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5.3: Primate Diversity

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    As we begin exploring the different taxa of primates, it is important to keep in mind the hierarchical nature of taxonomic classification (discussed in Chapter 2) and how this relates to the key characteristics that will be covered. Figure 5.11 summarizes the major taxonomic groups of primates. If you locate humans on the chart, you can trace our classification and see all of the categories getting more and more inclusive as you work your way up to the Order Primates. What this means is that humans will have the key traits of each of those groups. It is a good idea to refer to the figure to orient yourself as we discuss each taxon.

    5.3.1.jpgFigure \(\PageIndex{1}\): This taxonomy chart shows the major groups of primate taxa. Be sure to refer back to this chart as you read through the primate groups so that you can see how each group is related to one another.

    Ways of Organizing Taxa

    Our goal in taxonomic classification is to place taxa into categories that reflect their clade relationships. A clade is a grouping of organisms that reflect a branch of the evolutionary tree, a grouping based on relatedness. Clade relationships are determined using derived traits shared by groups of taxa as well as genetic similarities. An example of a clade would be a grouping that includes humans, chimpanzees, bonobos, and gorillas. These taxa are in what is referred to as the African clade of hominoids. The African clade grouping reflects the fact that humans, chimpanzees, bonobos, and gorillas all share a more recent ancestor with each other than any of them do with other species—that is, we are on the same branch of the evolutionary tree.We know members of the African clade are most closely related based on derived morphological traits as well as genetic similarities. In this grouping, we exclude the orangutan, which is considered a member of the Asian clade of hominoids.

    5.3.2.jpgFigure \(\PageIndex{2}\): Grades vs. Clades: Grouping orangutans, gorillas, chimpanzees and bonobos but excluding humans is a grade classification based on overall similarity in appearance and lifestyle among the apes. We are most interested in groupings based on evolutionary relationships, so we use the clade classification in which humans are grouped with gorillas, chimpanzees, and bonobos. This grouping reflects our evolutionary relationships.

    In contrast, grades are groupings that reflect levels of adaptation or overall similarity and not necessarily actual evolutionary relationships. An example of a grade would be placing orangutans, gorillas, bonobos, and chimpanzees into a group, and excluding humans. Grouping in this way is based on the superficial similarities of the apes in being large-bodied, having lots of body hair, living in tropical forests, using trees, and so on. According to these criteria, humans seem to be the unusual ones in that we differ in our morphology, behavior, and ecology. Separating humans from the other large-bodied apes is the system that was used historically. We now know that grouping orangutans, gorillas, bonobos, and chimpanzees and excluding humans does not accurately reflect our true evolutionary relationships (Figure 5.12), and because our goal in taxonomic classification is to organize animals to reflect their evolutionary relationships, we prefer to use clade classifications.

    Suborder Strepsirrhini

    5.3.3.jpgFigure \(\PageIndex{3}\): The foot of a ring-tailed lemur showing its grooming claw on the second digit.

    The Order Primates is subdivided into Suborder Strepsirrhini and Suborder Haplorrhini, which, according to molecular estimates, split about 70–80 million years ago (Pozzi et al. 2014). The strepsirrhines include the groups commonly called lemurs, lorises, and galagos (Figure 5.14). Strepsirrhines differ from haplorrhines in many ways, most of which involve retaining primitive traits from the last common ancestor of primates. All of the traits discussed below are primitive traits, but strepsirrhines do have two key derived traits that evolved after they diverged from the haplorrhines. The two derived traits are the grooming claw (Figure 5.13), which is on the second digit of each foot, and the tooth comb (or dental comb), located on the lower, front teeth (Figure 5.15). In most strepsirrhines, there are six teeth in the toothcomb—the four incisors and the two canines. Other than the tooth comb, the teeth of strepsirrhines are fairly simple in not being particularly large or distinctive relative to haplorrhines.

    5.3.4.jpgFigure \(\PageIndex{4}\): (Clockwise from top right) sifaka, black-and-white ruffed lemur, loris, galago, slender loris, mouse lemur, aye-aye, and ring-tailed lemur.

    Compared to haplorrhines, strepsirrhines rely more on nonvisual senses. Strepsirrhines have longer snouts than haplorrhines and get their name because they all have wet noses (rhinariums) like cats and dogs. The long snout and rhinarium reflect strepsirrhines’ greater reliance on olfaction relative to haplorrhines. Indeed, many strepsirrhines use scent marking, rubbing scent glands or urine on objects in the environment to communicate with others. Additionally, many strepsirrhines have mobile ears that they use to locate insect prey and predators. As discussed earlier, there are trade-offs in sensory systems, so while strepsirrhines have a better sense of smell than haplorrhines, their visual adaptations are more primitive. Strepsirrhines have less convergent eyes than haplorrhines, and therefore all have postorbital bars whereas haplorrhines have full postorbital closure (Figure 5.1). All strepsirrhines have a tapetum lucidum, a reflective layer at the back of the eye that reflects light and thereby enhances the ability to see in low-light conditions. It is the same layer that causes your dog or cat to have “yellow eye” when you take photos of them with the flash on. It is thought to be primitive among mammals as a whole.

    5.3.5.jpgFigure \(\PageIndex{5}\): The lower front teeth of a ring-tailed lemur showing a tooth comb. Note that there are six teeth in the tooth comb, four incisors and two canines. The teeth that superficially look like canines are actually premolars.

    Strepsirrhines also differ from haplorrhines in some aspects of their ecology and behavior. The majority of strepsirrhines are solitary, traveling alone to search for food, although some taxa are more social. Most strepsirrhines are also nocturnal and arboreal. Strepsirrhines are, on average, smaller than haplorrhines, and so many more of them have a diet consisting of insects and fruit, with few taxa eating primarily leaves. Lastly, most strepsirrhines are good at leaping, with several taxa specialized for vertical clinging and leaping. In fact, among primates, all but one of the vertical clinger leapers are in the Suborder Strepsirrhini.

    5.3.6.pngFigure \(\PageIndex{6}\): Geographic distribution of living strepsirrhines. Lemurs live only on the island of Madagascar, while their relatives the lorises and galagos live across Central Africa and South and Southeast Asia.

    Strepsirrhines can be found all across the Old World: in Asia, Africa, and on the island of Madagascar (Figure 5.16). The Suborder Strepsirrhini is divided into two groups: (1) the lemurs of Madagascar and (2) the lorises, pottos, and galagos of Africa and Asia. By molecular estimates, these two groups split about 65 million years ago (Pozzi et al. 2014).

    Lemurs of Madagascar

    Madagascar is an island off the east coast of Africa, and it is roughly the size of California, Oregon, and Washington combined. It has been separated from Africa for about 130 million years and from India for about 85 million years, which means it was already an island when strepsirrhines got there approximately 60–70 million years ago. Only a few mammal species ever reached Madagascar, and so when lemurs arrived they were able to flourish into a variety of forms.

    5.3.7.jpgFigure \(\PageIndex{7}\): Indris, the largest of the lemurs. These folivorous lemurs are vertical clingers and leapers and live in pairs.

    The lemurs of Madagascar are much more diverse compared to their mainland counterparts, the lorises and galagos. Malagasy strepsirrhines display a variety of activity patterns. While many species are nocturnal, plenty of others are diurnal or cathemeral. They range in body size from the smallest of all primates, the mouse lemur, some species of which weigh a little over an ounce (Figure 5.14), up to the largest of all strepsirrhines, the indri, which weighs up to about 20 pounds (Figure 5.17). Lemurs include species that are insectivorous, frugivorous, and folivorous. A couple of members of this group have specialized in more unusual diets for primates. These include the gummivorous fork-marked lemurs as well as bamboo lemurs, who are able to metabolize the cyanide in bamboo. The most unusual lemur is the aye-aye, which you can see depicted in Figure 5.14. This nocturnal lemur exhibits traits not seen in any other primate, including having rodent-like front teeth that grow continuously and a long-bony middle finger that it uses to fish grubs out of wood. It has a very large brain compared to other strepsirrhines, which it fuels with a diet that includes bird’s eggs and other animal matter. Based on genetic estimates and morphological studies, it is believed that aye-ayes were the first lemurs to separate from all of the other strepsirrhines and so have been evolving on their own since around the time strepsirrhines got to Madagascar (Matsui et al. 2009).

    Lemurs are also diverse in terms of behavior. Many Malagasy strepsirrhines are solitary foragers, but some live in pairs, others in small groups, some in larger groups, and some, like the red-ruffed lemur, are now known to live in complex social groups that are unlike what we see in any other primates (Vasey 2006). It is also among the lemurs that we see some of the best vertical clingers and leapers. Many lemurs are quadrupedal, but even the quadrupedal lemurs are quite adept at leaping. Malagasy strepsirrhines also exhibit a few unusual traits. They are highly seasonal breeders, often mating only during a short window, once a year (Wright 1999). Female ring-tailed lemurs, for example, only come into estrus one day a year for a mere six hours. Malagasy strepsirrhines are also unusual in that females are socially dominant. In most primates, males dominate females because they are typically larger and exhibit greater aggression, but in lemur groups, males and females are usually the same size and females have priority access to resources over males.

    Lorises, Pottos, and Galagos of Asia and Africa

    Unlike the lemurs of Madagascar, lorises, pottos, and galagos live in areas where they share their environments with monkeys and apes, who often eat similar foods. Lorises live across South and Southeast Asia, while pottos and galagos live across Central Africa. Because of competition with larger-bodied monkeys and apes, mainland strepsirrhines are more restricted in the niches they can fill in their environments and so are not as diverse as the lemurs of Madagascar.

    5.3.8.jpgFigure \(\PageIndex{8}\): This slow loris, like all others in this taxonomic group, is solitary and nocturnal, with a diet heavy in insects and fruit.

    All strepsirrhines in Africa and Asia are nocturnal and solitary. Their body sizes don’t range as greatly as the lemurs, and neither do their diets. For the most part, the diet of lorises, pottos, and galagos consist of fruits and insects. A couple of species eat more gum, but overall the diet of this group is fairly narrow when compared to the Malagasy lemurs. Lorises and pottos are known for being slow, quadrupedal climbers, moving quietly through the forests to avoid being detected by predators (Figure 5.18). Because they are not fast moving, these strepsirrhines have developed alternative defenses against predators. Lorises, for example, eat a lot of caterpillars, which makes their saliva slightly toxic. Loris mothers will then bathe their young in this toxic saliva, thus making the babies unappealing to predators. In comparison to the slow-moving lorises and pottos, galagos are active quadrupedal runners and leapers that scurry about the forests at night. Galagos make distinctive calls that sound like a baby crying, which has led to their nickname “bushbabies.” Figure 5.19 summarizes the key differences between these two groups of strepsirrhines.

    Table 5.3.1: Strepsirrhini at a glance: This table summarizes the key differences between the two groups of strepsirrhines.
      5.3.9.jpg

    Lemurs

    5.3.10.jpg

    Lorises, Pottos and Galagos

    Geographic range Madagascar South and Southeast Asia and Central Asia
    Activity patterns Diurnal, nocturnal or cathemeral Nocturnal
    Dietary types Insectivore, frugivore or folivore Insectivore, frugivore
    Social groupings Solitary, pairs, or small to large groups Solitary
    Forms of locomotion Vertical clinger leapers, quadrupedal Slow quadrupedal climbers and active quadrupedal runners

    Suborder Haplorrhini

    When the strepsirrhini and haplorrhini split from one another, strepsirrhines retained more primitive traits (those likely present in the last common ancestor), while haplorrhines became quite different, developing many derived traits. Thus, all of the traits discussed below are considered derived traits.

    As mentioned earlier, the visual systems of haplorrhines are more developed than those of strepsirrhines. Many haplorrhines are trichromatic and, with one exception that will be discussed shortly, all have full postorbital closure (Figure 5.1). This increase in bony closure around the eye protects the more convergent eyes that haplorrhines possess. Haplorrhines also evolved to have a fovea, a depression in the retina at the back of the eye containing concentrations of cells that allow us to see things very close up in great detail. The heavier reliance on vision over olfaction is also reflected in the shorter snouts ending with the dry nose (no rhinarium) of haplorrhines. All but two genera of living haplorrhines are active during the day, so this group lacks the tapetum lucidum which is so useful to nocturnal species. On average, haplorrhines also have larger brains relative to their body size when compared with strepsirrhines.

    The Haplorrhini differ from the Strepsirrhini in aspects of ecology and behavior as well. Haplorrhines are generally larger than strepsirrhines, and so we see many more species that are folivorous and frugivorous, and fewer that are insectivorous. This dietary difference is reflected in the teeth of haplorrhines, which are broader with more surface area for chewing. The larger body size of this taxon also influences locomotion. Only one haplorrhine is a vertical clinger and leaper. Most members of this suborder are quadrupedal, with one subgroup specialized for brachiation. A few haplorrhine taxa are monomorphic, meaning males and females are the same size, but many members of this group show moderate to high sexual dimorphism in body size and canine size. Haplorrhines also differ in social behavior. All but two haplorrhines live in groups, which is very different from the primarily solitary strepsirrhines. Differences between the two suborders are summarized in Figure 5.20.

    Table 5.3.2: Suborders at a glance: This table summarizes the key differences between the two primate suborders.
     

    5.3.11.jpg

    Suborder Strepsirrhini

    5.3.12.jpg

    Suborder Haplorrhini

    Sensory adaptations

    Rhinarium

    Longer snout

    Eyes less convergent

    Post-orbital bar

    Tapetum lucidum

    Mobile ears

    No rhinarium

    Short snout

    Eyes more convergent

    Post-orbital plate

    No tapetum lucidum

    Many are trichromatic

    Fovea

    Dietary differences

    Mostly insectivores and frugivores, few folivores

    Few insectivores, mostly frugivores and folivores

    Activity patterns and Ecology

    Mostly nocturnal, few diurnal or cathemeral

    Almost entirely arboreal

    Only two are nocturnal, rest are diurnal

    Many arboreal taxa, also many terrestrial taxa

    Social groupings

    Mostly solitary, some pairs, small to large groups

    Only two are solitary, all others live in pairs, small to very large groups

    Sexual dimorphism

    Minimal to none

    Few taxa have little/none, many taxa show moderate to high dimorphism

    Suborder Haplorrhini is divided into three infraorders: Tarsiiformes, which includes the tarsiers of Asia; Platyrrhini, which includes the New World monkeys of Central and South America; and Catarrhini, a group that includes the Old World monkeys and apes of Asia and Africa, as well as humans. According to molecular estimates, tarsiers split from the other haplorrhines close to 70 million years ago, and platyrrhini split from catarrhini close to 46 million years ago (Pozzi et al. 2014).

    Infraorder Tarsiiformes of Asia

    5.3.13.jpgFigure \(\PageIndex{9}\): Tarsiers are the only living representatives of this Infraorder.
    5.3.14.pngFigure \(\PageIndex{10}\): Tarsiiformes can be found in tropical forests of Southeast Asia.

    Today, the Infraorder Tarsiiformes includes only one genus, Tarsius (Figure 5.21). Tarsiers are small-bodied primates that live in Southeast Asian forests (Figure 5.22) and possess an unusual collection of traits that have led to some debate about their position in the primate taxonomy. They are widely considered members of the haplorrhine group because they share several key derived traits with monkeys, apes, and humans, including dry noses, a fovea, not having a tapetum lucidum, and having eyes that are close together. Tarsiers also have some traits that are more like strepsirrhines and some that are unique. Tarsiers are the only haplorrhine that are specialized vertical clinger leapers, a form of locomotion only otherwise seen in some strepsirrhines. Tarsiers actually get their name because their ankle (tarsal) bones are elongated to provide a lever for vertical clinging and leaping. Tarsiiformes are also small, with most species weighing between 100 and 150 grams. Like strepsirrhines, tarsiers are nocturnal, but because they lack a tapetum lucidum, tarsiers compensate by having enormous eyes. In fact, each eye of a tarsier is larger than its brain. These large eyes allow enough light in for tarsiers to still be able to see well at night without the reflecting layer in their eyes. To protect their large eyes, tarsiers have a partially closed postorbital plate that is somewhat intermediate between the postorbital bar of strepsirrhines and the full postorbital closure of other haplorrhines (Figure 5.23). Tarsiers have different dental formulas on their upper and lower teeth. On the top, the dental formula is 2:1:3:3, but on the bottom it is 1:1:3:3. Other unusual traits of tarsiers include having two grooming claws on each foot and the ability to rotate their heads around 180 degrees, a trait useful in locating insect prey. The tarsier diet is considered faunivorous because it consists entirely of animal matter, making them the only primate not to eat any vegetation. They are also only one of two living haplorrhines to be solitary, the other being the orangutan. Most tarsiers are not sexually dimorphic, like strepsirrhines, although males of a few species are slightly larger than females.

    5.3.15.jpgFigure \(\PageIndex{11}\): Skull of a tarsier showing very large eye sockets and partially closed postorbital plates.

    Two alternative classifications have emerged due to the unusual mix of traits that tarsiers have. Historically, tarsiers were grouped with lemurs, lorises, and galagos into a suborder called Prosimii. This classification was based on tarsiers, lemurs, lorises, and galagos all having grooming claws and similar lifestyles (e.g., small, nocturnal, more leaping locomotion, diet heavy in insects, more solitary). Monkeys, apes, and humans were then separated into a suborder called the Anthropoidea. These suborder groupings were based on grade rather than clade. Today, most people use Suborders Strepsirrhini and Haplorrhini, which are clade groupings based on the derived traits that tarsiers share with monkeys, apes, and humans (e.g., more postorbital closure, fovea, no tapetum lucidum, dry nose). The Strepsirrhini/Haplorrhini dichotomy is also supported by the genetic evidence that indicates tarsiers are more closely related to monkeys, apes, and humans (Jameson et al. 2011). Figure 5.24 summarizes the unusual mix of traits seen in tarsiers.

    Table 5.3.3: Tarsiers at a glance: Tarsiers have a mix of traits that lead to debate about their classification. Some of their traits superficially resemble strepsirrhines, but they share many derived traits with haplorrhines. They also possess unique characteristics that are unlike any other primates.
    Like Strepsirrhini Unique Like Haplorrhini

    Very small

    Nocturnal

    Highly insectivorous

    Solitary

    Vertical clinger-leapers

    Little/no sexual dimorphism

    Two grooming claws

    2:1:3:3/1:1:3:3 dental formula

    Do not eat vegetation

    Can rotate their heads nearly 180 degrees

    Almost full PO closure

    More convergent eyes

    No tapetum lucidum

    No rhinarium

    Genetic evidence

    Fovea

    Infraorder Platyrrhini of Central and South America

    image34-e1565280112241.pngFigure \(\PageIndex{12}\): Geographic distribution of the platyrrhines across Central and South America. New World monkeys are the only naturally occurring non-human primates in the Americas.

    The platyrrhines, also commonly called New World monkeys, are the only non-human primates in Central and South America (Figure 5.25) and so, like the lemurs of Madagascar, have diversified into a variety of forms in the absence of competition. Infraorder Platyrrhini get their name from their distinctive nose shape. “Platy” means flat and “rhini” refers to noses and, indeed, New World monkeys have noses that are flat and wide, with nostrils that are far apart, facing outward, and usually round in shape (Figure 5.26). This nose shape is very different from what we see in catarrhines, the group that includes Old World monkeys, apes, and humans.

    image35-2.jpgFigure \(\PageIndex{13}\): A capuchin monkey demonstrating a typical platyrrhine nose shape with round nostrils pointing outward on a flat nose.

    On average, Platyrrhini are smaller and less sexually dimorphic than catarrhines, and they have retained the more primitive primate dental formula of 2:1:3:3. Platyrrhines are also all highly arboreal, whereas many Old World monkeys and apes spend significant time on the ground. The New World monkeys also differ in having less well-developed vision. This is reflected in the wiring in the visual system of the brain but also in their polymorphic color vision. The genes that enable individuals to distinguish reds and yellows from blues and greens are on the X chromosome. Different genes code for being able to see different wavelengths of light so to distinguish between them you need to be heterozygous for seeing color. In New World monkeys, each X chromosome carries the genes for seeing one wavelength. This means that male platyrrhines (having only one X chromosome) are always dichromatic. Female platyrrhines can be dichromatic (if they are homozygous for the same version of the color vision gene) or trichromatic (if they are heterozygous) (Kawamura et al. 2012). We currently know of two exceptions to this pattern among platyrrhines. Owl monkeys, which are nocturnal, are monochromatic, meaning that they cannot distinguish any colors. The other exception are Howler monkeys, which have evolved to have two color vision genes on each X chromosome. This means that both male and female howler monkeys are able to see reds and yellows. As we will discuss, all Old World monkeys, apes, and humans are trichromatic.

    Platyrrhines include the smallest of the monkeys, the marmosets and tamarins (Figure 5.27). These small monkeys, all of which weigh less than 1 kilogram, live in cooperative family groups, wherein usually only one female reproduces and everyone else helps carry and raise the offspring. They are unusual primates in that they regularly produce twins. The diet of marmosets and tamarins largely consists of gums and saps, so these monkeys have evolved claw-like nails that enable them to cling to the sides of tree trunks like squirrels as well as special teeth that allow them to gnaw through bark. They also have one fewer molar than other platyrrhines, giving them a dental formula of 2:1:3:2.

    The largest of the platyrrhines are a family that include spider monkeys, woolly spider monkeys, woolly monkeys, and howler monkeys (Figure 5.28). This group of monkeys can weigh up to 9–15 kg and have evolved prehensile tails that can hold their entire body weight. It is among this group that we see semi-brachiators, like the spider monkey (Figure 5.10). To make them more efficient in this form of locomotion, spider monkeys evolved to not have thumbs so that their hands work more like hooks that can easily let go of branches while swinging. Howler monkeys are another well-known member of this group, earning their name due to their loud calls, which can be heard for miles away. To make these loud vocalizations, howler monkeys have a specialized vocal system that includes a large larynx and hyoid bone. Howler monkeys are the most folivorous of the platyrrhines and are known for spending a large portion of their day digesting their food.

    There are many other monkeys in the New World, including the gregarious capuchins (Figure 5.26) and squirrel monkeys, the pair-living titi monkeys, and the nocturnal owl monkeys. There are also the seed-eating monkeys such as saki monkeys and uakaris. In many areas across Central and South America, multiple different species of platyrrhine will share the forests, and some species will even travel together in associations that you will learn about in Chapter 6. According to molecular evidence, the diversity of platyrrhines that we see today seems to have originated about 25 million years ago (Schneider and Sampaio 2015). Figure 5.29 summarizes the key traits of platyrrhines relative to the other infraorders of Haplorrhini.

    image36-2.jpgFigure \(\PageIndex{14}\): (Clockwise from top-right) golden-headed lion tamarin, pygmy marmoset, Goeldi’s monkey, bare-eared marmoset, emperor tamarin, and common marmoset.
    image37-2.jpgFigure \(\PageIndex{15}\): (Clockwise from top right) howler monkey, woolly monkey, woolly spider monkey, and spider monkey.

    Platyrrhini traits

    Flat nose with rounded nostrils pointing to the side

    Highly arboreal

    Less sexually dimorphic on average

    2:1:3:3 dental formula*

    Polymorphic color vision*

    Platyrrhini at a glance: Summary of the key traits we use to distinguish platyrrhines. Traits indicated with an * are those with exceptions detailed in the text.

    Infraorder Catarrhini of Asia and Africa

    Infraorder Catarrhini includes Old World monkeys, apes, and humans. Non-human catarrhines are found all over Africa and South and Southeast Asia, with some being found as far north as Japan. The most northerly and southerly catarrhines are from the superfamily that includes the Old World monkeys. In contrast, apes are less tolerant of drier, more seasonal environments and so have a relatively restricted geographic range.

    image38-2.jpgFigure \(\PageIndex{16}\): A Wolf’s guenon demonstrating a typical catarrhine nose with teardrop-shaped nostrils close together and pointed downward.

    When compared to the other haplorrhine infraorders, catarrhines are distinguished by several characteristics. Catarrhines have a distinctive nose shape, with teardrop-shaped nostrils that are close together and point downward (Figure 5.30). Old World monkeys, apes, and humans also have one fewer premolar than most other primates, giving us a dental formula of 2:1:2:3 (Figure 5.31). On average, catarrhines are the largest and most sexually dimorphic group of primates. Gorillas are the largest of all living primates, with males weighing up to 220 kg. The most sexually dimorphic of all primates are mandrills. Mandrill males not only have much more vibrant coloration than mandrill females but also have larger canines and can weigh up to three times more (Setchell et al. 2001). The larger body size of catarrhines is related to the more terrestrial lifestyle of many members of this infraorder. In fact, the most terrestrial of living primates can be found in this group. Among all primate taxa, vision is the most developed in catarrhines. Catarrhines independently evolved the same adaptation as howler monkeys in having each X chromosome with sufficient genes to distinguish both reds and yellows, so all catarrhines are trichromatic. Trichromatic color vision is particularly useful to catarrhines, which are all diurnal.

    image39-2.jpgFigure \(\PageIndex{17}\): Catarrhines are distinguished in that they only have two premolars compared to the three premolars seen in most other primate taxa, including the platyrrhines shown here for comparison. In these images you can also see one of the derived traits of cercopithecoids, their bilophodont molars, which differ from the more primitive Y-5 molars that apes and humans have.

    Infraorder Catarrhini is divided into two superfamilies: Superfamily Cercopithecoidea, which includes Old World monkeys, and Superfamily Hominoidea, which includes apes and humans. Molecular estimates place the split between cercopithecoids and hominoids at about 32 million years ago (Pozzi et al. 2014), which fits well with the fossil record showing evidence of the lineages by about 25 million years ago (see Chapter 8 on primate evolution).

    Superfamily Cercopithecoidea of Africa and Asia

    Compared to hominoids, Old World monkeys have a more primitive quadrupedal body plan (discussed later in Figure 5.39), but they do have a couple of derived traits shared by all members of this group. Cercopithecoidea have bilophodont molars (“bi” meaning two, “loph” referring to ridge, and “dont” meaning tooth). Referring back to Figure 5.31, you will see how the molars of cercopithecoids have four cusps arranged in a square pattern and have two ridges connecting them. It is thought that this molar enabled Old World monkeys to eat a wide range of foods, thus allowing them to live in habitats that apes cannot. The other key derived trait that all cercopithecoids share is having ischial callosities (Figure 5.32). The ischium is the part of your pelvis that you are sitting on right now (see Appendix A: Osteology). In Old World monkeys, this part of the pelvis has a flattened surface that, in living animals, will have callused skin over it. These function as seat pads for cercopithecoids, who often sit above branches when feeding and resting.

    image40-1.jpgFigure \(\PageIndex{18}\): The second derived trait of cercopithecoids are their ischial callosities, shown here on a crested black macaque.
    image41.pngFigure \(\PageIndex{19}\): Geographic distribution of the Old World monkeys. Catarrhines have the widest geographic distribution due to the success of cercopithecoid monkeys who are found all across Africa and Asia.
    image42-2.jpgFigure \(\PageIndex{20}\): Silver leaf monkey infants are born with orange fur, dramatically contrasting the adult coat color of their mothers. After a few months, the infants gradually change color to that of their parents.

    The cercopithecoid monkeys are the most geographically widespread group of non-human primates (Figure 5.33). Since their divergence from hominoids, this monkey group has increased in numbers and diversity. In part, their success over hominoids is due to the faster reproductive rates of cercopithecoids relative to hominoids. On average, Old World monkeys will reproduce every one to two years, whereas hominoids will reproduce once every four to nine years, depending on the taxon.

    image43-2.jpgFigure \(\PageIndex{21}\): Proboscis monkeys are one of several “odd-nosed” leaf monkeys. Male proboscis monkeys, like the one shown here, have large, pendulous noses. Female proboscis monkey noses are much smaller; in this species nose size is a sexually dimorphic trait.

    Cercopithecoidea is split into two groups, the leaf monkeys and the cheek-pouch monkeys. Both groups coexist in Asia and Africa; however, the majority of leaf monkey species live in Asia with only a few taxa in Africa. In contrast, only one genus of cheek-pouch monkey lives in Asia, and all the rest of them in Africa. As you can probably guess based on their names, the two groups differ in terms of diet. Leaf monkeys are primarily folivores, with some species eating a significant amount of seeds. Cheek-pouch monkeys tend to be more frugivorous or omnivorous, with one taxon, geladas, eating primarily grasses. The two groups also differ in some other interesting ways. Leaf monkeys tend to produce infants with natal coats—infants whose fur is a completely different color from their parents (Figure 5.34). Leaf monkeys are also known for having odd noses (Figure 5.35), and so they are sometimes called “odd-nosed monkeys.” Cheek-pouch monkeys are able to pack food into their cheek pouches (Figure 5.36), thus allowing them to move to a location safe from predators or aggressive individuals of their own species where they can eat in peace.

    image44-2.jpgFigure \(\PageIndex{22}\): This bonnet macaque has filled its cheek pouches with food. This adaptation is useful in transporting food to a safer location to eat.

    SPECIAL TOPIC: PRIMATES IN CULTURE AND RELIGION

    image45-2.jpgFigure \(\PageIndex{23}\): Because of important monkey-like figures in the Hindu religion, macaques are protected in India and often live near temples where they are fed by local peoples.

    In the introduction to this chapter, I mentioned the innate affinity that humans have toward non-human primates even when we do not fully understand our exact relationship to them. In fact, recognition of similarities between humans and other primates is very ancient, dating back far earlier than Linnaeus. For many of us, we only ever get to see primates in zoos and animal parks, but in many areas of the world, humans have coexisted with these animals for thousands of years. In areas where humans and primates have a long, shared history, non-human primates often play key roles in creation myths and cultural symbolism.

    Hamadryas baboons feature significantly in Ancient Egyptian iconography. Ancient Egyptian deities and beliefs transformed over time, as did the role of hamadryas baboons. Early on, baboons were thought to represent dead ancestors, and one monkey deity, called Babi or Baba, was thought to feed off of dead souls. Later, baboons became the totem animal for Thoth, the deity of science, writing, wisdom, and measurement, who also wrote the book of the dead. Sunbathing hamadryas baboons led ancient Egyptians to associate them with Ra, the sun god, who was the son of Thoth. During mummification, human organs were removed and put into canopic jars, one of which was topped with the head of the baboon-headed god, Hapi. Hamadryas baboons were also often kept as pets, as depicted in hieroglyphics, and occasionally mummified as well.

    On Madagascar, indris and aye-ayes play roles in the creation myths and omens of local people. There are many myths regarding the origins of indris and their relationship to humans, including one where two brothers living in the forest separated, with one brother leaving the forest and becoming a human while the other stayed in the forest to become the indri. Indris are considered sacred and are therefore protected, due to their similarities to humans in having long legs, no tail, and upright posture. Unfortunately, the aye-aye is not treated with the same reverence. Aye-ayes, due to their unusual appearance, are thought to be omens of death. They are usually killed when encountered because it is believed that someone will die if an aye-aye points at them.

    In India, monkeys play a key role in the Hindu religion. Hanuman, who resembles a monkey, is a key figure in the Ramayana. Hanuman is thought to be a guardian deity, and so local monkeys like Hanuman langurs and macaques are protected in India (Figure 5.37). In Thailand, where Hinduism is also practiced, the Hindu reverence for monkeys extends to “monkey feasts,” where large quantities of food are spread out in gratitude to the monkeys for bringing good fortune.

    The people of Japan have coexisted with Japanese macaques for thousands of years, and so monkeys play key roles in both of the major Japanese religions. In the Shinto religion, macaques are thought of as messengers between the spirit world and humans and monkey symbols are thought to be good luck. The other major religion in Japan is Buddhism, and monkeys play a role in symbolism of this religion as well. The “Three Wise Monkeys” who see no evil, speak no evil, and hear no evil derive from Buddhist iconography of monkeys.

    In the New World, monkeys feature often in Mayan and Aztec stories. In the Mayan creation story, the Popol Vuh, the “hero brothers” are actually a howler monkey and a spider monkey, who represent ancestors of humans in the story. In the Aztec religion, spider monkeys are associated with the god of arts, pleasure, and playfulness. A spider monkey is also represented in a Peruvian Nazca geoglyph, a large design made on the ground by moving rocks.

    In many of these regions today, the relationships between humans and non-human primates are complicated. The bushmeat and pet trades make these animals valuable at the expense of many animals’ lives, and in some areas, non-human primates have become pests who raid crop fields and consume valuable foods. All of this has led to the development of a new subarea of anthropology called Ethnoprimatology, which involves studying the political, economic, symbolic, and practical relationships between humans and non-human primates. This field highlights the particular challenges for humans of having to coexist with animals with whom we share so much in common. It also provides insight into some of the challenges facing primate conservation efforts (see Appendix A: Primate Conservation).

    Superfamily Hominoidea of Africa and Asia

    Figure \(\PageIndex{23}\): Geographic distribution of apes across Central and West Africa, and Southeast Asia. Hominoids overlap geographically with cercopithecoid monkeys but have a lower tolerance for seasonal environments and so are found only in tropical forests across these regions.

    The Superfamily Hominoidea of Africa and Asia (Figure 5.38) includes the largest of the living primates, apes and humans, but our superfamily differs from other primates in some other key ways as well. When compared to cercopithecoids, hominoids have more primitive teeth. Whereas Old World monkeys have bilophodont molars, hominoids have , which feature five cusps separated by a “Y”-shaped groove pattern (Figure 5.31). The Y-5 molar was present in the common ancestors of hominoids and cercopithecoids, thus telling us it is the more primitive molar pattern of the two. Where hominoids differ the most from other primates, however, is in our body plans. This is due to the unusual form of locomotion that hominoids are adapted for, brachiation (Figure 5.39).

     

    Quadrupedalism

    Brachiation

    Arm length vs. leg length

    About equal

    Arms are longer

    Shoulder position

    More on the front

    Out to the side

    Ribcage shape

    Deep front-to-back

    Narrow side-to-side

    Shallow front-to-back

    Wide side-to-side

    Length of lower back

    Long

    Short

    Collar bone length

    Short

    Long

    Ulnar olecranon process

    Long

    Short

    Ulnar styloid process

    Long

    Short

    Tail

    Short to long

    None

    Figure 5.39 Quadrupedalism vs. brachiation: Summary of the key anatomical differences between a quadrupedal primate and one adapted for brachiation. To view and compare these traits using photos of bones, check out the interactive skeletal websites listed under the “Further Explorations” section at the end of this chapter.

    To successfully swing below branches, many changes to the body needed to occur. The arms of a hominoid are much longer than the legs in order to increase reach, and the lower back is shorter and less flexible to increase control when swinging. The torso, shoulders, and arms of hominoids have evolved to increase range of motion and flexibility (Figure 5.9). The clavicle, or collar bone, is longer in order to stabilize the shoulder joint out to the side, thus enabling us to rotate our arms 360 degrees.Our rib cages are wider side to side and shallower front to back than those of cercopithecoids and we do not have tails, as tails are useful for balance when running on all fours but not useful when swinging. Hominoids also have modified ulnae, one of the two bones in the forearm (see Appendix A: Osteology). At the elbow end of the ulna, hominoids have a short olecranon process, which allows for improved extension in our arms. At the wrist end of the ulna, hominoids have a short styloid process, which enables us to have very flexible wrists, a trait critical for swinging. Both the olecranon process and styloid process are long in quadrupedal animals who carry much of their weight on their forelimbs when traveling and who therefore need greater stability rather than flexibility in those joints.

    Apes and humans also differ from other primates in behavior and life history characteristics. Hominoids all seem to show varying degrees of female dispersal at sexual maturity. Dispersal refers to leaving the area or group where an individual was born. As you will learn about in Chapter 6, it is more common that males leave. Indeed, some apes show males dispersing in addition to females, but the broader tendency for female dispersal in hominoids is a bit unusual among primates. Our superfamily is also characterized by the most extended life histories of all primates. All members of this group live a long time and take a long time to grow and start reproducing. Hominoids also reproduce much less frequently compared to cercopithecoid monkeys. The slow pace of this life history is likely related to why hominoids have decreased in diversity since they first evolved. In the past, hominoids were tremendously diverse in both geography and adaptations. Today, there are only five types of hominoids left: gibbons and siamangs, orangutans, gorillas, chimpanzees and bonobos, and humans.

    Infraorder Catarrhini

    Downward facing, tear-drop shaped nostrils, close together

    Arboreal and more terrestrial taxa

    On average, largest primates

    On average, most sexually dimorphic taxonomic group

    2:1:2:3 dental formula

    All trichromatic

    image47-2.jpg

    Superfamily Cercopithecoidea

    image48-1.jpg

    Superfamily Hominoidea

    Wide geographic distribution

    Bilophodont molars

    Ischial callosities

    Reproduce every 1-2 years

    Tropical forests of Africa and Asia

    Y-5 molars

    Adaptations for brachiation

    Reproduce every 4-9 years

    Figure 5.40 Catarrhini at a glance: Summary of key traits of the Infraorder Catarrhini as well as the characteristics used to distinguish between the two superfamilies within this group.

    Family Hylobatidae of Southeast Asia

    image49-2.jpgFigure \(\PageIndex{24}\): Siamangs are the largest of the Hylobatidae family. They are all black and, as you can see inflated in this photo, have a throat sac that they use to give loud calls.

    The number of genera in this group has been changing in recent years, but the taxa included can broadly be discussed as gibbons and siamangs. Both are found across Southeast Asian tropical forests. These are the smallest of the hominoids and so are sometimes referred to as the “lesser apes.” Gibbons weigh, on average, about 13 pounds and tend to be more frugivorous, whereas siamangs are about twice the size of gibbons and are more folivorous. Unlike the larger-bodied apes (orangutans, chimps, bonobos, and gorillas) who make nests to sleep in every night, gibbons and siamangs will develop callused patches on their ischium resembling ischial callosities. There are many different gibbon species that vary in their coloration and markings. Siamangs, however, are all black with big throat sacs that are used in their exuberant vocalizations (Figure 5.41). Both gibbons and siamangs live in pairs with very little sexual dimorphism, although males and females do differ in coloration in some species.

    Pongo of Southeast Asia

    image50-2.jpgFigure \(\PageIndex{25}\): A female orangutan and her infant.
    image51-2.jpgFigure \(\PageIndex{26}\): A flanged adult male. Male orangutans are about twice the size of females, and in these photos you can also see the sexual dimorphism in coat length, cheek flanges and throat sac in the male.

    The Genus Pongo refers to orangutans. These large red apes are found on the islands of Borneo and Sumatra in Southeast Asia. There are two well-known species of orangutan, one on each island. Recently, a third, very rare species was discovered in Southern Sumatra (Nater et al. 2017). Orangutans are highly frugivorous but will supplement their diet with leaves and even bark when fruit is less available. As mentioned earlier, orangutans are the only diurnal, solitary taxon among primates and are extremely slow to reproduce, producing only one offspring about every seven to nine years. They are highly sexually dimorphic (Figure 5.42), with fully developed, “flanged” males being approximately twice the size of females. These males have large throat sacs; long, shaggy coats; and cheek flanges.The skulls of male orangutans often feature a sagittal crest, which is believed to function as both additional attachment area for chewing muscles but also in sexual competition (Balolia et al. 2017). An unusual feature of orangutan biology is male bimaturism. Male orangutans are known to delay maturation until one of the more dominant, flanged males disappears. The males that delay maturation are called “unflanged” males, and they can remain in this state for their entire life. Unflanged males resemble females in their size and appearance and will sneak copulations with females while avoiding the bigger, flanged males. Flanged and unflanged male orangutans represent alternative reproductive strategies, both of which successfully produce offspring (Utami et al. 2002).

    Gorilla of Africa

    image53-2.jpgFigure \(\PageIndex{27}\): A female gorilla and her offspring.
    image52-2.jpgFigure \(\PageIndex{28}\): A silverback male. Male gorillas are about twice the size of females, but also differ from females in having a large sagittal crest, and silver back, which appears as they mature.

    There are several species of gorillas that can be found across Central Africa. Gorilla males, like orangutan males, are about twice the size of female gorillas (Figure 5.43). When on the ground, gorillas use a form of quadrupedalism called , where the fingers are curled under and the weight is carried on the knuckles. Male gorillas have a large sagittal crest and larger canines compared with females. Adult male gorillas are often called “silverbacks” because when they reach about twelve to thirteen years old, the hair on their backs turns silvery gray. Gorillas typically live in groups of one male and several females. Gorillas are considered folivorous, although they can be more frugivorous depending on fruit seasonality (Remis 1997).

    Pan of Africa

    image54.jpgFigure \(\PageIndex{29}\): Bonobo, Pan paniscus. You can see the distinctive hair-part on this bonobo.

    The Genus Pan includes two species: Pan troglodytes (the common chimpanzee) and Pan paniscus (the bonobo). These species are separated by the Congo River, with chimpanzees ranging across West and Central Africa and bonobos located in a restricted area south of the Congo River. Chimpanzees and bonobos both have broad, largely frugivorous diets and similar social groups. The two species differ morphologically in that bonobos are slightly smaller, have their hair parted down the middle of their foreheads, and are born with dark faces (Figure 5.44). In contrast, chimpanzees do not have the distinctive parted hair and are born with light faces which darken as they mature (Figure 5.45). Chimpanzees and bonobos live in a grouping called a fission-fusion community, which you will learn more about in Chapter 6. Both species are moderately sexually dimorphic, with males about 20% larger than females. When on the ground, chimpanzees and bonobos knuckle-walk like gorillas do.

    image55.jpgFigure \(\PageIndex{30}\): A common chimpanzee, Pan troglodytes, female and her offspring. Note the pink face of the youngest individual. Bonobos are born with dark-skinned faces, but chimpanzees are born with pink faces that darken with age.

    Homo

    The last member of the Hominoidea to discuss is our own taxon, Genus Homo. Humans differ from apes in many aspects of our morphology, behavior, and life history, all of which you will be learning about in later chapters. One of the objectives of this chapter, however, and of biological anthropology in general, is to understand our place in nature. This means looking for the aspects of human biology that lead us to place humans within the taxonomic diversity we have just discussed. To accomplish this, we not only consider how humans are different from other species but also examine the traits that unite us with the other primates, our similarities—that is our focus here.

    There are clear similarities between humans and the other apes in our morphology and life history. Like other hominoids, humans lack a tail and possess upper-body adaptations for brachiation. While our lower body has been modified for a bipedal gait, we are still able to swing from branches or “monkey bars,” or throw a fastball, all thanks to our mobile shoulder joint. Humans, like other hominoids, also have a Y-5 cusp pattern on our molars. As discussed earlier, all hominoids have an extended life history, taking a long time to grow and develop, and have a long life span. Humans, too, exhibit these same characteristics. Lastly, while humans show a great deal of variation across cultures, many human societies show patterns of female dispersal in which males stay in the group into which they were born while females leave (Burton et al. 1996).

    Among the hominoids, humans show particular affinities with other members of the African Clade, Pan and Gorilla. Humans share over 96% of our DNA with gorillas (Scally et al. 2012), and over 98% with Pan (Ebersberger et al. 2002). Even without this strong genetic evidence, the African Clade of hominoids share many morphological similarities. These shared traits include eye sockets that are slightly farther apart and are more square or rounded compared to the closely placed, ovoid eyes of orangutans. Also, the cheekbones of the African clade sweep backward compared to the more flattened orangutan cheekbones. Today, Pan and Gorilla knuckle-walk when on the ground, and it has been suggested that the last common ancestor of chimpanzees, bonobos, gorillas, and humans shared this trait (Richmond et al. 2001).

    Our closest living relatives today are chimpanzees and bonobos. Because of our close relationship, humans share many additional traits in common with Pan. Humans, chimpanzees, and bonobos all live in similar social groups that are characterized by territoriality and male cooperation, among other things. Chimpanzee males are well-known to cooperate in hunting, a common trait across human societies as well. As you will learn more about in the next chapter, chimpanzee populations have also been observed to make and use tools for different purposes, not unlike what humans do.


    This page titled 5.3: Primate Diversity is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Beth Shook, Katie Nelson, Kelsie Aguilera, & Lara Braff, Eds. (Society for Anthropology in Community Colleges) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.