ANT 151
3.10 - Family Cebidae
3.10 - Family Cebidae Family Cebidae This family is subdivided into three subfamilies: Subfamily Cebinae, Subfamily Aotinae and Subfamily Callitrichinae. Subfamily Cebinae Commonly called capuchins and squirrel monkeys, there are three genera in this subfamily: Cebus - capuchin monkeys Sapajus - robust capuchin monkeys (image at right) Saimiri - squirrel monkeys Morphology Semi-prehensile tails (no tactile pad and typically use their tails for balance rather than hanging their full body weight by their tail) Fairly large-brained (especially capuchins) Quadrupedal Saimiri smaller than Cebus Saimiri has interorbital septum (opening in the skull between the eye sockets) Diet These monkeys are the most omnivorous of the platyrrhines Saimiri eats about 50% insects and 50% fruit Behavior Medium (capuchins) to large (squirrel monkeys) multi-male, multi-female groups Diurnal Form polyspecific associations where capuchins and squirrel monkeys will travel together in the forest while feeding No social grooming in Saimiri Some capuchin taxa have been seen to use tools (e.g. nut cracking like in the video below)
Strepsirrhini Suborder
As you learned, when two lineages split from one another, one will become more derived and the other will remain more primitive in keeping more of the ancestral traits. This is certainly true when we look at the differences between the two primate suborders. Strepsirrhines differ from haplorrhines in many ways, most of which involve retaining primitive traits from the last common ancestor of primates. As a result, all of the traits discussed below are primitive traits, but strepsirrhines do have two key derived traits (images below) that evolved after they diverged from the haplorrhines. Derived traits of Suborder Strepsirrhini The two derived traits are the grooming claw (photo on the left below), which is on the second digit of each foot, and the tooth comb (photo on the right below), located on the lower, front teeth. In most strepsirrhines, there are six teeth in the toothcomb—the four incisors and the two canines. Other traits of Suborder Strepsirrhini In addition to their two key derived traits, strepsirrhines differ from haplorrhines in many other areas of their anatomy and behavior. Cranial traits 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 (smell) 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. Strepsirrhines have less convergent eyes than haplorrhines, and all have postorbital bars whereas haplorrhines have full postorbital closure (see image from previous module). 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. This trait is thought to be primitive among mammals as a whole. Compared to haplorrhines, strepsirrhines also have more primitive traits of their skulls such as an unfused mandibular symphysis and frontal bone, a relatively small brain case, and primitive jaws and molars. In addition, the position of the carotid foramen is farther back and strepsirrhines have an ear ring rather than a tube like most haplorrhines. You can see images and more details of these differences here. Postcranial traits 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 can be found in the Suborder Strepsirrhini. In order to facilitate this form of locomotion, strepsirrhines are generally smaller bodied than haplorrhines and many have modified ankle morphology that allows them to invert their ankles better for clinging to vertical supports. With one exception (Lemur catta) strepsirrhines are also highly arboreal and spend very little time on the ground. Ecology and Behavior 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. The smaller bodies of strepsirrhines is also reflected in their diet, with many having a diet consisting of insects and fruit, with few taxa eating primarily leaves. Members of this subfamily are not sexually dimorphic (unlike most haplorrhines), although some are sexually dichromatic (males and females are different colors). Many strepsirrhines also park their infants in nests rather than carry them while females go off to forage. Strepsirrhines can be found all across the Old World: in Asia, Africa, and on the island of Madagascar. The Suborder Strepsirrhini is divided into two groups: (1) the lemurs of Madagascar and (2) the lorises, pottos, and galagos of Africa and Asia. The map below shows their geographic distribution. Reproduction/Offspring Finally, strepsirrhines differ from haplorrhines in some taxa having multiple sets of nipples and the ability to have small litters. The morphology of the uterus of strepsirrhines differs from haplorrhines in that lemurs and lorises have a bicornate (two-horned) uterus (image below, left) and an epitheliochorial placenta (which has more layers separating the mom and fetus compared to a haplorrhine (which has a hemochorial placenta).
3.9 - Family Atelidae
Family Atelidae This family consists of one subfamily, Atelinae. Subfamily Atelinae There are four genera in this subfamily: Alouatta - howler monkeys (top right image) Ateles - spider monkeys (top left image) Brachyteles - woolly spider monkeys (bottom right image) Lagotrhix - woolly monkeys (bottom left image) Morphology: Largest of the platyrrhines True prehensile tails which have tactile pads on the underside for grip Semi-brachiators, often using their tail as a fifth limb Some lack thumbs, others schizodactylous Some females have hypertrophied clitoris and so look superficially like males Alouatta specialized for folivory, loud-calling (hence its name) To see spider monkeys moving around in the trees with their prehensile tails, watch the short video below. Diet: Ateles and Lagothrix are highly frugivorous Alouatta is folivorous Brachyteles eats both leaves and fruit Behavior: Ateles and Brachyteles have a fission-fusion social system Lagothrix lives in multimale, multifemale groups Alouatta live in mostly small single-male, multi-female or multi-male, multi-female groups All are diurnal and arboreal
Family Cheirogaleidae
Family Cheirogaleidae The Cheirogaleidae are a group of small, nocturnal strepsirrhines on Madagascar. They are five, not particularly well known genera: Microcebus - Mouse lemur (image at right) Cheirogaleus - Dwarf lemur Mirza - Giant mouse lemur Phaner - Fork-marked lemur Allocebus - Hairy-eared dwarf lemur Morphology This family includes the smallest of all living primates, Microcebus which weighs about 100 g, like a mouse. Cheirogaleidae are characterized by having three sets of nipples (and the ability to have small litters) and highly seasonal adaptations. Outside of the short breeding season, the vaginas of female cheirogaleids close up. In addition, during several months of the year, members of this family store fat (some in their tail, some all over their bodies) in order to undergo torpor (a kind of hibernation in which their metabolism slows) until the fruiting season returns. Diet All but Phaner have diet of fruits, nectar, insects and small vertebrates. Phaner, the fork-marked lemur, is a gum specialist and has all of the traits for this dietary type discussed in the last module. Behavior As mentioned above, not much is known about this family (they are challenging to study due to their small size and nocturnal habits), but they are known to be solitary foragers who sleep in shared nests/tree holes during the day.
Family Daubentoniidae
Family Daubentoniidae The most unique of all strepsirrhines is Daubentonia, the only genus in the Family Daubentoniidae. There is also only one living species in this group, Daubentonia madagascariensis. It is believed that this lineage was the earliest to separate from the other Lemuroidea, thus explaining its many unique characters. Morphology Daubentonia possesses many unusual characteristics: Dental formula 1013/1003, with gliriform incisors (ever-growing, like in rodents) Insecting claw on third digit of hands Relative brain size equivalent to monkeys and apes Sexual swellings at estrus (like some catarrhines) Largest nocturnal primate (it has extinct relatives that were even larger) Diet The diet of Daubentoniidae consists of animal matter (eggs, insects, etc.), seeds, fruit, and nectar. Behavior As mentioned above, this taxon is nocturnal. It is also a solitary forager that does not seem to exhibit any social grooming and who sleeps in nests made of leaves (sometimes shared with others).
Family Galagidae 3.3 - Superfamily Lorisoidea The Lorisoidea subdivides into two families: Family Galagidae and Family Lorisidae. The two families of lorisoids split about 30-37 mya, according to molecular evidence. The galagids and lorisids differ most notably in their locomotion, as you will see.
Family Galagidae Commonly called bushbabies due to their vocalization that sounds like a baby crying, galagos are found in the forests of central Africa and include six genera: Galago - "Lesser" galagos Galagoides - Western Dwarf galagos Sciurocheirus - Squirrel galagos Otolemur - "Greater" galagos Euoticus - Needle-clawed galagos Morphology This family is known for being fast-moving quadrupedal leapers and bounders (similar to a squirrel). They have long tails, long hind limbs, and specialized ankles. Diet Galagos eat a varied diets of insects and fruit, but all include at least some gum in their diet. The smaller taxa (Galagoides) eat a lot of insects, the medium-sized taxa (Galago, Euoticus) eat a lot of gum, and the largest taxa (Sciurocheirus, Otolemur) eats more fruit. Behavior Galagos evade predators through quick locomotion and use vocal and olfactory communication with others of their species. Although they are solitary foragers, galagos commonly co-sleep in shared nests. Like all lorisoids, galagos are nocturnal and so they rely on their mobile ears and keen sense of smell to locate mobile prey in the dark.
Family Indriidae
Family Indriidae The largest of all lemuroidea are the indriids. There are three genera in this family, including: Indri - Indri Propithecus - Sifaka (image at right) Avahi - Woolly lemurs Morphology Members of this family are distinguished in having a reduced dental formula (2123) with only four teeth in their tooth combs rather than six. They are also all specialized for vertical clinging and leaping. Indri is the largest of the living lemurs and differs from other VCL taxa in lacking a long tail. Diet All Indriidae are folivorous, a relatively rare dietary type among the strepsirrhines. Behavior Indri and Avahi are pair-living while Propithecus lives in small multimale, multifemale groups. Indri and Propithecus are diurnal, but Avahi is nocturnal.
3.4 - Superfamily Lemuroidea -Family Lemuridae The Lemuroidea are found exclusively on the island of Madagascar. The world's 4th largest island, Madagascar is the size of California and Oregon combined. It is located off the east coast of Africa, and has been separated from Africa for about 165 my and from India for about 80-90 my. Madagascar was already an island when lemuroid ancestors arrived, and today they are the only non-human primate to live there.
Family Lemuridae This family includes the most well-known of the lemuroidea and probably the ones that people would most easily recognize. There are five genera in this family, including: Lemur - Ring-tailed lemur Hapalemur - Bamboo lemur Prolemur - Greater bamboo lemur Eulemur - Brown lemurs (although not all are brown) Varecia - Ruffed lemurs (image at right) Morphology This family includes medium-sized lemurs who are mostly quadrupedal (Lemur, Eulemur, Varecia), except Hapalemur and Prolemur which are vertical clinger and leapers. For the most part, lemuroidea show no sexual dimorphism, although some species of Eulemur are sexually dichromatic with males and females having different coloration. Diet Lemur and Eulemur are considered omnivorous, while Varecia is highly frugivorous and serves as an important seed disperser for many plants. Hapalemur and Prolemur are the most unusual in being bamboo specialists that are able to metabolize the cyanide that naturally occurs in bamboo. Behavior We see a range of social groupings in this family: Lemur and Eulemur live in multi-male, multi-female groups, Varecia sometimes lives in pair-living and sometimes in fission-fusion type groups, and Hapalemur is pair-living. Most members of the Lemuridae are considered diurnal, but some are cathemeral. All are highly vocal in communications with each other in their arboreal lifestyles. Of all strepsirrhines, Lemur is the most terrestrial, spending about 30% of their time on the ground.
Family Lepilemuridae
Family Lepilemuridae Although there are many species, all of the sportive lemurs, as they are called, fall into one genus, Lepilemur. As with the cheirogaleids, we do not know much about this group. Morphology They are most well-known for their specialized adaptations for vertical clinging and leaping. Members of this family are also unusual in having a 0133/2133 dental formula. This dental formula reflects their absence of upper incisors, a trait also seen in extinct members of this family. Diet Lepilemur are all folivorous. Despite their small size, sportive lemurs are able to get enough nutrition out of their folivorous diet by practicing caecotrophism. (Links to an external site.) Behavior The Lepilemuridae are all nocturnal, solitary foragers.
Family Lorisdae 3.3 - Superfamily Lorisoidea
Family Lorisdae This family includes four genera, the first two are found in Africa, and the second two are from South and Southeast Asia. Perodicticus (pottos) Arctocebus (angwantibos) Loris (slender loris) Nycticebus (slow loris) Morphology Unlike their active, quadrupedal relatives, lorisids are slow, cautious, quadrupedal climbers. Their limbs are more even in length, and they lack long tails. In each region where this family is found, one genus is more "gracile" with thin, long limbs and the other is more "robust" in its build. In Africa, the potto is more robust and the angwantibo is more gracile, while in Asia, the slow loris is more robust and the slender loris is more gracile. While some members of the Lorisidae have reduced second digits on their hands, all members of this taxon have large orbits that are highly convergent. Diet Lorisidae seem to emphasize slow-moving insects and fruit in their diet. Some lorisids eat toxic insects which causes their saliva to become toxic. This saliva is then used to coat and protect infants who are often parked in nests while mothers are foraging. In general, the smaller, slender types (Arctocebus, Loris) use more insects and the larger, robust types (Perodicticus, Nycticebus) use more fruit. Behavior Lorisids evade predators through crypsis (avoiding being detected). Members of this family are specialized for being still for prolonged periods to avoid attracting attention. Lorisidae use more olfactory communication than vocalizations, but they, too, are nocturnal, solitary foragers that co-sleep.
Subfamily Aotinae
Subfamily Aotinae The owl monkeys, as they are called, consist of one genus, Aotus. These nocturnal monkeys are broadly separated into two groups: the grey-necked owl monkeys (north of the Amazon river) and the red-necked owl monkeys (south of the Amazon river). Morphology Large eyes with no tapetum lucidum Monomorphic with no sexual dimorphism Monochromatic! Diet Primarily frugivorous, few leaves and insects Behavior Frequently use scent-marking Only nocturnal monkey today Pair-living and monogamous with significant paternal care Territorial against other pairs
Subfamily Callitrichinae
Subfamily Callitrichinae There are now seven genera in the Callitrichinae, these include: Callimico - Goeldi's monkey Cebuella - Pygmy marmoset Mico - Marmosets Callithrix - Atlantic forest marmosets Saguinus - Tamarins (image at right) Leontopithecus - Golden lion tamarins Leontocebus - Saddle-back tamarins Morphology Smallest of the platyrrhines 2132 dental formula, except Callimico who has 2133 Re-evolved claws - modified nails Diet Marmosets specialize in eating gum and sap Other callithrichines are more fruit/insect-eating Behavior Small family groups Monogamous, polygynous or polyandrous Both sexes disperse Reproductive suppression where only one female reproduces at a time Paternal and sibling care for infants (usually twins, except Goeldi's monkey) Aggressive toward other groups of their own species Often form polyspecific associations with other callitrichines
Subfamily Pitheciinae
Subfamily Pitheciinae The pitheciines are among the least well known platyrrhine monkeys partly because some of them prefer to live high in the forest in swampy areas where it is difficult to traverse. This group includes three genera: Pithecia - Saki monkeys (image at right) Chiropotes - Bearded saki monkeys Cacajao - Uakaris Morphology: The most distinctive features of this group have to do with their dietary adaptations. Adapted for seed predation Large, procumbent incisors Tusk-like canines Diet: Seeds and fruit primarily Behavior: Little is known about their behavior other than Pithecia lives in small groups or pairs and Cacajao and Chiropotes seem to live in large groups. Below is a short video showing a bald-headed uakari.
3.6 - Infraorder Tarsiiformes
Suborder Haplorrhini is divided into three Infraorders: Infraorder Tarsiiformes - Tarsiers Infraorder Platyrrhini - New World monkeys Infraorder Catarrhini - Old World monkeys, apes and humans Infraorder Tarsiiformes Today, the Infraorder Tarsiiformes includes only one genus, Tarsius. Tarsiers are small-bodied primates that live in Southeast Asian forests and possess an unusual collection of traits that have led to some debate about their position in the primate taxonomy. Traits shared with Haplorrhines They are widely considered members of the haplorrhine group because they share several key derived traits with monkeys, apes, and humans, including: Dry noses Fovea Not having a tapetum lucidum More convergent eyes Reduced olfactory bulb Fused frontal bone Haemochorial placenta Traits shared with Strepsirrhines Tarsiers also have some traits that are more like strepsirrhines, although it is unclear whether these are symplesiomorphic or analogous. These traits include: Being nocturnal Having mobile ears Simple, sharp teeth Unfused mandible Bicornate uterus Multiple sets of nipples Solitary foragers Small (100-150 g) No sexual dimorphism Unique traits of Tarsiiformes Tarsiers also have many traits that are unique, including: Mostly closed post-orbital plate (image at right) - not fully closed like other haplorrhines but not a bar like strepsirrhines Very large eyes - each eye of a tarsier is larger than its brain Two grooming claws on each foot Reduced number of teeth 2133/1133 dental formula Faunivorous - tarsiers are the only primate not to each any vegetable matter, their diet consists entirely of animal matter like insects, larvae, eggs, etc. Highly specialized vertical clinger and leapers - their name derives from their modified ankle (tarsal) bones for leaping and the two lower leg bones (fibula and tibia) are fused for the lower third of their length Ability to rotate their heads around 180 degrees, like an owl - this is useful for locating insect prey at night Trouble with Tarsiers Because of their unusual mix of traits, tarsiers have been difficult to classify, historically. If one is using a grade classification, then tarsiers seem to be more like strepsirrhines in their nocturnal, solitary, insect-focused lifestyles. However, if we look at derived traits, then tarsiers do share some key synapomorphic traits with Haplorrhini. More recently, genetics have shown that tarsiers do share a slightly closer relationship with monkeys, apes and humans, confirming a Haplorrhini classification.
Strepsirrhine Superfamilies: Superfamily Lemuroidea
Superfamily Lemuroidea The lemurs are the only non-human primates on Madagascar, and so they have been able to diversify in the absence of competition with other primates. As a result, the Lemuroidea are much more diverse than the Lorisoidea. Many Malagasy strepsirrhines are nocturnal, but plenty of others are diurnal or cathemeral. 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. Lemurs are also more 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. It is also among the lemurs that we see some of the 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.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. Like mammals in general, most primates show male dominance over females because males 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.
Superfamily Lorisoidea
Superfamily Lorisoidea 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. 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.
3.8 - Family Pithecidae
The New World monkeys are subdivided into three families and six subfamilies, as seen on the diagram on the previous page. The next few pages will go into more detail about the diversity of these platyrrhine groups. Family Pitheciidae This family is divided into two subfamilies. Subfamily Callicebinae Commonly referred to as titi monkeys, this group has been split into several different genera, including Callicebus Plecturocebus Cheracebus Morphology: These small monkeys are thought to have morphology similar to the ancestral platyrrhines. Today, these taxa are characterized by: Monomorphic - no sexual dimorphism Tail-twining - the male and female pair will twine their tails when sitting together (see image at right) Quadrupedal Diet: Mostly fruit, with leaves and some insects Behavior: Diurnal Pair-living and socially monogamous Territorial Heavy paternal care Strong pair-bond ----------------------------------
3.7 - Infraorder Platyrrhini
The platyrrhines, also commonly called New World monkeys, are the only non-human primates in Central and South America and so, like the lemurs of Madagascar, have diversified into a variety of forms in the absence of competition. Key traits of the Platyrrhini When comparing the traits of the platyrrhines, we typically use catarrhines as a contrast. This is for two reasons: 1) tarsiers are highly unusual in many aspects of their morphology and behavior, as you just learned, and 2) we have strong morphological and genetic evidence that platyrrhines and catarrhines shared a long period of common ancestry after tarsiers diverged and before they split from one another. So, for the comparisons below, platyrrhines are compared to catarrhines. Cranial traits 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. This nose shape is very different from what we see in catarrhines, the group that includes Old World monkeys, apes, and humans which you will learn about in the next module. The dentition of platyrrhines is primitive in retaining a 2133 dental formula (callitrichines are an exception, as you will read about) and lacking a large diastema for the canine as we see in catarrhines. Most also lack a hypoconulid (the distal-most cusp (Links to an external site.)) on the lower molars. As seen in the image above, the skulls of platyrrhines differ from catarrhines in having: Tympanic ear ring (catarrhines have a tube) Parietal and zygomatic bones articulate (in catarrhines the frontal and sphenoid bones articulate) Cranial sutures fuse late (these fuse relatively early in catarrhines). Postcranial traits On average, Platyrrhini are smaller and less sexually dimorphic than catarrhines, and all but one are highly arboreal (many Old World monkeys and apes spend significant time on the ground). Platyrrhines have developed some interesting postcranial traits that distinguish them from catarrhines as well. Some of the platyrrhines have developed truly prehensile tails with which they hang their full body weight from while moving and feeding, and others have evolved nails which function like claws to allow them to grip large-diameter trees and branches. Many of the platyrrhines also show reduced pollex (thumb) opposability, with some showing schizodactyly in which the index finger and thumb are somewhat separated from the other fingers (see image at right) and others lacking thumbs altogether! Ecology and Behavior As mentioned above, platyrrhines are highly arboreal, very rarely coming to the ground. Only one genus (Cebus) spends about 30% of its time on the ground. All platyrrhines are diurnal, except for the owl monkeys (Aotus), who is nocturnal. Small-bodied platyrrhines often use scentmarking, not as much as strepsirrhines but catarrhines do not use scent at all. All of the platyrrhines live in groups as well, some in pairs, some in small multi-male, multi-female groups, some in large multi-male, multi-female groups, and some in fission-fusion groups. To review the types of social systems in primates, visit this page. Other Traits of the Platyrrhini The New World monkeys also differ from catarrhines 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 (recall you learned about different color vision types in an earlier module). 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). 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. Platyrrhine Families and Subfamilies There are three families and six subfamilies of platyrrhines that you will be learning about over the next few pages. You can see the different families and subfamilies (end in "-inae") and how they are related to one another in the diagram below.
3.5 - 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 haplorrhine traits discussed below are considered derived traits. Cranial Traits 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. 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 (like your phone when you are texting). 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. Relative to strepsirrhines, we see many derived traits of the skull, including a fused frontal bone, fused mandibular symphysis, upper molars with hypocones in almost all taxa, and a deeper and more robust mandible for a more herbivorous diet. You can see images and more details of these differences here. Postcranial Traits Haplorrhines are generally larger than strepsirrhines, and so we see many more species that are folivorous and frugivorous, and fewer that are insectivorous (recall what you learned in the last module about body size and diet). 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. Ecology and Behavior The Haplorrhini differ from the Strepsirrhini in aspects of ecology and behavior as well. In addition to the dietary differences mentioned above, haplorrhines live in a wider range of habitat types and many more are terrestrial than what is seen in strepsirrhines. Haplorrhines also differ in social behavior. All but two haplorrhines live in groups, which is very different from the primarily solitary strepsirrhines. 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. Other Traits A couple of other interesting characters of the haplorrhini is that all members of our suborder are unable to synthesize vitamin C and instead must acquire it through our diet. Most mammals are able to synthesize vitamin C. Lastly, as mentioned earlier in this module, haplorrhines differ from strepsirrhines in female reproductive anatomy. Female haplorrhines have a simplex uterus (single cavity) and a hemochorial placenta (fewer layers between the mother and fetus).
