Swindler 2002.5


26 27

Polydontia (extra teeth) are found in both extinct 
(Jungers and Gingerich, 1980) and extant  primate taxa 
(Colyer 1936; Krapp and Lampel, 1973; Lavelle and 
Moore, 1973; Miles and Grigson, 1990; Schultz, 1935).  
But as Jungers and Gingerich (1980:1) mentioned in 
their investigation, “the developmental basis of extra 
teeth in a particular tooth category remains obscure.”  
Several explanations have been proffered through the 
years regarding the development of fourth molars, e.g., 
distal growth of the dental lamina, duplication of the M3 
tooth germ and atavism (see in particular Jungers and 
Gingerich, 1980; Miles and Grigson, 1990).  The fourth 
molar is a rarity in the genus Macaca.  In an ongoing 
longitudinal study of dental development in Macaca 
nemestrina

, 
M

4
 and M4 were observed radiographically 

in a male specimen. Development of the M4 is discussed 
and the appearance and frequency of M4’s in the 
Anthropoidea is reviewed.

MATERIALS AND METHODS

The parental generation was collected from free-
ranging populations in Sumatra and transported to the 
National Primate Research Center at the University of 
Washington.  These animals were the breeding colony of 
the animals in the longitudinal growth and development 
study (Sirianni and Swindler, 1985).  After weaning, 
between 3 and 8 months, the animals were raised and 
housed separately with their age mates.  Radiographs 
of the head in norma lateralis were taken on a regular 
schedule from about three months to seven years.  There 
were a total of 140 animals in the study, 70 females and 
70 males.  Tables 1, 2 and 3 present the number of 
specimens with M4’s except for the figures presented 
of Selenka (1898), Hrdli�ka (1907) and Hooijer (1948) in 
Table 2 that record the total number of M4’s 

RESULTS AND DISCUSSION

The M4 was observed in the radiograph of one male 
and was present in both the maxilla and mandible. Thus 
of a total sample of 140 Macaca nemestrina 0.7% showed 
this condition (Table 1).  A slightly lower percentage 
has been reported for the presence of M4 for the genus 
Macaca by Miles and Grigson, 0.2% of 901 animals (1990), 
Lavelle and Moore (1973) recorded 0.3% for 350 Macaca 

ABSTRACT  Fourth molars are not common in the 
anthropoidea.  Orangutans possess the highest frequen-
cies (7-13%) while many genera in the suborder lack 
the fourth molars. A review of the incidence of M4’s in 

Daris R. Swindler
Department of Anthropology, University of Washington, Seattle, WA 98195 U.S.A

Fourth Molars in the Anthropoidea

Daris R. Swindler, Department of Anthropology, 
University of Washington, Seattle, WA 98195 U.S.A.  
E-mail:  dswindle@u.washington.edu

TABLE 1.  Incidence of M4’s in the Cercopithecidae

  Number of
 Genus Specimens M4 Percent

Colobus1 1,485 22 4.00
Colobus2 140 0 0.00
Colobus8 155 5 3.23
Presbytis1* 289 1 0.30
Presbytis2 100 0 0.00
Presbytis8 321 1 0.31
Pygathrix1 16 0 0.00
Rhinopithecus1 17 0 0.00
Rhinopithecus3 11 1 9.10
Simias1 10 0 0.00
Nasalis1 83 0 0.00
Cercopithecus1 1,823 10 0.50
Cercopithecus2 350 4 1.10
Cercopithecus8 2,460 16 0.65
Erythropithecus1 95 3 3.20
Erythropithecus8 95 2 2.11
Cercocebus1 311 0 0.00
Papio1 410 2 0.50
Papio2 38 1 2.60
Papio8 541 6 1.11
Mandrillus1 56 0 0.00
Theropithecus1 7 0 0.00
Macaca1 901 2 0.20
Macaca4 140 1 0.70
Macaca2 350 1 0.30
Macaca8 2,379 9 0.38

1Miles and Grigson (1990) (M4 and M
4
)

2Lavelle and Moore (1973) (M4 and M
4
)

3Hooijer(1952) (M4)
4This paper (M4 and M

4
)

8Krapp and Lampel (1973) (M4 and M
4
)

*P. entellus and vetulus groups

the Anthropoidea is presented and a description of the 
ontogeny of M4 in Macaca nemestrina is described and 
offered as an explanation of the development of M4’s in 
this taxon.



26 27

Fig. 2.  Macaca nemestrina 7.0 years old. M
4 

crown 
complete and initial emergence has begun.  There 
appears to be initial mineralization of M4 within a 
crypt.

Fig. 1.  Macaca nemestrina 6.2 years old. M
4
 crown visible 

within its crypt distal to M
3
.  An interdental bony 

septum separates M
4
 from M

3
.

FOURTH MOLARS

1, 2 and 3).  Gibbons appear to lack  development of M4, 
a fact that has been known since the work of Bateson 
(1894) as reported in Miles and Grigson (1990). Also, 
several different genera of both New and Old World 
monkeys lack the 0ccurrence of M4.  The taxonomic 
presence of M4’s in the living Anthropoidea seems to 
lack any discernible correlation with body mass or facial 
prognathism since the M4 condition appears in primates 
ranging in size from gorillas to squirrel monkeys and in 
primates with  both long and short snouts.

The aetiology of polydontia is uncertain.  Earlier 
literature suggested that such occurrences were the 
result of atavism, although today the term has lost favor 
in most scientific circles.  The heritability of the condition 
is not completely understood (Finn, 1967); however, 
there is evidence indicating that polydontia appears 
more often in isolated populations, and especially 
among some domesticates, which has suggested thethe 
involvement of genetic drift as a possible cause to Miles 
and Grigson (1990).
“Connate teeth” is an anomaly; that is, double teeth, 
incomplete dichotomy, or syndonty that should be 
reserved for teeth that are “developed or born together” 
(Miles and Grigson, 1990; Winkler and Swindler, 1993; 
Drusini and Swindler, 1994).

In the present case, both the upper and lower M4 
would seem to represent the continued distal growth 
of the dental lamina in that M4 appears distally to 
the formation of M3. The development of M

4
 will be 

discussed since it is more easily observed and it is 
assumed that M4 passed through similar developmental 
stages.  The dental follicle and M

4
 appear between 5.5 

and 6.2 years.  At 6.2 years the crown is present, the 
cusps are connected but the crown is not complete 
and it is inclined obliquely at about 450 to the occlusal 
plane (Fig. 1).  There is no root development and the 
cleft has not yet formed, and as seen in this radiograph, 
an interdental septum separates M

3
 and M

4
 (Fig.1).  In 

Fig. 2, (7.0 years), the crown appears nearly formed 
with beginning root formation while the crown is still 
inclined relative to the occlusal plane.  The mesiodistal 
length of the crown is 8.5 mm which is about 3 mm 
shorter that the average size of M

3
 in male M. nemestrina 

(10.9 mm) and about equal in length to M
2
 (8.6 mm) 

(Swindler, 2002).  Thus, this M
4
 is within the normal 

mesiodistal size range for molars of M. nemestrina. 
Unfortunately, this animal was not studied after 7 years 
of age so there is no information regarding the age of the 
animal when M

4
 emerged.

CONCLUSION

The presence of M4’s is rare among living primates, 
particularly in gibbons, New World monkeys and 
colobine genera.  The orangutans possess the highest 
frequency of M4’s (7 to 13%) of all living anthropoidea.  
The aetiology of M4’s remains uncertain and may 
represent different developmental processes in different 

as having total polygenesis but did not designate which 
teeth were involved.  Krapp and Lampel (1973), in their 
comprehensive study of dental anomalies of living 
anthropoidea, found 0.38% of 2,379 macaque specimens 
with fourth molars.

The presence of extra teeth is low in all living 
cercopithecids irrespective of the tooth group, and 
it is interesting to note that most investigations have 
found a higher incidence of M4’s in the subfamily 
Cercopithecinae than in the Colobinae,   (Table 1).  A 
notable exception to this finding is the 9.1% presence 
in Rhinopithecus; however, that figure represents one 
specimen out of a total of only eleven animals (Table 
1).  Of all the genera depicted in Tables 1, 2 and 3, 
Pongo has the highest frequency of M4 while colobines 
and New World monkeys generally have the lowest 
frequencies.  Among living primates, Pongo is generally 
reported to have the highest percentage of M4’s (Tables 



28 29

species.  On the basis of the present specimen, it seems 
clear that M

4
 develops in a normal manner i.e., follicle, 

initial calcification, crown formation and root formation 
from a distal extension of the dental lamina, and that 
tooth formation takes place in a follicle distal to an 
interdental septum between it and M

3
.

REFERENCES CITED

Bateson W.  1894.  Materials for the Study of Variation. 
London: Macmillian.

Colyer JF.  1936.  Variations and diseases of the teeth of 
animals. London: John Bale, Sons & Danielsson.

Drusini AG, Swindler DR.  1994,  Connate incisors in a 
Pre-Columbian mandible from Nasca, Peru.  Dental 
Anthropology Newsletter 9:11.

Hooijer DA. 1948.  Prehistoric teeth of man and the 
orang-utan from central Sumatra, with notes on the 
fossil orang-utan from Java and southern China. 
Zoologische Mededeelingen Museum, Leiden, 29:
175-301.

Hooijer DA.  1952.  Notes on the dentition of the golden 
monkey Rhinopithecus.  J. Mammology 33:258-260.

Hrdlička  A.  1907.  Anatomical observations on a 

TABLE 2.  Incidence of M’s in the Pongidae
 and Hylobatidae

 Number of
 Genus Specimens M4 Percent

Gorilla1 546 22 4.00
Gorrila2 190 12 6.30
Gorilla8 1,409 56 4.00
Pan1 467 13 2.40
Pan2 100 2 2.00
Pan8 1,040 28 2.72
Pongo1 229 16 7.00
Pongo2 100 6 6.00
Pongo5 88 6 6.80
Pongo6 388 46 11.90
Pongo7 44 6 13.60
Pongo8 1,808 200 11.12
Hylobates1 * 391 3 0.80
Hylobates2 150 0 0.00
Hylobates8 1,276 9 0.71

1Miles and Grigson  (1990) (M4 and M
4
)

2Lavelle, and Moore (1973) (M4 and M
4
)

5Hooijer (1948) (M
4
)

6Selenka (1898) (M
4
)

7Hrdlička (1907) (M
4
)

8Krapp and Lampel (1973) (M4 and M
4
)

*Hylobates and Symphalangus

TABLE 3. Incidence of M’s in the Cebidae

  Number of
 Genus Specimens M4 Percent

Lagothrix1 94 0 0.00
Brachyteles1 25 0 0.00
Ateles1 232 7 3.00
Ateles8 612 6 0.98
Saimiri1 110 1 0.90
Saimiri8 100 1 0.10
Cebus1 651 4 0.60
Alouatta1 787 3 0.40
Alouatta8 956 3 0.31
Cacajao1 23 0 0.00
Pithecia1 155 0 0.00
Callicebus1 122 0 0.00
Aotus1 10 0 0.00

1Miles and Grigson (1990) (M4 and M
4
) 

8Krapp and Lampel (1973) (M4 and M
4
)

collection of orang skulls from Western Borneo.  
Proc US Natl Mus 31:539-568

Jungers LJ, Gingerich PD.  1980.  Supernumerary molars 
in Anthropoidea, Adapidae, and Archaeolemur: 
Implications for primate homologies.  Am J Phys 
Anthropol 52:1-5.

Krapp F, Lampel G.  1973.  Zahnanomalien bei 
Altweltaffen (Catarrhina). Rev suisse Zool 80:83-
150.

Lavelle CLB, Moore WL. 1973.  The incidence of agenesis 
and polygenesis in the primate dentition.  Am J Phys 
Anthropol 38:671-680.

Miles AEW, Grigson C. 1990.  Colyer’s variations 
and diseases of the teeth of animals. Cambridge: 
Cambridge University Press. 

Schultz AH. 1936.  The eruption and decay of the 
permanent teeth in primates.  Am J Phys Anthropol 
19:489-581. 

Selenka E.  1898.  Rassen, Schadel und Bezahnung 
des Orangutan. Menschenaffen (Anthropomorphae). 
Studien uber Entwicklung und Schadelbau. 
Wiesbaden: CW Kreidels Verlag.

Sirianni JE, Swindler DR. 1985.  Growth and 
development of the pigtailed macaque. Boca Raton: 
CRC Press, Inc.

Swindler, DR. 2002.  Primate dentition:  an introduction 
to the teeth of non-human primates. Cambridge: 
Cambridge University Press. 

Winkler LA, Swindler DR. 1993.  Report:  Presence of 
a connate tooth in a neonate chimpanzee.  Dental 
Anthropology Newsletter 8:9.

FOURTH MOLARS