The circumnatal status of molar crown maturation among the hominoidea

Archr or01Biol. Vol. 14,pp. 639-659,1969.PcrgamonPress. Printedin Gt. Britain.

THE CIRCUMNATAL STATUS OF MOLAR CROWN MATURATION AMONG THE HOMINOIDEA S.

University

of Pittsburgh,

W.

Cleft

OKA

and

B. S.

Palate Research 15213, U.S.A.

KRAUS

Center,

Pittsburgh,

Pennsylvania

Summary-The permanent first molars of the Pongidae, Hylobatidae and Hominidae are compared at the circumnatal and the eruptive stages. The calcification of the cusps of these molars at the time of birth is similar in all of the species with the exception of the gibbon which is advanced. The M1 of the pongids and man have three cusps calcified at the time of birth. They are the protoconid, metaconid, and the hypoconid, and the sequence of calcification follows this order. The entoconid on the orangutan Mi bud is calcified on the tip. The entoconid of the gibbon Mi is also calcified, but to a greater extent, and the mesial cusps have a calcified bridge between them. The M’ has three cusps calcified at the time of birth. The paracone, protocone and metacone are calcified in this sequence. The gibbon has all four cusps with varying degrees of calcification. Detailed scrutiny of the erupted M 1and M’ reveals marked differences in the morphology and size of these molars amongst the anthropoid apes and man. Although there are differences in these molars at the time of birth, they are not as dissimilar as are the erupted forms. The traits that distinguish the molars of the various species are present on the newborn bud but are attenuated. Mensurational data are presented in a graphic form to illustrate trends in growth.

INTRODUCTION THE

MOLAR crown pattern of primates, both fossil and modern, has been of great importance to palaeontologists in reconstructing the phylogeny of this order. Relationships between pre-Pleistocene primates and the modern hominoids were established, for the most part, by comparing the morphological characteristics of the jaws and teeth. This, of course, is due to the fact that teeth and denser portions of the jaw bones of juvenile or adult animals are often the only fossilized structures found. In some instances, teeth constitute the only surviving remains; consequently, primate dental crown morphology has been extensively studied, and differences or similarities of the adult crowns have been accepted as being significant in assessing the degree of affinity between the various forms. Until recently, the dental analysis of the extant primate species, including man, has focused upon the completed forms of the dentition, and consideration of the morphogenesis of the described traits was neglected. Yet it is clear that an evolutionary interpretation can be more firmly established by the dentition if its mode of growth is known. Unfortunately this is not demonstrable for the extinct species. The problem is approachable, however, by examining the morphogenetic patterns of the contemporary primate species, including man. An approach in this direction was initiated by KRAUS (1959) who extracted, cleared and stained whole tooth buds from human foetuses and described the differential

639

640

S.

W. OKA AND B. S. KRAUS

calcification rates in the deciduous molars. Subsequent studies elaborated in greater detail the ontogeny of the human dentition prior to birth (KRAUS and JORDAN, 1965; KRAUS, 1963). These studies established baselines for further comparative studies of primate odontogenesis. Similar studies have been initiated for the baboon and the rhesus (SWINDLER, 1961; SWINDLER and GAVAN, 1962; SWINDLER and MCCOY, 1965; SWINDLER, ORLOSKY and HENDRICKX, 1968). However, for man’s closest relatives, the anthropoid apes, comparative odontogenetic studies have not yet been undertaken. A detailed knowledge of the morphogenesis of the dentition from this particular group of primates might contribute significantly to a better understanding of the evolution of the family Hominidae and the establishment of a taxonomy that would reflect such a process. It is the purpose of this paper to compare the first permanent molars of the gorilla, chimpanzee, orangutan, gibbon, and man at the circumnatal and eruptive stages, and to describe in detail their crown morphology. For each species, the nature and amount of growth and maturation achieved from birth to eruption will be described. In addition, the molar crowns of the five species will be compared at the two stages. Special features of the adult molar crown that are extensively described in the literature (viz. the buccal and lingual cingula) will be looked for on the newborn foetal bud to determine if these traits exist at an early stage. Finally, metrical data will be used to determine and compare the directions and rates of growth of the molars from birth to eruption. Although the paucity of anthropoid ape specimens prevents the establishment of statistical norms and ranges for these crowns either at birth or at eruption, it was felt nevertheless that some tentative suggestions might be useful to illustrate the value of comparative ontogenetic data for evolutionary study.

MATERIAL

AND METHODS

Term or near-term foetuses of the Superfamily Hominoidea (SIMPSON, 1945) were obtained from the various sources listed in Table 1. The age, sex and species, when known, are also included. The erupted molars were selected with care to obtain only those specimens showing little or no occlusal wear. The human and gorilla molars were newly erupted teeth; those of the chimpanzee and gibbon showed completely formed crowns but were unerupted, and the orangutan molars were selected from a skeletal collection. The permanent upper and lower first molar buds were extracted from the circumnatal specimens, stained with alizarin red-S, and preserved in 50 per cent glycerine. All of the extracted buds were drawn at x 6.0 using a Wild M-5 stereo microscope with a camera lucida attachment. Photographs of each bud were taken from the occlusal and lingual views (Figs. 3 and 4). The drawings were used in determining the locations of the cusp tips and the angles between them to illustrate graphically the interspecies differences as well as the intraspecies changes in cuspal topography from the circumnatal period to eruption. Photographs of the adult molars (Figs. 1 and 2) were made from casts to eliminate highlights, thereby gaining more topographic detail. Camera lucida drawings

5 days Term

Cheyenne Mountain Zoological Park Aeromedical Research Laboratory Holloman Air Force Base United States National Museum United States National Museum Cleft Palate Research Center Term 16days Term

Age

Source

Circumnatal

F M ?

F F

Sex

USED

THE

Source

IN

Juvenile

STUDY

United States National Museum United States National Museum Cleft Palate Research Center

Pittsburgh Zoological Society United States National Museum

SPECIMENS

3-4 yr ? a 7 yr

4 yrs a 3.5 yr

Age

F M M

F M

Sex

* The species is not known, the record stating only that it was a hybrid animal that died 16 days after birth, presumably in captivity. The juvenile gibbon was captured in the wild in Borneo. According to the recent geographic distribution of the hylobatids published by FRISCH (1965), the animal is most probably Hylobates moloch.

Pongo pygmaeus Hylobates sp.* Homo sapiens

Pan troglodytes

Gorilla gorilla

Specimen

TABLE 1. SOURCE, SEX AND AGE OF THE PRIMATE

3

E n F $

5

g

2

E 5 F Y

6

2

i%

-I

642

S. W. TABLE

2. TNTERCUSPALAND CROWN MEASUREMENTS OF THE ERLJFTED MANDIBULAR PERMANENTMOLARS (IN MM) Dimensions

’

!? 2 ”

OKA AND B. S. KRAUS

Mes-Mes Dist-Dist Bucc-Bucc Ling-Ling DB-Dist DL-Dist

(a-b) (e-d) (a-e) (b-d) (e-e) (d-e)

Max A-P length Max trigonid Max talonid

(B-F) (A-B) (C-D)

Orangutan

Gibbon

5.5 7.3 4.8 6.5 3.6 5.9

6.0 6.4 5.2 7.2 3.7 4.8

3.4 4.4 3.8 4.1 2.3 2.7

15.5

11.8

11.0

6.9

12.5 12.3

9.8 9.5

10.0 10-o

5.2 5.4

Human

Gorilla

5.0 6.0 4.4 5.0 3.8 4.6

7.2 7.8 6.3 7.1 3.9 5.5

11.4

10.0 9.7

Chimpanzee

TABLE 3. INTERCUSPALAND CROWN MEASUREMENTS OF THE CIRCUMNATAL FIRST PERMANENTMOLARS (IN MM)

Dimensions

7 2 @ g 2

$ 2 cI

Mes-Mes Dist-Dist Bucc-Bucc Ling-Ling DB-Dist DL-Dist

(a-b) (e-d) (a-e) (b-d) (e-e) (de)

Max A-P length Max trigonid Max talonid

(B-F) (A-B) (C-D)

RIGHT FIRST

MANDIBULAR

RIGHT

Human

Gorilla

Chimpanzee

Orangutan

Gibbon

3.6 4.0 3.9 3.8 2.0 3.5

5.1 4.7 4.7 4.4 2.9 2,7

4.4 4.4 3.6 3.5 2.1 3.1

4.4 4.5 4.2 4.9 2.6 3.7

2.7 2.2 3.1 3.3 I.4 1.3

7.0

9.2

6,6

8.8

4.5

6.1 6.9

7.4 6.1

5.8 5.6

6.8 6.5

3.7 3.2

TABLE 4. INTERCUSPALAND CROWN MEASUREMENTS OF THE ERUPTEDMAXILLARYRIGHT FIRSTPERMANENT MOLARS (IN MM)

Dimensions

Human

Gorilla

Chimpanzee

Orangutan

Gibbon

7 3 a JZ ,o

Mes-Mes Dist-Dist Bucc-Bucc Ling-Ling

(a-b) (e-d) (a-c) (b-d)

6.3 5.8 5.0 4.4

8.9 9.2 7.6 6.6

7.5 8.6 5.8 5.9

6.9 6.6 5.6 5.5

4.1 4.7 3.0 3.0

g ”LI

Max A-P length Max trigon Max talon

(B-F) (A-B) (C-D)

10.4 11.5 10.5

14.5 14.4 13.5

11.4 11.8 11.4

11.5 11.5 11.0

6.4 6.4 6.6

THE CIRCUMNATAL STATUS

OF MOLAR

CROWN

643

MATURATION

TABLE 5. IN~RCUSPAL AND CROWN ~~EAsuREMENTS OF THE CIRCUMNATAL MAXILLARY FIRST PERMANENT

Dimensions

MOLARS

(IN

RIGHT

MM)

Human

Gorilla

Chimpanzee

Orangutan

Gibbon

‘ii $ $ 2 c(

Mes-Mes Dist-Dist Bucc-Buce Ling-Ling

(a-b) (e-d) (a-c) (b-d)

4.2 3.8 3.2 3.0

5.4 5.5 5.0 4.4

5.6 5.2 4.1 4.1

5.5 4.5 4.4 4.4

3.5 3.2 2.3 2.6

2 6

Max length A-P Max trigon Max talon

(E-F) (A-B) (C-D)

5.8 6.4 5.6

7.6 7.2 6.8

6.0 6.9 5.7

6.7 7.5 6.6

4.9 4.4 3.9

were also made of the adult molars; however, the original tooth rather than the cast was used for measurements. Measurements of the circumnatal molar buds and completed crowns are listed in Tables 2-5. These measurements are not represented as means for the size of the molars of the Hominoidea [it is known that a great variation has been reported (ASHTON and ZUCKERMAN, 1950; SCHUMAN and BRACE, 1955)] but are merely random samples of one each from the respective populations. It is reassuring to note that metrical data for the completed crowns fall well within the ranges reported by other authors (op. cit. 1950, 1955). A schematic drawing illustrating the reference points and the dimensions measured on the upper and lower molar at the circumnatal and the erupted stage is presented in Fig. 5. The measurements of the adult molars were made directly on the tooth itself with a standard Boley gauge accurate to 0.10 mm. The molar buds of the newborn were BUCCAL

BUCCAL A

B D

D

B LlNGUAL

LlNGUAL

MAXILLARY

MANDIBULAR

FIG. 5. Drawing to illustrate odontometric landmarks and dimensions on the maxillary and mandibular crowns of the first permanent molars.

S. W. OKA

644

AND B. S. KRAUS

measured with a Bausch and Lomb filar micrometer attached to a zoom stereodissecting microscope. The variable resolution of the scope permitted the adjustment of the scale on the filar micrometer to equal exactly the scale on the Boley gauge. Intercuspal measurements were made parallel to the occlusal plane. The maximum length (E-F) was measured parallel to the occlusal surface between the greatest mesial and distal convexity of the completed crown or developing bud. The mesial and distal widths, A-B and C-D, respectively, were measured at right angles to the maximum length. The newly erupted adult form of the molar crowns are described first, followed by a description of the morphology of the circumnatal molar crowns. In each case the mandibular molars are described first, then the maxillary with the order of the species remaining the same throughout as listed in the tables and figures. Patterns of calcification will be described together with the morphology of the circumnatal molar crowns in order to avoid unnecessary repetition. MORPHOLOGY (a) The Erupted Molar Crowns

(i) The mandibular first molar Man. The human mandibular first molar is more or less pentagonal, with a distal apex formed by the hypoconulid. The trigonid is slightly wider than the talonid. The difference between the maximum length and the maximum breadth (trigonid) of the crown is the least of all of the species reported in this series. The observed measurements correspond very closely to those reported by WHEELER (1958). The occlusal surface exhibits relatively few accessory ridges or “wrinkles” as compared to the molars of the gorilla, chimpanzee, and especially the orangutan (WEIDENREICH, 1945; KRAUS and OKA, 1967). The cusps are well developed and rounded, separated by deep and well defined developmental grooves. The cuspal disposition of the specimen is the “Y5” Dryopithecus pattern (GREGORY and HELLMAN, 1926) found in higher frequencies among Mongoloids (DAHLBERG, 1949). The largest cusp is the protoconid, although when viewed only from the occlusal surface, it is rather difficult to assess the relative sizes of the five cusps. The metaconid and the entoconid appear to be approximately equal in size. The hypoconid and the hypoconulid sizes are also approximately equal; however, the latter is usually the smallest cusp on the tooth. The position of the hypoconulid is slightly towards the buccal surface. The buccal and lingual surfaces are smooth and devoid of any traces of a ledge or cingulum. Gorilla. The occlusal view of the gorilla lower molar exhibits the five cusped “Y5” Dryopithecus form. Well-defined heavy ridges course from the sharp cusp tips to the occlusal basin obscuring the developmental grooves. A deep constriction between the protoconid and hypoconid easily distinguishes the gorilla molar from the human molar. This buccal constriction does not have a lingual counterpart and therefore prevents a separation into mesial and distal moieties as in the Ccrcopithecoid bilophodont molar. The occlusal shape is rectangular, and is longer relative to its breadth as compared

THE

CIRCUMNATAL

STATUS

OF

MOLAR

CROWN

MATURATION

645

to the human and the other pongids. The apex of the hypoconulid on the gorilla molar is placed bucally, and the distal occlusal outline is square with a heavy marginal ridge. The buccal cingulum is variable in size on the buccal surface. It is present as a distinct ledge on the mesial portion of the protoconid and continues distally on the buccal surface as a slight ridge. The distal corner of the hypoconulid is the most distal portion of the cingulum and is again a distinct ledge. The mesial and distal marginal ridges are well defined, heavy, and continuous with the ridges on the cusp tips. There are two heavy ridges on the mesial moiety of the molar crown connecting the protoconid and the metaconid. They appear as distinct ridges forming a “V” shaped through bridging the two mesial cusps. The most anterior of these ridges just distal to the mesial marginal ridge, was designated the anterior trigonid crest, and the second more distal one was named the posterior trigonid crest by REMANE (1921). The basin, or trough, between the ridges connecting the two mesial cusps is the trigonid basin. Considerable attention was paid to the nomenclature and the derivation of these ridges by WEIDENREICH (1937) who considered the mesial marginal ridge proper to be the anterior trigonid crest. The mesial of the two accessory ridges he referred to as the posterior trigonid crest, and the most distal ridge on the trigonid, he considered to be a “secondary inconstant acquisition”. The presence of these ridges will be noted on the molar bud of the newborn gorilla. The cusps of the mesial moiety are nearly equal in size. Of the three cusps on the distal portion of the molar, the hypoconulid is the smallest with the entoconid and the hypoconid approximately equal in size. Chimpanzee. The lower first molar of the chimpanzee is much closer in size to the human molar in its total dimensions and it has been stated that it is difficult to distinguish the chimpanzee molar from that of man (SCHUMAN and BRACE, 1955). There are however, discrete morphological differences between these two molars. The chimpanzee molar is much like the gorilla molar in cusp morphology. They have sharp and welldefined intercuspal ridges contrasting with the more rounded cusps on the human molar. The occlusal outline is rectangular and the distal portion does not end in a triangular apex as in man but in a straight distal margin similar to the gorilla. The typical “YS pattern is apparent from the occlusal view. The chimpanzee molar is morphologically more similar to the gorilla than it is to the human lower molar. However, if there is some wear on the tooth, it would be difficult to distinguish the chimpanzee molar from that of man. Two accessory ridges distal to the mesial marginal ridge connect the two cusps of the mesial portion of the molar as on the gorilla. The ridges are not as heavy as those found on the gorilla molar, but are nevertheless distinct with a deep furrow (trigonid basin) between them. The cusp tip topography (Fig. 6) reveals that the two buccal cusps are not oriented in a straight line. The hypoconid is displaced bucally, and the hypoconulid is therefore located just beyond a line drawn parallel to the long axis distally from the cusp tip of the protoconid. The metaconid appears to be the largest cusp when viewed from the occlusal, and the hypoconulid is the smallest. The three remaining cusps are intermediate and are approximately equal in size. rt.0.B.14/6-F

S. W. OKA

646 hlAXILLAF?Y OUCiclL

AND B. S. KRAUS

0

d

b

-

d

---.__

ilNG”.Qi

HUMAN

GORILLA

-

CHIMFANZEE

FIG. 6. Changes in the relative cuspal topography eruption.

ORONGUTAN

in the Hominoidea

GIBCC/

from birth to

Orangutan. The orangutan lower molar is quite distinct in its gross morphology in the unworn state. The cusps tips are not as prominent as in the rest of the pongids, hylobates, and man, but are rounded with broad shoulders. The most obvious characteristic of the orangutan molar is on the occlusal surface. There are numerous wrinkles or crenulations extending to the cusp tips, and are quite distinct from the ridges on the gorilla and the chimpanzee molars. The wrinkles on the orangutan molars are distributed throughout the occlusal surface whereas the accessory ridges on the gorilla molar are heavier and not as numerous. Viewing the tooth from the occlusal surface, the shape of the molar is rectangular. The mesial and distal portions of the molar are equal in width (Table 2). In size, the orangutan molar is slightly smaller than in the chimpanzee, although the difference is not great enough to put it outside its metrical range. The cusp arrangement is the same as in the other anthropoid molars although the Dryopithecus pattern is hard to distinguish due to the profuse occlusal wrinkling. The developmental grooves that separate the cusps are barely discernable as a furrow between them. Occasionally a fine groove may separate the cusps, as seen between the entoconid and the hypoconulid. The position of the lingual cusps is more distal than the other anthropoid molars resulting in a buccal displacement of the hypoconulid (Fig. 6). Gibbon. The lower molar of the gibbon is the smallest of the Hominoidea molars and is almost one half the size of the gorilla, which is the largest (Table 2). The variations found in the morphological pattern of the gibbon molar is considerable and was extensively studied by FRISCH (1965). The main body of his study deals with the upper molars and scant information is presented on the morphological variations of the

THE

CIRCUMNATAL

STATUS

OF

MOLAR

CROWN

MATURATION

647

lower molars. The specimen described in this paper most likely belongs to the subspecies, Hylobates molochfunerus, which ranges in Borneo, (FRISCH, 1965) and although its morphology may be applicable to gibbon molars in general, it must be emphasized that there are apparent variations among this group in detailed morphology and absolute measurements. From the occlusal view (Fig. 1) the typical five-cusped pattern of the mandibular molars of the Hominoidea is apparent. The tips of the cusps are located near the periphery of the tooth and almost forms its extreme margins. The tooth is shaped somewhat like a parallelogram with the acute angles located at the mesiobuccal and the distolingual corners. The cusps are rather rounded and are more similar to the human cusps than to the pongids. The developmental grooves separating the cusps are deep and well defined and meet at the central portion or the occlusal surface forming a central pit. The occlusal surface is free of wrinkling and folding, although accessory ridges can be seen on the cusps. These ridges are more apparent on the metaconid and the hypoconulid. The entoconid is displaced lingually leaving a wide basin where the base of this cusp joins the bases of the hypoconid and the hypoconulid. The hypoconulid is situated approximately at the midpoint between the hypoconid and the entoconid (Fig. 6). (ii) The maxilIaryJirst molar Man. From the occlusal aspect, the maxillary molar is somewhat rhomboidal. The outline of the cusp tips also follow this pattern (Fig. 6). The acute angles are located at the distolingual and the mesiobuccal corners. The four cusps are well developed with the protocone the largest cusp. In order of diminishing size, they are: paracone, metacone, hypocone and occasionally, if present, the cusp of Carabelli. There is a well-developed oblique ridge connecting the protocone to the metacone and is broken at its midpoint by a developmental groove (transverse groove), which is not present on the upper molars of the pongid and hylobatid molars. There is a slight cusp of Carabelli confined to the lingual surface of the protocone. The hypocone is separated from the cusps of the trigon by a deep distal oblique groove which continues down the lingual surface separating the hypocone from the protocone. This groove is also present on the gorilla, chimpanzee and gibbon although it terminates at the level of the lingual cingulum. In the orangutan the groove is not readily apparent but is present as a slight depression on the lingual surface. Gorilla. The first molar in the gorilla is reported to be the smallest of the three molars, (JAMES, 1960) and it shares this characteristic with the gibbon. The outline of the occlusal is rhomboid with the greatest prominence on the buccal surface of the largest cusp, the paracone. As with the lower molar, there are welldefined accessory ridges. Intercuspal grooves are not a prominent feature, although there is a deep groove separating the hypocone from the protocone. Instead of a transverse groove intervening between the protocone and the paracone, these cusps are joined at the base on the occlusal surface. The crest connecting the two cusps has been identified as the crista transversa anterior by KORENHOF (1960). He also locates the

648

S. W.

OKA

AND

B. S. KRAUS

remnant of the protoconule on the crest as a “slight tumescense”, and may or may not occur in some specimens. The hypocone is well developed. A cingulum is present along the whole lingual surface from approximately the middle of the hypocone and terminating on the mesial surface of the protocone almost to the midpoint of the mesial margin of the tooth. The marginal ridges are well-developed and forms a continuous ridge connecting the cusp tips. There is no buccal cingulum. Chimpanzee. The occlusal outline of the upper molar of the chimpanzee is rhomboidal, with the acute angles located at the mesiobuccal and the distolingual corners of the tooth. Although all of the upper molars of the adult of the Hominoidea can be represented as roughly rhomboidal, the chimpanzee upper molar has the most acute angles at the mesiobuccal and the distolingual corners of all the pongid upper molars in this sample. The occlusal surface of the chimpanzee upper molar, like the lower molar, has numerous ridges extending from the cusp tips to the base of the cusps. The oblique ridge is much more prominent on the chimpanzee upper molar than on the gorilla, and is much sharper than on the human molar. The mesial marginal ridge is irregular but does not have prominent cusplets. There is a slight ledge between the two buccal cusps on the buccal surface and is apparently a variation of the buccal cingulum. The buccal cingulum is extensively described for the upper first permanent molars of the chimpanzee and is reported to be a primitive characteristic (REMANE, 1960.) From the lingual view, a cingulum can be seen extending from a point just mesial to the midpoint of the lingual surface of the protocone to the mesial marginal ridge. This may be observed as a “reduced” cingulum and is certainly not as well developed as the cingulum of the gorilla upper molar in this series. Orangutan. The upper molar of the orangutan has the typical rhomboid shape. The angles at the mesial buccal and distal lingual corners are not as acute as in the gorilla and the chimpanzee, and is closer to the human in occlusal outline. In overall size, it is larger than both the human and the gibbon and smaller than the gorilla, and is approximately the same size as the chimpanzee molar. The cusps are low without sharp apices, and the buccal and lingual surfaces are smooth and rounded. The maximum length of the tooth and the diameter of the mesial and distal moieties are all within 0.5 mm making it almost an equilateral tooth. In this respect it is very similar to the chimpanzee upper molar. The occlusal surface is characterized by profuse wrinkles. The developmental grooves that are so well-defined on the human molar are obscured on the orangutan molar. A furrow is the only trace and it is most prominent between the protocone and the hypocone as the lingual groove and continues on the occlusal surface distal to the oblique ridge. The lingual surface is smooth with no trace of a lingual cingulum. WEIDENREICH (1937), states that the lingual cingulum is least developed in the orangutan. KORENHOF (1960, p. 110 and 135) cites SELENKA(1898) on the presence of a tubercle on the mesial lingual margin. Selenka called this the tuberculum accessorium anterius internum, and declared that it was found in the majority of Pongo upper molars and reaches the greatest size in this species. The photograph (Fig. 2) shows a slight prominence on the mesial marginal ridge towards the protocone.

THE

CIRCUMNATAL

STATUS

OF

MOLAR

CROWN

MATURATION

649

Gibbon. The occlusal outline of the gibbon upper molar is more rounded in appearance than the pongid and human molars, although if lines tangential to the most prominent portion of the external borders were drawn, a vaguely rhomboid figure like the pongid upper molar can be described. The most acute angle of the resulting figure will be located at the distolingual corner, where the well-developed hypocone extends conspicuously to the lingual. Although in all measurements the gibbon is by far the smallest upper molar in this series, there is an additional inter-molar size relationship that distinguished the gibbon upper molar from those of the pongid and man. Of all the upper molars of the Hominoidea, the gibbon molar is the only one in which the talon width is greater than the width of the trigon. The pongid and human upper molar, on the other hand, has a talon width that is nearly equal to or less than the width of the trigon (Table 4). The lingual surface has a clearly-defined cingulum running from the distal border of the hypocone to the mesial border of the protocone. FRISCH (1965) reports that there are differences in the expression of the lingual cingulum depending on the region of a single subspecies. Hylobates moloch funerus, according to his study, shows a gradient in the expression of the lingual cingulum relative to its geographical range, those from Northeast Borneo showing more reduction of the cingulum that those from the north or from the east of Borneo. Of the upper molars of the Hominoidea, the cingulum appears to be more defined on the gibbon, and extends further mesiodistally along the lingual surface. FRISCH (1965) concludes that: “. . . . on the whole, the Hylobatids have suffered a less intensive reduction of the cingulum than the pongids.” (b) The Circumnatal Molar Crowns (i) The mandibular first molar Man. The occlusal outline of the human permanent first molar bud is almost a square; the difference in measurement of the maximum anterior-posterior length to the maximum breadth (trigonid, A-B) is in the order of I.4 mm. The cuspal topography (Fig. 6) reveals the amount of change in the outline from birth to eruption. The hypoconulid is displaced more to the buccal during the circumnatal period. The permanent lower first molar has been described as having one to three cusps calcified at birth (CHRISTENSENand KRAUS, 1965). The single specimen described here has initial calcification commencing on three cusps, the protoconid, hypoconid, and the metaconid. Calcification of the protoconid has progressed nearly to the occlusal basin and is the most advanced of the three cusps. The metaconid is slightly more advanced than the hypoconid. The order of calcification follows the above sequence and agrees with that reported by others (CHRISTENSENand KRAUS, 1965). Sharp intercuspal ridges join the protoconid, hypoconid and the hypoconulid. Heavy transverse ridges between the mesial cusps are not present as in the gorilla; these cusps are connected by the mesial marginal ridge which, extending from the mesial portion of each cusp, forms the most mesial border of the bud. The metaconid and entoconid are connected by a ridge which forms the lingual margin of the tooth bud. The occlusal basin is relatively smooth, although not as free from irregularities as the gibbon bud.

650

S. W. OKA AND B. S. KRAUS

A distinct ledge can be seen on the buccal surface extending from the mesial marginal ridge to the hypoconulid. This shelf is half the way down the buccal surface and forms the most buccal prominence of the molar bud. Gorilla. The developing first molar of the gorilla is shaped roughly like a trapezoid lying on its side. The widest portion is at the mesial. The distal outline is rounded. There is a marked constriction on the buccal surface and a lesser one on the lingual. Three cusps are calcified, the protoconid, metaconid, and the hypoconid. The protoconid is most advanced in calcification, and the hypoconid the least advanced. The cusps and the order of calcification at this stage of development is identical to the human lower molar. Sharp intercuspal ridges connecting the cusps on the exterior margins are supplemented by additional intercuspal crests on the occlusal basin. On the mesial moiety, two well-defined ridges or crests, connect the protoconid and the metaconid. The most mesial of the two ridges extends from the occlusal portion of the protoconid to the mesial border of the metaconid and merges with the mesial marginal ridge at that point. The more distal of the two ridges connects these two cusps at about two-thirds of the distal occlusal border. These ridges form the anterior trigonid crest and the posterior trigonid crest of the completed adult molar. The hypoconid is connected to the hypoconulid by a sharp ridge. The entoconid and the hypoconulid, both uncalcified at this stage, exist as sharp, conical, well-defined points on the molar bud with two sharp ridges connecting them. One ridge extends from the distal margin of the hypoconulid to the most distal portion of the entoconid from cusp tip to cusp tip. The more mesial of the two ridges extends from the middle of the hypoconulid to the middle portion of the entoconid. There are several sharp ridges on the occlusal surface originating at the base of the calcified cusps and terminating in the occlusal basin. They are not as numerous as those seen in the orangutan but are heavier and more defined. There is a ridge on the buccal surface forming a shelf. This shelf extends all along the buccal border to the tip of the hypoconulid and forms the distal ridge. Chimpanzee. The occlusal view of the lower molar reveals that three cusps are calcified. They are the protoconid, the metaconid, and the hypoconid. The overall shape of the bud is roughly a parallelogram with the acute angles at the mesiobuccal and the distolingual corners. There is a constriction on the buccal surface between the two buccal cusps and a lesser constriction opposite to it on the lingual surface. The width of the mesial and distal moieties are approximately equal. This is in contrast to the gorilla tooth bud which has a narrower talonid. The hypoconulid is a small, sharp tip situated slightly to the buccal but not as extremely as in the human or the orangutan molar buds. The entoconid shows no signs of calcification. There are two barely-discernable ridges connecting the mesial cusps. They are not as sharp and well-defined as those found on the gorilla molar bud, but are homologous to them. The crest on the talonid between the entoconid and the hypoconulid on the gorilla lower molar is absent on the chimpanzee lower molar. The extention of the buccal surface is minimal with only a slight ledge beyond the intercuspal ridge between the protoconid and the hypoconid.

THE

CIRCUMNATAL

STATUS

OF MOLAR

CROWN

MATURATION

651

Orangutan. The occlusal shape of the orangutan molar bud is a rounded rectangle. Four cusps have begun calcification. The most advanced is the protoconid, where calcification has extended to the occlusal basin. The metaconid has a broad area of calcification and a finger of calcified tissue extends three-quarters down the transverse ridge. The hypoconid is next in order in the amount of calcification, and finally the entoconid which has the barest evidence of calcification at the tip. The hypoconulid is not calcified but is a small sharp prominence that is displaced towards the buccal. In this respect, the position of the hypoconulid differs markedly from the gorilla and the gibbon. There is only one well-defined ridge connecting the two mesial cusps. This ridge can be followed from the calcified extention of the metaconid to the protoconid. The talonid crest between the entoconid and the hypoconulid can be clearly seen mesial to the distal marginal ridge, and with it forms a shallow basin between the two cusps. The occlusal basin is shallow and shows a series of minute irregularities on the surface. This is evidence for the early development of the wrinkles peculiar to the orangutan (KRAUS and OKA, 1967). There is a bulbous prominence on the buccal surface, but it is not sharply defined as a ledge. Gibbon. The gibbon molar bud is the smallest of the five species, the bud is trapezoidal in shape with the base at the mesial. The cusp tips are spread out and form the outermost margin of the bud. Calcification has begun on four cusps with coalescence between the mesial cusps. The hypoconulid is the only cusp uncalcified and is situated at the midpoint on the distal margin. The gibbon is the oldest specimen in the series and may account for the advanced state of calcification. The occlusal surface is smooth and free from irregularities. There are no accessory transverse ridges on the trigonid or the talonid. The extention of the buccal surface is minimal and there is no evidence of a buccal cingulum. (ii) The maxillary first molar Man. The overall occlusal outline of the molar bud has an irregular rounded appearance with an acute displacement towards the buccal at the mesiobuccal comer. The paracone, metacone and the protocone have begun initial calcification. The paracone is most advanced in calcification. The metacone and the protocone are nearly equal in the amount of calcification. The hypocone is small and is present as a small uplifted tip at the distolingual corner. The mesial marginal ridge has a slight irregular outline with a small cusplet just lingual to the paracone. The oblique ridge is well developed and extends from the tip of the metacone to the tip of the protocone. BUTLER (1967) describes a “minor ridgelike elevation, lingual to the paracone” which is not always present. This specimen does not show this feature. A slight ledge can be seen on the lingual of the protocone and is the most lingual portion of the bud. At this stage of development, it appears to be relatively larger than its analogue on the pongid and hylobatid upper molar buds. The buccal margin bulges well beyond the cusp tip and forms a slight ledge. Gorilla. From the occlusal surface, the bud exhibits roughly a rhomboid configuration. There are three cusps calcified; the most advanced is the paracone. The protocone

652

s. w.

OKA

AND

B. s. KRAUS

is slightly more advanced than the metacone in calcification. The ridges are sharp and well-defined. The oblique ridge forms the distal limit of the trigon and extends to the tips of the metacone and protocone. There is an additional intercuspal ridge that connects the protocone to the hypocone. The lingual cingulum extends from the mesial marginal ridge to the lingual border of the hypocone. It forms the most lingual aspect of the bud. A slight buccal ridge which appears to be a buccal cingulum extends three-quarters of the way down the buccal border and runs from the most buccal portion of the metacone to the most buccal aspect of the paracone. The mesial marginal ridge flares out sharply and forms the most mesial aspect of the bud. There is one mesial marginal ridge cusp midway between the paracone and the protocone. Distal to the mesial marginal ridge is a slight crest that connects the protocone to the paracone. This ridge is also found on the chimpanzee crown. Chimpanzee. The occlusal outline of the tooth bud is rhomboid with the acute angles at the mesiobuccal and mesiolingual corners. The cuspal outline (Fig. 6) follows a similar pattern. The paracone, protocone, and the metacone exhibit calcification with the paracone the most advanced. The hypocone is a small and pointed uplifting on the most lingual surface of the distal lingual extension. Joining the paracone and protocone, is a ridge just distal to the mesial marginal ridge. This ridge is probably the crista transversa anterior. A sharp oblique ridge runs from cusp tip of the protocone to the cusp tip of the metacone. A ridge connects the protocone to the hypocone as in the gorilla upper molar bud. There is a small ledge along the lingual surface of the protocone, and is widest near the mesial portion of this surface. This ledge continues as a slight ridge distal to the hypocone. Orangutan. This bud is almost square in the occlusal outline with a large mesiobuccal bulge. The paracone is most extensively calcified, while the protocone and the metacone exhibit calcification only on the tips. The hypocone is uncalcified and is a fine point on the distolingual corners of the molar bud. The oblique ridge is low and has a sharp crest and extends from the tip of the metacone to the most distal aspect of the protocone. The mesial marginal ridge is irregular with a series of small extension that gives the edge of the ridge a scalloped appearance. A small cusplet is located on the ridge, lingual to the midline, towards the protocone. A slight mesial ridge connects the hypocone to the protocone. There is a swelling on the lingual surface of the protocone which merges with the mesial marginal ridge on the mesial, and extends distally as a vague ridge to the tip of the hypocone. Gibbon. The occlusal outline of this molar is square with a cusp on each corner. All four cusps exhibit calcification. The paracone, protocone and the metacone are calcified to the base, with extensions commencing along the ridges. Calcification on the hypocone has not progressed as far as on the other cusps. The position of the hypocone is quite distal and it contributes to the square appearance of the molar. The mesial marginal ridge is sharp and regular without accessory cusplets. Just distal to it is a sharp ridge connecting the two mesial cusps with calcified extensions from the paracone and the protocone. Bridging of the cusps will occur on this ridge. The oblique ridge is

not prominent absent absent

to lingual cingulum present but reduced

Buccal cingulum

slight ledge between cusps

absent

almost to CEJ

carabelli tubercule

Distal oblique ridge

Lingual cingulum

and

present

interrupted by transverse groove

Oblique ridge to lingual cingulum

rhomboid sharp cone obscured by ridges

continuous rounded

rectangular low and rounded obscured by crenulations absent absent one

Orangutan

continuous and well defined

rectangular sharp cone obscured by ridges absent absent two

Chimpanzee

continuous and well defined

MAN

rhomboid low and rounded obscured by crenulations

AND

AND MAXILLARYFIRST PERMANENTMOLARCROWNS

rhomboid sharp cone obscured by ridges

rectangular sharp cone obscured by ridges present absent two

rhomboid rounded deep and well defined

pentagonal rounded deep and well defined absent absent one

Gorilla

MANDIBULAR

Occlusal outline Cusp shape Developmental grooves

Maxillary crowns

Buccal cingulum Lingual cingulum Number of trigonid ridges

Occlusal outline Cusp shape Developmental grooves

Mandibular crowns

Man

TABLE 6. TRAITS CHARACTERIZJNGTHE COMPLETED

APES

absent

present

to lingual cingulum

sharp and continuous

rounded rounded cone deep and well defined

parrallelogram sharp and spread out deep and well defined absent absent one

Gibbon

OF THE ANTHROPOID

Occlusal outline Cusp shape Number of cusps calcified Buccal cingulum Lingual cingulum Intercuspal ridges

Maxillary crowns

Intercuspal ridges

Occlusal outline Cusp shape Number of cusps calcified Buccal cingulum

Mandibular crowns

rounded blunted tip three slight ledge present protocone to hypocone

square blunted tip three ledge on buccal surface absent

Man

rhomboid sharp three slight ridge present protocone to hypocone and paracone to protocone

trapezoidal sharp three ledge on buccal surface two trigonid crests and two crests on talonid

Gorilla

rhomboid sharp three absent present protocone to hypocone and paracone to protocone

parallelogram sharp three slight buccal ledge two trigonid crests

Chimpanzee

square sharp three absent present protocone hypocone

to

rectangle sharp four bulbous buccal prominence one trigonid crest and one talonid crest

Orangutan

TABLE7. TRAITSCHARACTERIZING THECIRCUMNATAL MANDIBULAR AND MAXILLARYFIRSTPERMANENT MOLARCROWNS AND MAN

square sharp four absent present protocone to hypocone and paracone to protocone

absent

trapezoidal sharp four absent

Gibbon

OF THEANTHROPOID APES

THE

CIRCUMNATAL

STATUS

OF

MOLAR

CROWN

MATURATION

655

heavy with extensions of calcified tissue from the lingual of the metacone and the distobuccal of the paracone. A small ridge from the mesial of the hypocone connects this cusp to the protocone. The paracone exhibits the greatest amount of basal extension of calcific tissue along the ridges, and is thus more advanced in calcification than the other cusps. On the other hand, the protocone has the widest base and consequently the greatest surface area calcified. The advanced state of calcification of the trigon cusps renders the assessment of the sequence of calcification difficult; however, it is most likely in the following order; paracone, protocone, metacone and finally the hypocone. There is a heavy shelf along the lingual border starting at the cusp tip of the hypocone and proceeding to the border of the protocone. This shelf is located half way down the lingual surface. A list of the salient features of the eruptive crowns is presented in Table 6 and for the circumnatal crowns in Table 7.

(c) Changes in Crown Size and &spa/

Topographyfi-om

Birth to Eruptiorz

Figures 7 and 8 have been constructed from the mensurational data found in Tables 2-5. The change in size from birth to eruption for each of the five hominoid species is graphically represented in the two figures. This is done in terms of the intercuspal diameters (4 in the maxillary molars and 6 in the mandibular) and three maximum crown diameters. It must be remembered, however, that in each case the increase that is shown is an artificial construct, since the measurements representing birth and

MANDIBULAR

FIRST

MOLAR

15. 14. 13. 12.

a-b

c-d

a-c

b-d

c-e

d-e

E-F

FIG. 7. Increase in size of selected intercuspal and crown diameter of the mandibular molar from birth to eruption for each of five Hominoid species.

656

S. W. OKA MAXILLARY

AND B. S. KRAUS FIRST

MOLAR

I=c

I

14 II

a-b

c-d

a-c

b-d

E:F

A-B

I/ 1

G-D

FIG. 8. Increase in size of selected intercuspal and crown diameters of the maxillary molar from birth to eruption for each of the five hominoid species.

eruption have been taken of molars from two different animals. It is therefore impossible to make any valid statement regarding differences in slope between species as seen in Figs. 7 and 8. On the other hand, there are certain observations which seem pertinent and valid in spite of the inadequacy of the sample and the cross-sectional nature of the data. It is obvious that, in terms of both intercuspal and maximum crown diameters, the rankings of the species in size, both at birth and at eruption, are extremely consistent. The gibbon is always the smallest and in most measurements the gorilla is the largest. Man occupies a position between the gibbon on the one hand, and the orangutan and chimpanzee on the other. As would be expected, from the nature of the measurements, the increase in maximum size of the crown is more marked than the increase in intercuspal diameters. In all intercuspal diameters of both maxillary and mandibular molar crowns, the differences in size between gorilla and gibbon molars are far greater at time of eruption than at birth. This is a fair indication that the growth rate of the first permanent molar in the gorilla is significantly greater than it is in the gibbon. Upon viewing the status of calcification of molars in gorilla and gibbon at birth (Figs. 3 and 4) one might agree that this difference in growth rate is a consequence of the advanced degree of calcification in the gibbon. However, the new-born gibbon specimen, as indicated in Table 1, is of 16 days postnatal age and it is doubtful if growth could have been so rapid in this short period as to nullify the picture revealed in Figs. 7 and 8. It is well-known that ontogenetically the two mesial cusps are the first to appear

THE

CIRCUMNATAL

STATUS

OF

MOLAR

CROWN

MATURATION

657

and are quite well developed before the cusps of the distal moiety of the crown make their appearance. By birth the two mesial cusps are more calcified and are farther apart than are the distal ones. This is apparent from a comparison of the intercuspal diameters at birth of the two mesial cusps (a-b) with the diameters between the two distal cusps (c-d) at birth for each species. By the same token, we would expect a greater rate of growth in the c-d dimensions from birth to eruption, than in the a-b dimensions, since growth between the two mesial cusps is considerably nearer completion. As has been shown by KRAUS and JORDAN (1965), intercuspal growth ceases after calcification coalescence between two cusps. Examination of Figs. 7 and 8 confirms this expectation, in spite of the fact that the sample is small and the data are not longitudinal. Since there was no way of registering the cuspal outline of the molar at birth upon that of the erupted molar, an arbitrary method was devised (Fig. 6). The a-b line between the circumnatal cusps (dotted line) was placed parallel to the corresponding line of the erupted crown (solid a-b line). The circumnatal points a and b were then positioned at equal distances from the erupted points a and b. The remaining points of the circumnatal crown (c and d) were then placed in their proper orientation with reference to points a and b. With this manner of orientation it was manifestly impossible to determine vectors of growth; nevertheless it enabled one to compare the relative change in position of cusp tips, particularly those of the distal moiety of the crown. It was obvious then, that in the maxillary molars the greatest change in cuspal topography from birth to eruption occurs in the gibbon and in man. In the mandibular molars the changes are more dramatic, with the most striking alterations in pattern occurring in the chimpanzee and gibbon. In both upper and lower molars, the gorilla and orangutan undergo the least amount of topographic modification from birth to eruption. Acknowledgemenrs-To Dr. H. SETZER, Division of Mammals, U.S. National Museum, Smithsonian Institution, for the newborn specimens of the orangutan and gibbon, and for the juvenile chimpanzee, orangutan and gibbon. To Dr. W. MEEKER, Cheyenne Mountain Zoological Park, Colorado Springs, for the newborn gorilla specimen, and Col. H. H. REYNOLDS, 6561st Aeromedical Research Laboratory, Holloman Air Force Base, for the newborn chimpanzee. We appreciate the co-operation of the Pittsburgh Zoological Society for making available the dentition of the famous young gorilla, “Lonesome George”, who recently died, and gratefully acknowledge the help of Mr. David Sullivan, Senior Medical Photographer, and Miss Margaret Croup, Medical Artist, for the photographs and drawings. The study was supported in part by grant No. DE-01697 from the National Institute of Dental Research, U.S.P.H.S., and by a grant from the Sybiel Berkman Foundation of Steubenville, Ohio. R&m&-Les premitres molaires permanentes de Pongidae, Hylobatidae et Hominidae sont Ctudikes au moment de la naissance et au stade d’kruption. La calcification des cuspides de ces molaires, g la naissance, est identique dans toutes les espkes, sauf chez le gibbon, oh elle est plus avancke. Les MI des pongidds et de I’Homme ont trois

S. W. OKA AND B. S. KRAUS

658

cuspides calcifiees au moment de la naissance. I1 s’agit des protoconide, metaconide et hypoconide, qui se calcifient dans cet ordre. L’entoconide du germe M1 de l’orangoutang est calcifie a son extremite. L’entoconide de M1 du gibbon est Cgalement calcifie, mais a un degre plus avancd, et les cuspides mtsiales sont reliees par un pont calcifie. M’ a trois cuspides calcifiees au moment de la naissance. Ce sont le paracone, le protocone et le metacone, qui se calcifient dans cet ordre. Le gibbon presente une calcification vari&e des quatre cuspides. L’examen minutieux de Mr et Ml, aprts eruption, montre des differences marquees, en morpho!ogie et en dimension de ces molaires chez les singes anthropoldes et 1’Homme. Bien que ces molaires soient dissemblables a la naissance, ces differences s’accentuent lors de l’eruption. Les caracteres differentiels des molaires des diverses especes existent au niveau du germe dentaire, mais ils sont attenues. Les rtsultats de mensurations, pendant la croissance, sont present& sous forme de graphiques. Zusammenfassung-Die

ersten bleibenden Molaren von Pongiden, Hylobatiden und Hominiden werden zum Zeitpunkt der Geburt und der Durchbruchsstadien verglichen. Die Mineralisation der Hiickerspitzen der Molaren zum Zeitpunkt der Geburt sind bei allen Spezies lhnlich mit Ausnahme des Gibbon, bei dem sie fortgeschritten ist. Die M, von Pongiden und Menschen besitzen zwei zum Zeitpunkt der Geburt mineralisierte Hockerspitzen. Dies sind der Protokonus, Metakonus und der Hypokonus; die Mineralisationsfolge verlauft in dieser Reihenfolge. Der Entokonus am M1-Keim des Orang-Utan ist an der Spitze verkalkt. Der Entokonus des M1 des Gibbon ist ebenfalls, jedoch in grtiBerem AusmaB mineralisiert, und die mesialen Hacker besitzen eine mineralisierte Briicke. Der M’ besitzt drei zum Zeitpunkt der Geburt mineralisierte Hacker. Parakonus, Protokonus und Metakonus werden in dieser Reihenfolge verkalkt. Der Gibbon besitzt alle vier Hiickerspitzen mit unterschiedlichen Graden der Mineralisation. Die genauere Untersuchung des durchgebrochenen M, im Unter- und im Oberkiefer ergibt hinsichtlich der Morphologie und der GrGDe dieser Molaren deutliche Unterschiede zwischen den anthrapoiden Affen und den Menschen. Obwohl es Unterschiede zwischen diesen Molaren zum Zeitpunkt der Geburt gibt, sind sie nicht so unahnlich wie die durchgebrochenen Formen. Die Charakteristika. die die Molaren der verschiedenen Spezies unterscheiden, sind beim Zahnkeim des Neugeborenen vorhanden, jedoch abgeschwacht. MeBdaten werden in graphischer Form dargestellt, urn die Entwicklung des Wachstums zu beschreiben.

REFERENCES ASHTON,E. H. and ZUCKERMAN,S. 1950. Some quantitative dental characteristics of the chimpanzee, gorilla and orang-outang. Phil. Trans. R. Sot. Land, 234, 471484. BUTLER, P. M. 1967.The prenatal development of the human first upper permanent molar. Archs oral Biol. 12, 551-563.

CHRISTENSEN, G. J. and KRAUS, B. S. 1965. Initial calcification of the human permanent first molar. J. dent. Res. 44, 1338-1342. DAHLBERG,A. A. 1949. The dentition of the American Indian, In: Papers on the Physical Anthropology of the American Indian, (Edited by LAUGHLIN,W. S.) pp. 138-176. Viking Fund, New York. FRISCH, J. E. 1965. Trends in the evolution of the hominoid dentition. BibkhcaPrimatologia3, l-130. GREGORY,W. K. and HELLMAN,M. 1926. The dentition of Dryopithecus and the origin of man. Anthrop.

Pap. Am. Mus. Nat. His. 35, 239-355.

JAMES,W. W. 1960. The Jaws and Teeth of Primates. pp. 276. Pitman Medical Publishing Co. Ltd., London. KORENHOF,C. A. W. 1960. Morphogenetical Aspects of the Human Upper Molar, pp. 106, 110, 135. Uitgeversmaatschappij Neerlandia, Utrecht. KRAUS, B. S. 1963. Morphogenesis of deciduous molar pattern in man. In: Dental Anthropology (Edited by BROTHWELL,D. R.) pp. 87-104. Pergamon Press, London. KRAUS, B. S. 1959. Differential calcification rates in the human primary dentition. Archs oral Bioi. 1, 133-144.

KRAUS, B. S. and JORDAN,R. E. 1965. The Human Dentition Before Birth. Lea & Febiger, Philadelphia.

THE CIRCUMNATALSTATUSOF MOLARCROWN MATURATION

659

KRAUS, B. S. and OKA, S. W. 1967. Wrinkling of molar crowns: new evidence. Science, N. Y. 157, 328-329. REMANE,A. 1921. Beitrage zur Morphologie des Anthropoidengebisses. Arch. Nuturgesch. 87, 1-179. REMANE,A. 1960. Zahne und Gebisz. In: Primatologia, Vol. III, pp. 637-846. SCHUMAN,E. L. and BRACE, C. L. 1955. Metric and morphological variations in the dentition of the Liberian Chimp. Non-human Primates and Human Evolution. pp. 61-89. SELENKA,E. 1898. Menschenaffe; I: Rassen, Schldel und Bezahung des Orangutan. Weisbaden: C. W. Kreidel’s Vertag. Cited by Korenhof (1960). SIMPSON,G. G. 1945. The principles of classification and a classification of mammals. Bull. Am. Mus. nut. His. 85, l-350. SWINDLER,D. R. 1961. Calcification of permanent first mandibular molar in rhesus monkeys. Science, N. Y. 134, 566. SWINDLER,D. R. and GAVAN, J. A. 1962. Calcification of the mandibular molar in rhesus monkeys. Archs oral Biol. 7, 727-734. SWINDLER. D. R., ORLOSKY. FRANK J. and HENDRICKX,A. G. 1968. Calcification of the deciduous molars in baboons (P&o anubis) and other primates. J. dent. Res. 47, 167-170. SWINDLER.D. R. and MCCOY. H. A. 1965. Primate odontoaenesis. J. dent Res. 44.283-295. TURNER, E. P. 1963. Crown development in human deciduous molar teeth. Arch; oral Biol. 8, 523540. WEIDENREICH,F. 1937. The dentition of Sinathropus Pekinensis: A comparative odontography of the hominids. Puleont. Sinicu, n.s. D, No. 1 (Whole ser No. 101). WEIDENREICH, F. 1945. Giant early man from Java and South China. Anthrop. Pap. Mus. Nut. Hist. 40, 1-134.

PLATES 1 AND 2 OVERLEAF

THE CIRCUMNATAL

GORILLA

HUMAN

FIG. 1. Occlusal

STATUS OE MOLAR

CROWN

MATURATION

CHIMPANZEE

and lingual views of the adult mandibular

HUMAN

FIG. 2. Occlusal

GORILLA

CHIMPANZEE

OXlaON

ORANGUTAN

first permanent

molar.

ORANGUTAN

GIBBON

and lingual views of the adult maxillary first permanent

molar. PLATE I

A.O.B.

f.p. 660

S. W.

HUMAN

OKA AND B. S. KRAUS

CHIMPANZEE

GORILL4

FIG. 3. Occlusal and

HUMAN

FIG. 4. Occlusai

PLATE 2

lingual

GORILLA

and lingual

views

ORAWUTAN

of the circumnatal molar.

CHIMPANZEE

views of the circumnatal

mandibular

first

OXANSIJTAN

maxillary

first permanent

GIBBON

permanent

GIBBON

molar.