Animal Diversity Web

The Pri­mates are an an­cient and di­verse eu­ther­ian group, with around 233 liv­ing species placed in 13 fam­i­lies. Most dwell in trop­i­cal forests. The small­est liv­ing pri­mate is the pygmy mouse lemur, which weighs around 30 g. The largest is the go­rilla, weigh­ing up to around 175 kg.

Pri­mates ra­di­ated in ar­bo­real habi­tats, and many of the char­ac­ter­is­tics by which we rec­og­nize them today ( short­ened ros­trum and for­wardly di­rected or­bits, as­so­ci­ated with stereo­scopic vi­sion; rel­a­tively large brain­case; op­pos­able hal­lux and pollex; un­fused and highly mo­bile ra­dius and ulna in the fore­limb and tibia and fibula in the hind) prob­a­bly arose as adap­ta­tions for life in the trees or are prim­i­tive traits that were re­tained for the same rea­son. Sev­eral species, in­clud­ing our own, have left the trees for life on the ground; nev­er­the­less, we re­tain many of these fea­tures.

Pri­mates are usu­ally rec­og­nized based on a suite of prim­i­tive char­ac­ter­is­tics of the skull, teeth, and limbs. Some of these are listed above, in­clud­ing the sep­a­rate and well-de­vel­oped ra­dius and ulna in the fore­arm and tibia and fibula in the hind­leg. Oth­ers in­clude pen­tadactyl feet and pres­ence of a clav­i­cle. Ad­di­tional char­ac­ter­is­tics (not nec­es­sar­ily unique to pri­mates) in­clude first toe with a nail, while other dig­its bear ei­ther nails or claws, and stom­ach sim­ple in most forms (sac­cu­lated in some leaf-eat­ing cer­co­p­ithe­cids). Within pri­mates, there is a ten­dency to­wards re­duc­tion of the ol­fac­tory re­gion of the brain and ex­pan­sion of the cere­brum (es­pe­cially the cere­bral cor­tex), cor­re­lated with an in­creas­ing re­liance on sight and in­creas­ingly com­plex so­cial be­hav­ior.

The teeth of pri­mates vary con­sid­er­ably. The den­tal for­mula for the order is 0-2/1-2, 0-1/0-1, 2-4/2-4, 2-3/2-3 = 18-36. The in­cisors are es­pe­cially vari­able. In some forms, most in­cisors have been lost, al­though all re­tain at least 1 lower in­cisor. In oth­ers, the in­cisors are in­ter­me­di­ate in size and ap­pear to func­tion as pin­cers or nip­pers, as they com­monly do in other groups of mam­mals. In some, in­clud­ing most strep­sir­rhines (see next para­graph), the lower in­cisors form a tooth­comb used in groom­ing and per­haps for­ag­ing. In the aye-aye ( Dauben­toni­idae), the in­cisors are re­duced to 1 in each jaw and are ro­dent-like in form and func­tion. Ca­nines are usu­ally (but not al­ways) pre­sent; they vary in size, in­clud­ing within species be­tween males and fe­males. Pre­mo­lars are usu­ally bi­cus­pid (bilophodont), but some­times ca­nine-like or mo­lar-like. Mo­lars have 3-5 cusps, com­monly 4. A hypocone was added early in pri­mate his­tory, and the para­conid was lost, leav­ing both upper and lower teeth with a ba­si­cally quadrate pat­tern. Prim­i­tively, pri­mate mo­lars were brachy­dont and tu­ber­cu­lo­sec­to­r­ial, but they have be­come bun­odont and quadrate in a num­ber of mod­ern forms.

Liv­ing pri­mates are di­vided into two great groups, the Strep­sir­rhini and the Hap­l­or­rhini. Strep­sir­rhines have naked noses, lower in­cisors form­ing a tooth­comb, and no plate sep­a­rat­ing orbit from tem­po­ral fossa. The sec­ond digit on the hind foot of many strep­sir­rhines is mod­i­fied to form a " toi­let claw" used in groom­ing. Strep­sir­rhines in­clude mostly ar­bo­real species with many prim­i­tive char­ac­ter­is­tics, but at the same time, some ex­treme spe­cial­iza­tions for par­tic­u­lar modes of life. Hap­l­or­rhines are the so-called "higher" pri­mates, an an­thro­pocen­tric des­ig­na­tion if ever there was one. They have furry noses and a plate sep­a­rat­ing orbit from tem­po­ral fossa, and they lack a tooth­comb. Hap­l­or­rhines in­clude many more species, are more widely dis­trib­uted, and in most areas play a more im­por­tant eco­log­i­cal role. Hap­l­or­rhines are fur­ther di­vided into two major groups, the Platyrrhini and the Ca­tarrhini. Platyrrhines have flat noses, out­wardly di­rected nasal open­ings, 3 pre­mo­lars in upper and lower jaws, an­te­rior upper mo­lars with 3 or 4 major cusps, and are found only in the New World. Ca­tarrhines have paired down­wardly di­rected nasal open­ings, which are close to­gether; usu­ally 2 pre­mo­lars in each jaw, an­te­rior upper mo­lars with 4 cusps, and are found only in the Old World ( Cer­co­p­ithe­coidea, Homi­noidea).

Most pri­mate species live in the trop­ics or sub­trop­ics, al­though a few, most no­tably hu­mans, also in­habit tem­per­ate re­gions. Ex­cept for a few ter­res­trial species, pri­mates are ar­bo­real. Some species eat leaves or fruit; oth­ers are in­sec­tiv­o­rous or car­niv­o­rous.

Here, we fol­low An­der­son and Jones (1984) in for­mally di­vid­ing liv­ing pri­mates into two sub­or­ders, the Strep­sir­rhini and the Hap­l­or­rhini. We dif­fer, how­ever, in that we place hu­mans and their close rel­a­tives, the chim­panzee, go­rilla, and orang in the fam­ily Ho­minidae.

Tech­ni­cal char­ac­ters (strep­sir­rhines vs. hap­l­or­rhines)

Tech­ni­cal char­ac­ters (teeth)

Tech­ni­cal char­ac­ters (strep­sir­rhines)

Lit­er­a­ture and ref­er­ences cited

Feld­hamer, G. A., L. C. Drick­amer, S. H. Vessey, and J. F. Mer­ritt. 1999. Mam­mal­ogy. Adap­ta­tion, Di­ver­sity, and Ecol­ogy. WCB Mc­Graw-Hill, Boston. xii+563pp.

Thor­ing­ton, R. W., Jr., and S. An­der­son. 1984. Pri­mates. Pp. 187-217 in An­der­son, S. and J. K. Jones, Jr. (eds). Or­ders and Fam­i­lies of Re­cent Mam­mals of the World. John Wiley and Sons, N.Y. xii+686 pp.

Sav­age, R. J. G. and M. R. Long. 1986. Mam­mal Evo­lu­tion, an Il­lus­trated Guide. Facts of File Pub­li­ca­tions, New York. 259 pp.

Vaughan, T. A. 1986. Mam­mal­ogy. Third Edi­tion. Saun­ders Col­lege Pub­lish­ing, Fort Worth. vii+576 pp.

Vaughan, T. A., J. M. Ryan, N. J. Czaplewski. 2000. Mam­mal­ogy. Fourth Edi­tion. Saun­ders Col­lege Pub­lish­ing, Philadel­phia. vii+565pp.

Wil­son, D. E., and D. M. Reeder. 1993. Mam­mal Species of the World, A Tax­o­nomic and Ge­o­graphic Ref­er­ence. 2nd edi­tion. Smith­son­ian In­sti­tu­tion Press, Wash­ing­ton. xviii+1206 pp.

Click on the name of a fam­ily below to learn more:

Sub­or­der Strep­sir­rhini

• Fam­ily Lemuri­dae
• Fam­ily Cheirogalei­dae
• Fam­ily In­dri­idae
• Fam­ily Dauben­toni­idae
• Fam­ily Galag­o­nidae
• Fam­ily Lorisidae
• Fam­ily Lep­ile­muri­dae

Sub­or­der Hap­l­or­rhini

• Fam­ily Tar­si­idae
• Fam­ily Ce­bidae
• Fam­ily Cer­co­p­ithe­ci­dae
• Fam­ily Cal­litrichi­nae
• Fam­ily Hy­lo­bati­dae
• Fam­ily Ho­minidae

Con­trib­u­tors

Phil Myers (au­thor), Mu­seum of Zo­ol­ogy, Uni­ver­sity of Michi­gan-Ann Arbor.