Primate Development and Taxonomy

Origins

The major evolutionary trends that distinguish primates and their generalized mammalian form came as a result of adaptation to arboreal living.

Other placental mammals tended to adapt to grasslands, marine or other environments, but the adaptive niche for primates was the trees
--provided many challenges and opportunities
 


This is called the arboreal hypothesis and has been criticized by Matt Cartmill. He proposes a visual predation hypothesis
--suggests the first adaptation was to the lower tier of the forest canopy and the brush, as "stealthy" eaters of insects
--they need foward-facing eyes and partially grasping hands to do so

Visual predation and the arboreal hypothesis are not mutually exclusive explanations, with the visual predation traits elaborated as the primates moved to the trees. Whatever the case, we know they eventually moved to the trees.

 

Classification

In the Linnean taxonomic system, we start with the highest level, the order Primates, with the next level down divided into two large categories: Prosimii (lemurs, lorises, and usually the tarsiers) and Anthropodiea (monkeys, apes and humans). At successively lower levels (infraorder, superfamily, family, genus, and species) --see the text, page 218, figure 9.7 for a detailed chart, but this chart gives a more general view:

 

primate taxonomy

Primate taxonomy based on morphology has critiques.
For example: some say that tarsiers have both prosimian and anthropoid traits and are biochemically closer to anthropoids. Hominoids have traditionally included four species in one family (the Pogidae-gorillas, chimpanzees, bonobos, and orangutans), as separate from humans (Hominidae) but seem actually to have both Asian and African branches. DNA studies have complicated it further, indicating the closeness of humans and chimpanzees, with gorillas further away. Some have even suggested that chimps be labelled Homo troglodytes. The point is that the taxonomic system is in flux as new data are utilized. Most experts still use the traditional system.

 

Prosimians

The most primitive of the true primates: lemurs and lorises
 

Lemurs:
Found only on the Island of Madagascar and adjacent island off east Africa, thye are extremely diversified into a range of niches-22 surviving species
Size range from the mouse lemur with head and trunk length of only five inches to the indri a bit over two feet long.
Larger lemurs are diurnal and eat a variety of leaves, fruits, buds, bark and shoots; smaller are nocturnal and insectivorous
Considerable variation in behavior. Some are arboreal while others are terrestrial. Socially several species live in groups of 10-20 animals. Some like the indri live in monogamous family units. Some nocturnal forms are solitary.

Lorises
Similar in appearance to lemurs, but survived in contental areas of India, Sri Lanka, Southeast Asia, and Africa.
Five species, largely nocturnal. Galagos are included as well, with 6-9 additonal sepcies. They are slow, cautious, quadrupedal climbers who can suspend themselves on hind limbs leaving hands for feeding. Some are entirley insect eaters while others supplement the diet with leaves, fruits, and slugs. Food foraging is often solitary.

Lemurs and lorises are at the same adaptive level. Good grasping and climbing abilities and well-developed visual ability, though stereoscopic ability not as developed as it is in anthropoids. Most have a claw-grooming claw on second toe. Life span is about 14 years for loris and 19 years or lemurs.

Tarsiers
Three species restricted to island areas in SE Asia. They live in a wide range of habitats. They are nocturnal insectivores, and leap onto prey from branches and shrubs. They form pair bonds, with the social unit being the mated pair and offspring.
Unlike loris and lemurs, they have no rhinarium and they have a eye sockets enclosed by bone t back and sides. This is more like an anthropoid. Eyes are enormous, compared to the rest of the body.
They have taxonomically mixed traits.

Anthropoids

The traits that distinguish anthropoids from prosimians include:

The monkeys represent 70% (about 130 species) of all primates and are the most varied. New species are still being discovered and there are debates about taxonomy.

Two main groups, New and Old World monkeys, have several million years of distinct evolutionary history. They had a strikingly parallel evolution with similar selective pressures in tropical arboreal environments
Some say they evolved independently while others claim a common ancestor sometime before 50 million years ago.

New World Monkeys
A wide range of size, diet and ecological adaptation. Marmosets and tamarins weigh about 12 ounces at the small end, and howlers weigh up to 20 or so pounds.
Almost exclusively arboreal, some never coming to the ground
All but one species in diurnal, living in most forested areas of southern Mexico into Central and South America.

Major characteristic is the shape of the nose. New World have broad, widely flaring noses with outward-facing nostrils-
sometimes called platyrrhine or flat-nosed

Two families: Callitrichidae and Cebidae Callitrichidae are the most primitive monkeys: marmosets and tamarins as examples

Cebids--at least 30 species ranging from foot-long squirrel monkey to the howler (2 ft.).
 

Old World Monkeys
Much more variety in morphology and behavior than New World monkeys
They have downward facing noses and are called catarrhine.

The most widely distributed of non-human primates, ranging from tropical forests to semi-arid deserts and seasonal snow-covered areas in northrn Japan.
Most are quadrupedal and primarily arboreal, but some (like baboons) are well adapted to the ground
Most hold their upper bodies erect for long periods of time while feeding, sleeping, and grooming-associated with it is hard skin on the buttocks called ischial callosities-serve as sitting pads
Most have a great deal of manual dexterity
Most have tails that are used in both balance and communication.

Only one recognized family: Cercopithecidae
Two subfamilies: cercopithecines and colobines

Locomoton varies from arboreal to terrestrial quadrupedalism to semibrachiation to acrobatic leaping.
Sexual dimorphism is typical of land species like baboons, with male weight (80 lbs.) often twice that of females

Females often exhibit pronounced cyclical changes of the external genitalia with swelling and redness during estrus, a hormonally initiated period of sexual receptivity correlated with ovulation.

Several types of social groups:
Colobines tend to live in small gropups with only one or two adult males, whereas cercopithecines live in large groups with several adults of both sexes and offspring of all ages.

Hominoids

Superfamily Hominoidea includes the "lesser" apes placed in the family Hylobatidae: gibbons and siamangs
Also includes the great apes in the family Pongidae: orangutans, gorillas, chimpanzees and bonobos.
Hominidae: humans

Apes and humans differ from monkeys in many ways including:
 

Gibbons and Siamangs
Eight gibbon species are found in tropical areas of SE Asia. Small, weighing 13 pounds for gibbon and 25 for saimang. Extremely good brachiators due to very long arms, permanently curved fingers and powerful shoulders. Mostly a fuit diet, supplemented by leaves, insects. Social unit is monogamous pair and offspring. Both males and females are highly territorial.

Orangutans
Represented by two subspecies in heavily forested areas of Indonesian islands of Borneo and Sumatra. they face extinction due to poaching and diminution of their habitat. The are slow, cautious climbers who use all four limbs for locomotion. Almost completely arboreal, but do travel quadrupedally on ground for short distances. Very large animal that may weigh 200 lbs. for males, 100 for females. They are frugivorous, but supplement with leaves, insects and some meat.

Gorillas
The largest of all living primates, now confined largely to forested regions of central Africa. Two varieties: lowland and highland. They exhibit marked sexual dimorphism with males up to 400 pounds and females at 200 pounds. Weight makes them primarily terrestrial, and semi-quadrupedal knuckle walkers. Family groups consist of one or more large silverback (due to white hair patch across back) males, a few females and subadult offspring. They are not the King Kong stereotype, but are gentle, shy vegetarians. Males will display when provoked, and may attack to defend their group. Probably only 40,000 lowland and 620 highland left due to poaching and habitat problems.

Chimps
Best known of the non-human primates. Structurally similar to gorillas, but ecological adaptations differ. They are mostly terrestrial knuckle walkers, but also can brachiate in trees. May walk bipedally for sort distances. Chimps are highly excitable, active and noisy. Males are about 100 pounds and females around 80. They tend to live in flexible communities of as many as 50 individuals. They are very territorial. They are omnivouous, and even hunt communally to kill small mammals and even other chimps.

Bonobos
Found only in limited area of Zaire River, they weren't recognized as separate from chimps until the 1920s. Least studied of the great apes. They are "pygmy" chimps due to small size, but some claim this is not warranted in that size can be as large as most chimps. They have a more linear build. They are more arboreal than chimps, but less excitable and aggressive. Little physical violence. We know little about them though recent work by de Waal is intriguing.

Genetics

Karyotyping of apes has not demonstrated the evolutionary sequence, but suggests that humans and chimps share a more recent ancestry after splitting from gorillas. More controlled study may clarify.