TELLING THE PRIMATES APART

There are lots and lots of living primates: perhaps as many as 250-300 separate species. Primatologists group them into two basic kinds: Prosimians and Anthropoids.

How Do You Tell A Prosimian From An Anthropoid? It’s easy, just look at their faces, teeth and skulls. Prosimianshave

  • wet noses (anthropoids have dry noses)
  • long snouts (anthropoids have short faces)
  • tactile vibrissa (anthropoids don’t have these)
  • a dental comb (i.e., their lower incisors and canines aren’t vertical, like those of the anthropoids, but are horizontal and use as a comb for their fur)
  • immobile faces (anthropoids have mobile faces – cause they depend on their facial expressions to communicate lots of messages)
  • mobile ears (anthropoids have immobile ears)
  • depend a lot on their sense of smell (anthropoids have a poor sense of smell)
  • and their eyes aren’t completely forward-facing (anthropoids eyes are fully forward), but prosimians have really great 3-D vision, like all primates. Just recall how the sifakas can jump 20 or more feet horizontally and land on thorny tree trunks without stabbing their hands or feet).

And if you had some skulls to examine you’d see that

  • although prosimians and anthropoids have a bony ring completely encircling each eye, prosimians lack the post-orbital septum of anthropoids
  • the lower jaw of prosimians consists of two bones (the anthropoids lower jaw consists of a single bone

Prosimian / Anthropoid

Ring-tail lemur face /
Ring-tail lemur skull /
Spider monkey face /
Spider monkey skull

The Anthropoids Are Divided Into Two Basic Kinds: Platyrrhines (the American monkeys) and Catarrhines (monkeys and apes of Africa and Asia, plus all humans). How do you tell the former from the latter. It’s easy, look at their faces, do a quick dental exam and then look at their rear end. Platyrrhines:

  • have nostrils that are far apart and open to the sides (catarrhines have nostrils that are closely spaced and open downward or directly forward)
  • are, on average, smaller than catarrhines
  • have an extra premolar which gives them a total of 36 teeth in adults (catarrhines have a total of 32 teeth)
  • have prehensile tails – at least most do (catarrhines do NOT have grasping tails, and some catarrhines, such as the apes, have NO tails)
  • live only in the trees in forests (catarrhines can be found in a wide variety of niches and habitats)
  • LACKischial callosities (thick pads of calloused skin found on the butts of many cattarhine monkey species)

Platyrrhine / Catarrhine
Uakari face:
notice nostrils / Prehensile tail / Orangutan Face:
notice nostrils / Hanuman langur:
no prehensile tail
No ischial callosities /
Crested black macaques:
Ischial callosities /
Macaques:
Ischial callosities

The Catarrhines Are Divided Into Two Basic Kinds: Monkeys of Africa and Asia and the Hominioids (apes and humans). How do you tell the former from the latter? All monkeys have:

  • tails (no hominoids have tails)
  • a lengthened lower spine, which gives the lower back great flexibility (hominoids have a compressed lower spine)
  • chests that are narrow side to side, but deep front to back (hominoids have wide chests that are shallow front to back)
  • shoulder blades – called scapula – that lie along the sides of the rib cage (hominoids have scapula that like on the back of the rib cage)
  • wrists with limited side to side movement (hominoids have a much greater side-to-side range of motion in their wrists)
  • elbows that prevent complete extension of the arm (hominoids can completely extend their arms)
  • molars with very high crowns and inter-connected cusps (hominoids have low crowns and very simple, rounded cusps)
  • a narrow pelvis (hominoids have a broad pelvis)
  • a shoulder that prevents brachiation (hominoids are excellent brachiators, you know, they can suspend themselves beneath branches and then swing from branch to branch)

The Catarrhine monkeys are divided into two basic kinds: leaf-eaters (which includes the langurs) and cheek-pouched. How do they differ? Primarily in their dietary adaptations.

  • The cheek pouch monkeys feed on an array of fruits, seeds, nuts, flowers, buds, leaves, grass and animal prey. Cheek pouch monkeys get their name from pouches formed by the superficial facial muscles which stretch into pockets inside the mouth. As an individual forages, the fruits, seeds, or leaves are stuffed into each pouch. This method of collection allows the animal to store food temporarily and permits it to eat and run.
  • The leaf eating monkeys, as their name implies, rely mainly on more difficult to digest and lower caloric value foods such as leaves and other foliage, lichens, and unripe fruit. The leaf-eating monkeys also have enlarged, chambered sacculated stomachs that resemble those of cows and other ruminants, and a large intestinal tract for storing bulky foliage.

The hominoids are divided into several basic kinds: the small-bodied apes (gibbons and siamangs), the large-bodied apes (chimpanzees, bonobos, gorillas, orangutans) and the hominids. How does one tell them apart?

Small-bodied apes (Gibbons and siamangs)

  • Gibbons and siamangs live in Southeast Asia, are almost entirely fruit-eaters, they are the best brachiators of all the primates (yes, even better than the American spider monkeys), they are highly arboreal and rarely come to the ground, but when they do they walk bipedally; they also walk bipedally in the trees, grasping branches with their feet and holding their long arms out for balance, like tight-rope walkers. They have very long arms, hands and fingers. The relatively short thumb is set well down on the palm, and their fingers form a hook, which is used during brachiation.

Large-bodied apes (Orangutans, Gorillas, Chimpanzees, Bonobos)

  • Orangutans (today) are found only in the rainforests of Borneo and northwestern Sumatra. Males are over twice the size of females (a trait know as sexual dimorphism). Orangs are primarily fruigivores and they move through the forest canopy searching for fruit. They have long arms, short legs, and large grasping feet that are nearly indistinguishable from their hands. Orangs rarely feed and associate together (due to the infrequent distribution of fruit). In Sumatra, orangs make and use tools to acquire social insects and fruits with hard shells (this behavior is learned through observation and experimentation).
  • Gorillas come in two species: lowland gorillas and mountain gorillas. Unlike orangutans and gibbons, gorillas travel, feed and sleep on the ground. Sexual dimorphism is marked among gorillas. Although gorillas eat fruit when available, it makes up less than 15% of their diet. Most of their food comes from leaves, pith and bark. Some gorillas also eat insects. Social groups include adult females, young of several ages, black-back teenage males, and at least one fully mature alpha male (called a silverback).
  • Chimpanzees are widely distributed throughout the rain forests of central Africa, from Lake Tanganyika into western Africa. They are our closest living relatives and we look to them for clues about the origin of human anatomy and behavior, especially cultural behavior. Chimps routinely form hunting parties to hunt monkeys, and the composition and hunting style varies depending on the particular environment and chimpanzeee group. Chimps also make and use tools (most frequent makers and users are females), alter the symbolic meaning of vocalizations, and some chimps may even use certain plants to treat intestinal parasites. Chimpanzees live in communities of about 50 mixed females and males who share a common home range, and in which smaller subgroups associate, come together and separate according to social and ecological circumstances (a pattern known as fission-fusion). Chimpanzees establish territorial boundaries that are frequently patrolled by males. And if they encounter individuals from other communities, they may display aggressively or attack those individuals.
  • Bonobos, or gracile chimpanzees, are found only in the large central river basin of the Congo River. They are similar in many ways to chimpanzees, but differ in details of anatomy and behavior, especially their sexual behavior. Bonobos have smaller canine teeth, narrower and slighter chests, shorter forelimbs, and longer hind limbs. They have a propensity to stand and walk on two legs much more frequently than any other primate species, save hominids. Like chimpanzees, bonobos make and use tools.

Bonobo social interactions differ markedly from those of chimpanzees and adult social relationships are more affiliative and tolerant than among chimps. With the exception of humans (and some orangutan females), bonobos are the only primate species to engage in sexual activity for purposes other than procreation. In fact, bonobos engage in many forms of sexual activity for purposes similar to purposes that motivate humans: affection, boredom, forming bonds, gaining favors, etc. Sexual activity is frequent between females as well as between males and females.

Bonds among female bonobos are very stong. When an adolescent female enters a new community, she forms a bond with an older female, which helps her integrate into the group where she spend the rest of her life. The bonding is initiated by the newcomer rubbing her genitals against those of a high-ranking female who then acts as her sponsor, introducing her to the alpha female of the group, with whom the newcomer also rubs genitals. Grooming and sharing are frequent among adult females. Females eat meat and hunt. Female-male bonds are strong; they are frequent grooming partners, and males often share food with females.

Hominids (all species, living and extinct)

  • Physically, hominids are distinguished from all other hominoids by a suite of anatomical changes to their skeletons. These changes are related to the hominids mode of locomotion, habitual upright bipedalism. The most important of those changes are:
  • The foramen magnum (the hole in the skull through which passes the spinal cord) is located directly under the braincase (in the other hominoids it is located rearward)
  • An S-shaped spinal column (in the other hominoids it is one long curve)
  • A bowl-shaped pelvis (in the other hominoids it is flat)
  • The upper legs angle in – thus we are knock-kneed (in the other hominoids the legs are parallel)
  • The big toe is in line with all the other toes and is not opposable (in the other hominoids the big toe diverges from the other toes and can be opposed to them)
  • The foot has two fixed arches, one front to back and one side to side (in the other hominoids the foot is prehensile)

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