primate taxonomy

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Primate Taxonomy

Introduction

This first lecture is designed to introduce the primate order in terms of its classification and tofamiliarise you with the animals so that the rest of the course makes some sort of sense. I willcover a working definition of what makes a primate, give you a general classificationscheme, describe the major features that identify the groups within the classification and

discuss some of the controversial areas of the classification. I shall treat the taxonomy as asynonym for classification which seems to be its commonest current usage, although youshould be aware that some people consider taxonomy to be more about the principles behindthe classification than the classification itself.

Definition of a primate

Most primatology textbooks include a definition of a primate in their introductory chapters.This discussion comes from Martin [Martin, 1986] and is as good a starting point as any.

Mivart's Definition

Like many definitions, the definition of what makes a primate (as opposed to a rodent, or acarnivore etc.) is complex. There is little argument as to the core groups of animals today thatare primates as I will be illustrating later, but as one goes back in the fossil record, there is

more dissension. Still, a purely descriptive definition is needed as a starting point and Mivart[Mivart, 1873] provided this in figure 1.

Figure 1. Mivart’s definition of a primate [Mivart, 1873]

Mivart’s Primate Definition

Unguiculate, claviculate, placental mammals, with orbits encircled by bone; three kinds ofteeth, at least at one time of life; brain always with a posterior lobe and calcarine fissure; theinnermost digit of at least one pair of extremities opposable; hallux with a flat nail or none; awell developed caecum; penis pendulous; testes scrotal; always two pectoral mammae.

Notes:

Unguiculate - possessing nails, hooves or claws

Claviculate - possessing a clavicle (collar bone)

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Le Gros Clark's Definition

Mivart’s definition is quite a good definition considering its age and certainly has the valueof being nice and short. A rather more up to date version was produced by Le Gros Clark [LeGros Clark, 1959] (see figure 2).

Figure 2.Le Gros Clark’s definition of a primate [Le Gros Clark, 1959]

Le Gros Clark’s Definition

1. Preservation of generalised limb structure with primitive pentadactyly.

2. Enhancement of free mobility of the digits, especially of the pollux and hallux (both usedfor grasping).

3. Replacement of sharp, compressed claws by flat nails; development of very sensitivetactile pads on the digits.

4. Progressive shortening of the snout.

5. Elaboration of the visual apparatus, with the development of varying degrees of binocularvision. Orbits ringed with bone.

6. Reduction of the olfactory apparatus.

7. Loss of certain elements of the primitive mammalian dentition. Preservation of a simplemolar cusp pattern.

8. Progressive expansion and elaboration of the brain, especially of the cerebral cortex.

9. Progressive and increasingly efficient development of gestational processes.

Considering each of these features in turn:

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Preservation of generalised limb structure with primitive pentadactyly

Figure 3. Diagram of the forelimb of a variety of tetrapods showing how the primate hasretained the primitive pentadactyly limb (3 girdle bones; 1 upper limb bone; 2 lower limbbones; carpals/tarsals; meta-carpals/tarsals; phalanges) whereas various other mammalianorders have lost various bones (taken from Strickberger [Strickberger, 1990]).

As you can see from figure 3 the primates have retained a limb bone structure that is verysimilar to that of the primitive tetrapod, whereas the other mammals shown have considera-

bly reduced bone numbers.

Enhancement of free mobility of the digits, especially of the pollux and hallux (both used forgrasping)

Figure 3 also shows how the primate hand and foot has long, mobile digits compared to someother mammals. Coupled with this, primates can use a variety of power and precision grips tomanipulate objects. Figure 4 shows a variety of primate autopodia. Loss of grasping capabil-ity in the foot is a feature peculiar to humans.

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Figure 4. Photographs of the autopodia (hands and feet) of a variety of primates. Top left,hand of Pithecia pithecia (white-faced saki); top right, foot of Lemur catta (ring-tailedlemur); bottom left, foot of Pan troglodytes (common chimpanzee); bottom right, foot ofCercopithecus hamlyni (Hamlyn’s owl monkey).

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Replacement of sharp, compressed claws by flat nails; development of very sensitive tactilepads on the digits

Figure 5. Photograph of a variety of primate hands showing the presence of flattened nailsand sensitive dermatoglyphs. Top right, Trachypithecus obscura (dusky leaf monkey); topleft, Callithrix geoffroyi (Geoffroy’s marmoset); bottom left, Pan troglodytes (common

chimpanzee); bottom right Sanguinus oedipus (cotton-top tamarin). The two photographs onthe right hand side are of Callitrichidae which are the exceptions to the normal primate ruleand have claws rather than nails on most of their fingers.

Figure 5 shows a examples of the flattened nails that are characteristic of primate digits andat the same time shows that rules are always made to be broken since in some primates thenail has reverted to being a claw.

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Progressive shortening of the snout

Figure 6. Photographs of a selection of mammalian skulls. Top left, Ursus arctos (brownbear); top right, Pan troglodytes (common chimpanzee); bottom left, Macropus giganteus

(grey kangaroo); bottom right Daubentonia madagascariensis (aye-aye) (Photos fromDorling-Kindersley [Dorling-Kindersley, 1994] and Alexander [Alexander, 1994]).

Figure 6 shows a selection of mammalian skulls. The primate skulls are the two on the rightand as you can see, they have relatively short snouts. Obviously there is a huge amount of

variation in gross skull shape across the mammalian class, but certainly, on average, primateskulls tend to be short.

Elaboration of the visual apparatus, with the development of varying degrees of binocularvision. Orbits ringed with bone.

Figure 6 also shows the characteristic morphology of the primate orbit. The eyes face for-ward for binoccular region, the eyes tend to be quite large, and the orbit is either a fullyenclosed cup (as in the chimp in figure 6) or a lateral post-orbital bar (as in the aye-aye). Inmost other mammals (for example the bear and kangaroo), the eye is simply plastered ontothe side of the skull and held in place by soft tissue.

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Reduction of the olfactory apparatus

The reduction in the size of the snout and the increased reliance on vision has also led to arelative reduction in the olfactory apparatus compared to many other mammals. This is againapparent from figure 6 and is associated with the reduction in size of the snout.

Loss of certain elements of the primitive mammalian dentition. Preservation of a simple

molar cusp pattern.

Figure 7. Diagram of the teeth of the upper jaws of a selection of mammals (diagrams fromHillson [Hillson, 1986]).

As you can see from figure 7, primates (as indeed do most mammals – teeth are often usedfor identification) have a fairly distinctive dentition. Primitive mammals are thought to havehad a dental formula of 3 1 4 3

3 1 4 3

. . .

. . . which means that they had 3 incisors, 1 canine, 4 premolars and

3 molars in each half of their upper jaw and the same in each half of their lower jaw. Modernmammals have a variety of dental formulas, but the typical dental formulas for primates are2 1 3 3

2 1 3 3

. . .

. . . and 2 1 2 3

2 1 2 3

. . .

. . .. The shape of the teeth is also diagnostic although there is quite a lot of variation

between different species.

Progressive expansion and elaboration of the brain, especially of the cerebral cortex

Primates of all types have larger brains that would be expected of mammals of their size(brain size is strongly correlated with body size, so any comparative measure of brain size

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has to take this into account). The cerebral cortex is the anterior part of the brain that seemsto be mainly involved in higher cognitive processes such as memory and language. You cansee the increase in brain size by looking at the sizes of the cranium in figure 6 and figure 8shows a graph of brain size against body size for a variety of animals.

Figure 8. Graph showing the relationship between brain and body size for a variety of ani-

mals. Note that the scales are logarithmic (Graph from Dunbar [Dunbar, 1996]).

Progressive and increasingly efficient development of gestational processes

Mammals are generally characterised by specialised gestational mechanisms that lead to thebirth of live offspring. This process is brought about by means of the implanatation of theembryo into the wall of the uterus and in eutherian mammals the development of a chorio-allantoic placenta to allow nutrient and waste transfer between the embryo and the mother[Hamilton et al., 1947]. The structure of the placenta is complex, but it basically consists of aseries of membranous barriers between the maternal and embryonic blood supplies. The twoblood supplies never mix and chemical transfer is by diffusion. In some mammals, includingprimates, a number of these membranes have disappeared leading to a reduction in diffusionbarriers and more efficient transfer across the placenta.

Napier and Napier's Defintion

Napier and Napier [Napier and Napier, 1967] have added two extra items to this list (see

figure 1).

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Figure 9. Napier and Napier’s definition of a primate.

Napier and Napier’s Definition

Le Gros Clark’s definition plus:

10. Prolongation of postnatal life periods.

11. Progressive development of truncal uprightness leading to a facultative bipedalism.

Prolongation of postnatal life periods

Primates as a group tend to have long periods of postnatal care. Offspring remain dependenton their parents for long periods allowing opportunities for social learning and requiring large

amounts of parental investment. For the ecologists among you, primates tend to be K-selectedrather than r-selected.

Figure 10. Photograph of a family group of yellow baboons (Papio hamadryas cyanocepha-

lus) [Rowe, 1996].

Progressive development of truncal uprightness leading to a facultative bipedalism

This refers to the suggestion that primates tend to adopt postures with the trunk held verti-cally and that a number of primates are able to walk bipedally when necessary. Facultative

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bipedalism – the ability to walk on two legs when required – is found in the apes and isoccasionally seen in other primates. Habitual bipedalism – walking on two legs all the time –is only found in humans and their immediate ancestors.

Figure 11. Photographs of two primates walking bipedally: left, Pongo pygmaeus (orang-utan); right Pan paniscus (pygmy chimpanzee) [Rowe, 1996].

At first view, these various definitions seems OK (apart from the dreadful language whichmakes the whole thing read like a life insurance document), but if fact there are problems

with them:

Firstly, there is no unique characteristic that defines a primate. It is a list of shared character-istics and trends – most of which are not even derived, but are retentions of ancestral featureswhich is definitely not good. Many mammalian orders can be characterised by a singleanatomical feature that they uniquely possess such as wings for bats which makes classifica-tion much easier.

Secondly, many of these features are behavioural or depend on soft tissue anatomy. They willnot help us identify a fossil primate.

Thirdly, many of these features are not really features of primates in general but trends thatrun through the order as the primates get more and more human-like. These are not necessar-ily very useful in an individual case.

Fourthly, there are many primates that do not have all the features listed. Indeed, there is nofeature that all primates share. This is a set of features that you would use as evidence. Aprimate is likely to show many of these features, but we cannot a priori say which ones.

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Thus it can be very difficult, especially when dealing with very early mammals and frag-mentary fossils, to decide whether a specimen is a primate or not. There are even wholegroups (extant ones such as the tree shrews and extinct ones such as plesiadapids) that somepeople classify as primates whilst others do not. Similarly, there are several mammaliangroups (insectivores, bats, flying lemurs) that have been considered the closest living rela-

tives to primates and the jury is certainly still out on this question.

Primate Classification

Classification serves two distinct purposes. Firstly it is there so we all know which animalswe are talking about when we are discussing them – whether this is for scientific use injournals, knowing which shelf to look on in a museum or setting laws for the transport of liveanimals across national boundaries. Secondly, it should not be an arbitrary grouping butshould reflect the evolutionary relationships of the animals. In theory these two uses shouldnot interfere with each other but in practice we do not accurately know the evolutionaryrelationships among the primates so a classification based entirely on current consensusthinking of evolutionary relationships would change on a monthly basis as the next scientificpaper on the subject came out. This means that we have a fairly well established classifica-

tion for the primates that changes relatively slowly that only approximately relates to currentthinking on evolutionary relationships. Even so, you will find several different classificationschemes in use in textbooks.

The classification scheme I shall adopt for this course is the one from Szalay and Delson[Szalay and Delson, 1979] (reprinted in the back of Conroy [Conroy, 1990]). It is probablynot the most commonly used scheme, but I feel it reflects the anatomy quite well. Thescheme in Fleagle [Fleagle, 1999] is the one more generally encountered and I will periodi-cally comment on the differences.

Before we go on, a note on typography1. The way that taxonomic terms are written in impor-tant (translation: you will lose marks if you get it wrong!). Species names are written initalics with the name of the genus starting with a capital (uppercase) letter and the name of

the species starting with a lowercase letter such as Varecia variegata. Further subspeciesdesignations are added after this (also in italics) such as Varecia variegata rubra. After thefirst usage in an essay or paper, the genus name can be abbreviated to its first letter (still incapitals) such as V. variegata. Within the primate order, the species names are all unique sothere should be no chance of confusion. Common names of animals do not have capitalletters (red ruffed lemur in this case). When referring to a whole genus, the genus name isused on its own, with a captial letter and in italics (Varecia). Higher taxonomic levels (sub-families, families, superfamilies, infraorders and suborders) usually have two forms: a

1 In practice, typographical rules are rarely carved in stone. Books and journals have a ‘house style’ which

tightly defines the typographic rules they use. The recommendations here are widely followed but you willencounter differences.

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latinised form and an anglicised form. The latinised form is probably the correct form butthese names are such a mouthful that the anglicised names are generally more commonlyused. Italics are not used, and only the latinised form has a capital letter. Most people wouldput Varecia in the family Lemuridae, the superfamily Lemuroidea, the infraorder Lemuri-formes, and the suborder Strepsirhini (and upwards: the order Primates, class Mammalia,

Phylum Chordata, kingdom Metazoa, superkingdom Eukaryotes). The anglicised versions arethus: lemurid, lemuroid, lemuriform and strepsirhine. There are other levels in the hierachythat can optionally be used. Subfamily is probably the commonest –- it is not used in ourreference classification for Varecia (although you could make use Lemurinae) but, forexample, humans are in the subfamily Hominae, anglicised name hominin. All the varioustaxonomic levels can have a name and a date written after them to denote the person whofirst used that particular name but unless you are writing a taxonomic textbook (when it isvery useful), it is probably not worth doing this. Note that the taxonomic level of a term canusually be identified by the ending of the word. Thus subfamilies end in inae (in), familiesend in idea (id), superfamilies end in oidea (oid). Unfortunately, the other taxonomic levelsare less consistent, but if your etymological taste buds have been tickled the you might want

to check out Gotch [Gotch, 1995] for a highly detailed discussion.

Suborders

Table 1. The primate suborders

Order Primates

Suborder Strepsirhini Haplorhini

The first major split in the primate order is between the Strepsirhini and the Haplorhini (seetable 1). Unfortunately, this is also the first (and probably most important) difference of

opinion between the various classification schemes. Fleagle [Fleagle, 1999] uses Prosimiiand Anthropoidea as his first major split and you will hear and read the terms prosimian andanthropoid all over the place. I will certainly talk about prosimians a lot – mostly because it ismuch easier to say than strepsirhines and is much more widely used. Unfortunately strep-sirhine is not synonymous with prosimian and haplorhine is not synonymous with anthropoidalthough in many instances the difference is irrelevant. The difficulty lies in a rather special-ised and rather small infraorder called the Tarsiiformes which are classified as prosimian onthe one hand and haplorhine on the other (as shown in table 2). What this means in practice isthat you should use the strepsirhine/haplorhine distinction formally, but its OK to use theprosimian/anthropoid terms in less formal settings provided you are not talking about tarsi-ers! The other occasion when the term prosimian is quite useful is that because it is rather

less precise in its anatomical definition, we can be fairly sure that early fossil primates fallinto the prosimian category but there is a certain amount of uncertainty about whether some

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of them are haplorhine or strepsirhine. Mind you, this is not necessarily a good thing. Woollyclassification is not terribly helpful.

Table 2. Comparison of the two common primate suborder classifications

Order Primates


Suborder Prosimii Anthropoidea

Infraorder Tarsiiformes

The other thing to note when reading about strepsirhines and haplorhines is that strepsirhinesare often referred to as ‘primitive’. This is a valid term when talking about fossil forms and isfine when talking about particular traits (where it means a trait that is found in an ancestral

form which has been retained in a current form). It is not a particularly useful term to applyto a whole animal. What people generally mean when they talk about ‘primitive’ and ‘ad-vanced’ extant primates is less or more like humans and that is an incorrect usage. Humansdo indeed have some advanced features (features not found in their ancestors) such as largebrains and feet adapted to habitual bipedalism, but then all extant species tend to have a fewspecialised features that set them apart from other species (specialised throat anatomy toallow extremely loud vocalisations in Indri, multi-chambered stomachs for leaf fermentationin Colobus to name but a few). To describe an animal as a whole as advanced requires somesort of subjective value judgement on some non-specific notion of importance of theirspecialised traits and it generally all boils down to, “if it's a feature that humans are proud ofthen it’s advanced”.

Infraorders

Table 3. The primate infraorders

Order Primates


Infraorder Lemuriformes Tarsiiformes Platyrrhini Catarrhini

The next taxonomic level is infraorder (see table 3). This lumps all the extant strepsirhinesinto a single infraorder, the lemuriforms. There are other strepsirhine suborders in the classi-fication but they only contain fossil forms so we will not cover them in this section. Theyhave truly frightening names and the stability of the fossil classification is rather poor.

Tarsiiforms only contain the tarsiers which small, nocturnal primates with a very restrictedgeographical range in Southeast Asia although there are some important fossil members of

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this group. Platyrrhines and catarrhines (note the double r as opposed to the single r instrepsirhine and haplorhine) consist of the true monkeys, apes and humans and split neatly ongeographic lines. The platyrrhines are confined exclusively to South and Central America(the New World) and catarrhines, with the exception of humans who get everywhere, live inAfrica and Asia2. Thus platyrrhines are known as New World Monkeys (NWM) since they

are all monkeys found in the Americas. Catarrhines consist of Old World Monkeys (OWM:monkeys found in Asia and Africa), Apes and Humans.

Geography is extremely important in classification. Because speciation is generally associ-ated with geographical isolation followed by diversification, different groups of animals tendto occur in geographically isolated units. An example of this is Madagascar [Garbutt, 1999].This island off the East coast of Africa actually broke away from the Indian subcontinent anddrifted southwards. It has almost certainly never been connected to Africa by any land bridgeand has been isolated from India for 80 million years. The assumption is that it was colonisedby primates due to extremely rare rafting episodes where small numbers of early primateswere accidentally washed from the East African shore to Madagascar clinging to pieces offloating vegetation. This is a highly unlikely process but we think it probably occurred twice

in Madagascar's early history since there are two quite different primate groups now foundthere. A somewhat similar story may also have happened in South America since it also has ahighly specific mammalian fauna and was isolated from North America when primates firstappeared on the continent. Unfortunately it is slightly less convincing in this case – a 400 kmrafting feat seems reasonably feasible whereas a 2000 km journey from Africa seems un-likely (600 km is the longest rafting journey where we have reasonable evidence that itoccurred [Conroy, 1990]). The alternative suggestion is that the primates ‘island hopped’through the Caribbean from North America which had large primate populations at the time[McKenna, 1980].

Superfamilies

Table 4. The primate superfamilies

Order Primates

Suborde Strepsirhini Haplorhini

Infraorder Lemuriformes Tarsiiformes Platyrrhini Catarrhini

Superfamily Lemuroidea Lorisoidea Tarsioidea Ceboidea Cercopithecoidea Hominoidea

Table 4 shows the superfamily divisions. Because Tarsiiformes and Platyrrhini only contain asingle superfamily (in most classification schemes) even when the fossil forms are consid-ered, you are unlikely to see these terms used. Lemuroids are geographically restricted to the

island of Madagascar and consist of the large-bodied, diurnal lemurs. Lorisoids are more

2 Primate fossil forms of all primates are more widespread being found in North America and Europe as well.

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widespread consisting of the small-bodied, nocturnal primates found in Madagascar, Africaand Asia. Some classification schemes (for example Simons [Simons, 1972]) put all theMalagasy strepsirhines into Lemuroidea arguing that Madagascar was actually colonised by asingle rafting event and there is certainly dispute in this area (see Conroy [Conroy, 1990] fordiscussion). The cercopithecoids correspond to the Old World Monkeys and the hominoids

are apes and humans.

Families

Table 5. The primate families.

Order Primates


Infraorder Lemuriformes Tarsii-formes

Platyrrhini Catarrhini

Superfa-mily

Lemuroidea Lorisoidea Tarsi-oidea

Ceboidea Cerco-pithec-

oidea

Homin-oidea

Family Lemur-

idae

Indri-

idae

Daub-

entoni-

idae

Cheiro-

galeidae

Lorisidae Tarsiidae Cebidae Atelidae Cerco-

pithec-

idae

Homin-

idae

Once we get to the family level (see table 5) there starts to be a great deal of disagreementbetween various taxonomists. I'll stick with Szalay and Delson [Szalay and Delson, 1979] forthe simple reason that they have relatively few families and that makes it a little easier tolearn but you will find that family level classification varies from paper to paper. Lemuridscomprise the typical lemur forms (with lemur in their common name) except for the woolylemurs which are in the Indriids along with indries and sifakas. Daubentoniidae has a singleextant member: the very peculiar aye-aye which is so utterly strange that it was classified as a

rodent for many years. Lorisids include the slow moving, tail-less lorises, the much moreacrobatic bushbabies and the dwarf lemurs. Cebids include the smaller bodied New WorldMonkeys (capuchins, squirrel monkeys, marmosets and tamarins). The larger bodied SouthAmerican monkeys (spider and howler monkeys, sakis and uakaris) and the only nocturnalmonkey (the aptly named night monkey) are all Atelids. All extant old world monkeys(guenons, baboons, macaques and leaf monkeys) are cercopithecoids, and in this classifica-tion, apes and humans share the hominid family. This latter grouping sits quite happily withprimatologists who have long known that humans are just naked apes but anthropologists (avery influential bunch) always want to distance humans from non-human primates (NHP)and tend to reserve Hominidae for humans and fossil forms after the split from the great apes.They use another family, Pongidae, specifically for the great apes. Taxonomically this is

certainly a bad idea (especially given the recent molecular evidence), but many people find itpolitically more acceptable and you will certainly find the name pongid commonly used inthe literature.

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Here are some examples from these families (all taken from Rowe’s excellent book [Rowe,1996]).

Figure 17. Black and white ruffed lemur, Varecia variegata.

Figure 18. Indri, Indri indri.

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Figure 19. Aye-aye, Daubentonia madagascariensis.

Figure 20. Coquerel’s dwarf lemur, Microcebus coquereli.

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Figure 21. Slender loris, Loris tardigradus.

Figure 22. Philippine tarsier, Tarsius syrichta.

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Figure 23. Buffy headed marmoset, Callithrix flaviceps.

Figure 24. Black and gold howler monkey, Alouatta caraya.

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Figure 25. Diana monkey, Cercopithecus diana.

Figure 26. Orang-utan, Pongo pygmaeus.

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Bibliography

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Dorling-Kindersley. Ultimate Visual Dictionary. London: BCA, 1994.

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Garbutt, N. Mammals of Madagascar. Sussex: Pica Press, 1999.

Gotch, A.F. Latin Names Explained. London: Cassel, 1995.

Hamilton, W.J., J.D. Boyd, and H.W. Mossman. Human Embryology (Prenatal Development

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Martin, R.D. “Primates: a Definition.” In Major topics in primate and human evolution, eds.B. Wood, L. Martin, and P. Andrews. 1-31. Cambridge University Press: Cambridge, 1986.

McKenna, M. Early History and Biogeography of South America's Extinct Land Mammals.New York: Plenum, 1980.

Mivart, S.G. “On Lepilemur and Cheirogaleus, and on the Zoological Rank of the Lemuroi-dea.” Proceedings of the Zoological Society of London (1873): 484-510.

Napier, J.R., and P.H. Napier. A Handbook of Living Primates. London: Academic Press,1967.

Rowe, N. The Pictorial Guide to Living Primates. New York: Pogonias Press, 1996.

Simons, E. Primate Evolution. New York: Macmillan, 1972.

Strickberger, M.W. Evolution. Boston: Jones and Bartlett, 1990.

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