in trees and spend a great amount of time on the ground. Although they have the anatomy of brachiators, unlike the gibbon that walks upright when it does come to the ground, great apes are habitually quadrupedal. Although the long fingers of ape hands are flexed for quadrupedal walking, the orangutan (Pongo) balls the hand into a fist while the chimpanzee (Pan) and gorilla (Gorilla) support their weight on the dorsal surfaces of the flexed fingers, a behavior called knuckle-walking. Orangutans and gorillas are very dimorphic with the female only attaining half the body weight of an adult male:
| species | sex | approximate body weight |
| orangutan | m | 80 kg |
| orangutan | f | 40 kg |
| gorilla | m | 160 kb |
| gorilla | f | 80 kg |
| chimpanzee | m | 40 kg |
| chimpanzee | f | 30 kg |
Pongo
Orangutans, found today only on the islands of Borneo and Sumatra, are survivors of an earlier clade than the one represented by humans and African apes. Orangutan teeth have particularly thick enamel with wrinkled occlusal surfaces. Although normally quadrupedal when on the ground, their locomotor anatomy is specialized for slow, suspensory, quadrumanous climbing. Orangutan diet emphasizes soft fruits, seeds and new leaves. Their dependence on soft fruits present a problem for conservationists since the tree species that produce the preferred fruits are found on soils which have agricultural potential, thus placing orangs in direct competition with human agriculturists.
Orangutans have a noyau social organization.
Females and their young occupy small home ranges (70 ha) and move
relatively short distances during foraging. Adult males establish
ranges that overlap those of several females and patrol their
territories to prevent other males from encroaching. Young males
or nonresident males are thought to range widely and may attempt
to capture and forcibly mate with adult females (return to outline).
Pan
Chimpanzees are omnivorous, supplementing fruits with insects and small animals. They form multi-male, multi-female troops of 30 to 80 animals and exhibit very strong dominance hierarchies, males generally being dominant to females. Social behaviors of the pygmy chimpanzees, misnamed since they are not smaller than common chimpanzees, are unusual in their strong mother-son bond. Like other chimpanzees they form multi-male, multi-female troops. Females and immature animals transfer between groups with relative ease. Adult males do not. Young females leave their natal troops and may move again with their immature offspring. Mothers form strong bonds with their sons, and females with adult sons form the high ranking, stable nucleus of pygmy chimpanzee troops.
A basic pattern in chimpanzee ecology is dispersal of group members throughout the core area in search of food resources, communication of discoveries, and sharing of food resources. A tree in fruit becomes a magnet to which calls and activities draw other group members who share the discovery. Chimpanzees also cooperate to hunt and kill other mammals, the most common being colobus monkeys.
Chimps use tools in a variety of
ways. They make leaf sponges to get rain water from a tree bowl
or to clean their bodies. They readily modify sticks or plant
stems and use them to retrieve objects (such as termites) from
inaccessible places. Termiting is a popular activity in some areas.
Several sticks or twigs are stripped of all side branches or leaves.
Tools in hand, a chimp searches for an appropriate termite nest.
When the stick is inserted into a termite mound, some of the termites
are eaten from those clinging to the withdrawn stick. Goodall
(1986) reports that termite "fishing" comprises at least
80% of the total time spent feeding on insects (return to outline).
Gorilla
Gorillas are primarily terrestrial, even building sleeping nests on the ground. The mountain gorilla, estimated to number less than 400 animals and threatened with extinction from human pressures, is the source of most of our knowledge about Gorilla in natural habitats. Gorillas, with greatly enlarged digestive tracts, specialize in eating leaves, wood pith, bamboo, stems, vines, and other vegetable materials. The western gorilla is thought to be more frugivorous. A fully grown male gorilla has a saddle of gray or white hair on the back (silver back), making him easy to distinguish from younger black backed subadult males.
Gorillas live in cohesive bisexual groups of 5 to 40 animals. All bisexual groups have at least one silver backed male, and the most frequently seen group composition is a single dominant silver back male who serves as leader, several females and young, and one or more black backed males. Both genders leave their natal groups, and although some silver backs attempt to keep certain females with them, adult females can transfer between bisexual groups. Sometimes daughters remain with their mothers or later transfer to the same bisexual troop that their mothers have joined.
Though intragroup aggression is relatively
infrequent, adult males are very aggressive toward nongroup males.
Most subadult males are solitary, waiting an opportunity to establish
themselves with females from nearby troops. Gorillas have very
small day ranges, sometimes less than 0.5 km and core areas often
overlap between bisexual groups. If a distant contact with a dangerous
human is detected, the group simply melts quietly into the vegetation.
If the intruder is close enough to be an immediate threat, the
adult male will attack without hesitation. In intermediate situations,
silver back males display fiercely, giving their group opportunity
to escape. The display includes vocalizations, one or more charges
that begin bipedally and continue quadrupedally toward the intruder.
If the intruder remains immobile, neither advancing or retreating,
the silver back display may end with loud thumps on the ground
as he terminates the encounter and follows his group to safety
(return to outline).
Homo
The most obvious human (Homo) characteristic, obligatory bipedal locomotion, is produced by a constellation of functionally related characters:
shortened toes and reduced opposability of the toes
enlarged first toe that propels the body during striding
elongated tarsal and metatarsal segments of the foot
foot has well developed arches
long, powerful legs
knees lock in full extension
knees are positioned toward the body's center of gravity
short, robust coxa
s-shaped spinal column
Another unique human character is our ability to shed body heat through the skin, a feature that involves a reduction in body hair. Dentally, humans have reduced canines to the extent that the canine/pm3 honing mechanism is lost. The robusticity of the face, especially the mesial part of the face is quite reduced. The symphysis of the mandible is reinforced with an external bar of bone, a chin. Hands have shortened fingers and a relatively long opposable thumb. These characters are reflected in changes in motor cortex that supports skill to hands for manipulation and to ankles for walking. The human mean brain volume of 1345 mm3 is more than twice that of any other primate species, and humans are unusual in the high skills they exhibit in technology, culture and language.
Most human societies practice polygyny,
but there is great individual and societal variation in grouping,
mating, and bonding patterns. The unique feature of human society
is the ability to extend the group's social organization and membership,
through the use of language, to very large groups (return to outline).
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