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Dental formulae and dental eruption patterns in parapithecidae (primates Anthropoidea).

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 62363-375 (1983)
Dental Formulae and Dental Eruption Patterns in Parapithecidae
(Primates, Anthropoidea)
RICHARD F. KAY AND ELWYN L. SIMONS
Duke University Medical Center (R.EK.),Durham, North Carolina 27710
and Duke University Center for the Study of Primate Biology and History
(E.L.S.), Durham, North Carolina 27710
KEY WORDS
development
Apidium, Parapithecus, Anthropoidea, Dental
ABSTRACT
The eruption sequence for the lower teeth of Apidium phi+
mense based on 18 juvenile specimens is dP3, dP4, MI, Ma, Pa, P4, (P3, M3), C .
Only five specimens of Parapithecus grangeri show developing lower teeth. P2,
MI, and M2 all erupted before P3 and P4; C and M3 were the last cheek teeth
to erupt. Late eruption of the lower canines in parapithecids is a possible
shared derived resemblance linking these species with Anthropoidea and
Adapidae and distinguishing both from Omomyidae, Tarsiidae, and toothcombed lemurs. Late eruption of M3 in parapithecids is a shared derived
resemblance with Anthropoidea alone.
The lower dental formula of Apidium phiomense is confirmed as 2 . 1 . 3 . 3 by
additional specimens which show the incisors. Based in part on tooth socket
counts, the deciduous lower dental formula was 2.1-3. New specimens of
Parapithecus grangeri now demonstrate a n adult mandibular dental formula
of 0 . 1 . 3 . 3(not 2 . 1 . 3 . 3as previously thought) and a juvenile formula of 1.1.3.
The number of incisors possessed by Parapithecus fraasi is again open to
debate. Material is insufficient to judge whether this species had a pair of
incisors in each lower jaw quadrant, by analogy with Apidium, or had undergone reduction to just one incisor. In any event, the presence of two incisors in
another parapithecid Apidium shows anterior tooth reduction of Parapithecus
grangeri occurred independent of, and should not be considered a shared
derived similarity with, Tarsiidae, as was once thought.
The Parapithecidae is a n extinct family of of additional specimens of Apidium phi+
the Anthropoidea documented thus far only mense, a close relative of Parapithecus fraasi,
from the Oligocene of Africa. The phyloge- showed it to have had a fused mandibular
netic position of parapithecids has long been symphysis and two incisors (Simons, 1967,
a subject of lively debate. For many years 1971, 1972). Simons concluded on this basis
emphasis was placed on Parapithecus fraasi and from reexamination of the relevant specbeing a linking form between Tarsius and imen that the supposed lack of fusion of the
living monkeys and apes, based on a speci- symphysis of €? fraasi was a n artifact of
men which appeared to have a V-shaped breakage and that the hypothesized loss of
mandible, a mobile mandibular symphysis, incisors was only the result of postmortem
and the loss of one lower incisor from each loss of lateral incisors and retention of the
jaw quadrant giving a lower dental formula central incisors. He concluded that the inciof 1 . 1 . 3 . 3 , as in tarsiers. Although addi- sor alveolar borders have been entirely brotional specimens of €? fraasi have now been ken away when the left and right rami were
recovered from quarry M in the Upper Fossil collected.
Wood zone of the Fayum Oligocene, none
gives additional information about the anteReceived March 21, 1983; revised June 8, 1983 accepted June
rior teeth of this species. However, recovery 16,1983.
0 1983 ALAN R. LISS, INC.
364
R.F. KAY AND E.L. SIMONS
On a related front, interest has been renewed recently in the sequence of dental development and eruption of the teeth and its
relevance for establishing tooth homology on
one hand, and phylogeny on the other. Conroy
et al. (1975) reported briefly on the dental
eruption in parapithecids and some of its phylogenetic implicaions. Since then, many additional specimens of Apidium phiomense and
Parapithecus grangeri have been collected
which provide evidence about eruption sequence. Also, a clearer picture of dental eruption sequences in living primates has
emerged. The purpose of this paper is to give
new evidence about the dental formulae and
the sequences of dental eruption in parapithecids and to consider its implication for current
views of their phylogenetic relationships.
APIDIUM PHIOMENSE (FIGS. 1,2,3)
Development of lower teeth
Twenty specimens of A. phiomense have
deciduous teeth andor incompletely erupted
adult teeth. Of these, 18 are mandibles and
two are maxillary fragments. The state of
eruption is shown for 16 of the mandibles in
Table 1 (based on radiographs made a t 56KV,
200 MA for 1 second). Two juvenile mandibles belonging to the Cairo Geological Museum (CGM 18646 and CGM 40153) have not
been fully studied. Eleven mandibles preserve teeth of the left side only and must
belong to different individuals. Of the remaining seven right jaws, all except one have
no left-side counterparts of comparable age.
Thus, a minimum of 17 individuals is
represented.
The earliest represented developmental
stage is seen in YPM 23959, a broken left
mandible preserving dP3, mesial to which
are respectively two broken tooth roots of
slightly smaller caliber than those of dP3, a
single larger broken root socket and two very
small sockets (Fig. 1A). These may be interpreted as roots and sockets for a two-rooted
dPz, a single-rooted dC and two deciduous
TABLE 1. Develovmental data forADidium uhiomense mandibular dentitions
Tooth locus
Specimen No.
YPM 23959l
YPM 209343
DPC 1043
DPC 2942
YPM 23960
YPM 23996
YPM 23997
YPM 23958
YPM 24595
YPM 24597
DPC 1050
YPM 23991
AMNH 11370
YPM 23952
YPM 23948
DPC 1102
dCIC
dP2/P2
dP3P3
-/B4
D2/A
D2/C1
D21C1
D2/C1
D2/C1
DI/A
D2B
D2B
D2B
D2B
-
-
-
-
-
-
D21A
-B4
-B5
-iB5
-iB4
D'IC,
D3n3
-
-
-
-
-n3
-n3
-n3
-iB
EID'
EID'
D'ICz
D~/c~
-
-
-
-
-
-
-
-
EICS
ElDl
EIDl
dP4IP4
Mi
M2
M3
-
-
-
-
d2B
D2B
D2iB
D2B
D2D
- n3
DziB
DzD
-n3
D6/Cz
ElCz
EIC3
Dl
Dl
Di
D1
D1
Dl
D1
DI
DI
D1
Dl
Dl
D1
D2
D1
c2
A
c2
B2
C2-s2
-
-
-
C-D2
B2
B2
B
B-C2
C
C2
ElC3
ED1
C-D2
D1
DI
Di
D1
D1
D1
D1
D6
D1
c2
C
C
D1
Developmental stages: A, tooth not developed; B, tooth in crypt; C, tooth partly erupted: C,, slight migration toward
alveolar margin; C Z .cusp tips a t or near alveolar margin; C3, some cusp-tip wear; D, tooth fully erupted; D,, enamel
worn, not perforated; Dz, enamel perforated in several places; DS, much of tooth surface shows wear; E, tooth reabsorbed
and/or shed.
'Three broken sockets are visible mesial to broken dP' roots: interpreted as two small sockets for dI1, dIz and a larger
one for dC.
'Portion of root or root socket visible but crown hroken away.
3YPM 20934 is misidentified as YPM 20234 in Conroy et al. (1975).
4Mesially and ventrally part of a bony crypt for the adult canine is preserved.
'Adult canine in crypt exhibiting partially formed crown; no root formation.
'Tooth has been lost postmortem, but root socket or sockets give indications of its developmental status.
7Small pieces of dP3 mesiobuccal and distolingual roots are preserved.
'Specimen preserves right perminent canine in crypt; crypt for developing right canine partly preserved. Small sockets
for right and left (?I deciduous incisors are present; no space for permanent incisors.
PARAPITHECID DENTAL ERUPTION
incisors. No bony crypts are visible radiographically, implying that no permanent
teeth have developed to a recognizable degree at this stage. Nothing can be learned
from this specimen about the state of the
teeth distal to dP3.
365
In YPM 20934, one of the roots of dP2 and
both roots of dP3 and dP4 are visible, MI is
fully erupted, and Mz is above the alveolar
margin but not in occlusion; M3 has not developed to the bell stage (Fig. IB). A broken
crypt for a developing C is visible as are, on
Fig. 1. Apidium phiomense. Radiographs of mandibles of juvenile specimens, all from Quarry
I, Upper Fossil Wood zone, Jebel Qatrani Formation, Fayum Province Egypt. A, YPM 23959;
B, YPM 20934; C, YPM 23958; D, DPC 1050; E, YPM 23991. Abbreviations: Standard dental
terminology identifies each tooth or tooth germ; r.s., root socket. Apporximately x2.5.
366
R.F. KAY AND E.L. SIMONS
Fig. 2. Apidium phiomense (A and B) and A. moustafai (C). Radiographs of juvenile specimens. A, AMNH 13370; B, DPC 1102; C, YPM 20911. Abbreviations as in Figure 1. Approximately x2.5.
radiographic examination, those for Pa, P3,
and P4, each containing a tooth-bud. P2 is
further developed than either P3 or P4: its
root is partially formed, whereas P3 and P4
are crowns without roots. YPM 23960,23996,
and 23997, and DPC 1043 and 2942 show a
comparable degree of development in preserved parts to YPM 20934 except in having
an M3 in its crypt. Three of these specimens
show P2, with its root partly formed, close to
the alveolar margin whereas roots of P3 and
P4 are not yet formed and they are further
from the alveolar margin. Two specimens
show C in its crypt with a partially formed
crown.
YPM 23958 has advanced further in development (Fig. 1C). MI and M2 are fully developed and erupted, while dC-dP4 remained in
occlusion. The crown of dP3 is much more
heavily worn than that of dP4, suggesting
dP3 erupted before dP4. YPM 24595 and
24507 show a similar stage of development
to that of YPM 23958 in preserved parts.
In DPC 1050 and YPM 23991 dp2 has been
shed and P2 is fully erupted. In each, the root
structure of the erupting P4 is more fully
PARAPITHECID DENTAL ERUPTION
367
Fig. 3. Apidium phiomense. Scanning electron micrograph (SEMI of anterior dentition of
DPC 1089 (Quarry I) viewed from a medial and slightly posterior perspective. Approximately
x 10.SEM is of original specimen.
developed than that of P3 (Figs. lD, E). In
YPM 23991, P4 is more fully erupted than P3
whereas in DPC 1050 the two appear equally
b u t incompletely) erupted. AMNH 11370 has
advanced somewhat further (Fig. 2A); dP4 is
shed and P4 root formation is far advanced
and the tooth is nearly in occlusion, while M3
has less well-developed roots and is less fully
erupted. YPM 23948 and 23952 show a comparable state of devleopment to AMNH
11370.
DPC 1102 is a virtually dentally adult specimen with P2-M3 fully erupted and in occlusion (Fig. 2B); however, in this presumed female (Fleagle et al., 19801, C is not fully in
occlusion.
From these specimens of Apidium phi@
mense, the following pattern of eruption of
the canine and postcanine teeth may be deduced (the sequence of eruption is from left
to right; specimens within parentheses have
a n uncertain eruption sequence):
dP3, dP4, M1, pz, p4, (P3, M3)1 c.
From the available specimens, it appears that
the time of eruption of P4, P3, and M3 are so
similar as to suggest the possibility that
there is variability in this part of the eruptive sequence.
As to the sequence of calcification of the
tooth buds in Apidium phiomense, little can
be said with certainty. However, if it is assumed that the rate of crown calcification is
similar or nearly constant for all tooth buds
(a dubious assumption, a t best), projecting
backward from early developmental stages,
it appears the sequence of initial calcification
of the adult teeth was:
Mi, Ma, P2, (P3, P4), C, M3.
This is more or less the same as (although
less certain than) the eruption sequence with
the exception that M3 apparently began to
calcify after C (as shown by YPM 209341, but
erupted before it (as in DPC 1102).
On the basis of the mixed evidence of the
amount of calcification of the tooth crown,
the state of root formation and the eruption
of the tooth, Conroy et al. (1975)give a developmental (equals eruption) in Apidium phi@
mense of M1, Mz, P2, M3, Pq, P3, C. This is
substantially in agreement with the present
findings based on a larger sample except in
the timing of eruption of M3. The presently
available series suggest M3 erupts ufcer P4,
not before it. For example, AMNH 11370 has
P4 almost fully erupted with very slight wear
on the tip of its protoconid, while M3 has
368
R.F. KAY AND E.L. SIMONS
barely erupted above the level of the alveolar
bone. Furthermore, the roots of P4 are almost
completely developed whereas those of M3
are much less completely formed. Whether
M3 erupts before or after P3 is uncertain on
the basis of the available material. Data reviewed above as to the developmental (calcification) sequence imply that M3 may develop
later in the sequence than it erupts. In fact,
M3 may be the last tooth in the lower jaw to
begin calcification, not fourth from the last,
as Conroy et al. (1975) state.
Development of upper teeth
Two subadult maxillae of Apidium phi@
mense are known. DPC 3060 from quarry M
has dP2-dp in occlusion and exhibiting very
little wear. No wear facet is visible on dP4
suggesting M' was not in occlusion. A grove
mesial to dP2 oints to the presence of dC. C,
P2, P3, and Pf crowns are partially formed.
Based on their positions relative to the alveolar margin, it may be inferred that P2 would
have been first to erupt, then p.C and P3
would have erupted later. YPM 23962 is a
ri ht maxillary fragment with dP3, d p , and
. occlusion. is in the bell stage; also a
M8 in
partial crypt for P3 is preserved. Based on
these two specimens a sequence of eruption
of the permanent maxillary teeth may have
been (P2, MI), p,(P3,C).
Dental formula
A permanent dental formula of 2 . 1 . 3 * 3/
2 - 1 . 3 . 3 has been proposed for A p i d i u m p h i e
mense (Simons, 1971, 1972). More specimens
(especially DPC 1089 from Quarry I) (Fig. 3)
confirm the lower incisor formula: Apidium
has two incisors in each lower jaw quadrant
with 11 having a much smaller caliber than
12. No specimen has yet been recovered which
preserves upper incisors in combination with
other teeth to confirm the upper anterior
dental formula. A number of isolated upper
incisors appear to be attributable to this species, however, on the basis of size and general
structural similarity to those of other
anthropoids.
On the basis of material described above,
the deciduous dental formula of Apidium
phiomense is ?.1-3/2.1.3.
APZDIUM MOUSTAFAI (FIG. 2C)
YPM 20911 is the only mandible of A.
moustafai not a full adult dentally. Left PaM2 are fully erupted. Broken root sockets for
M3 remain, but do not clarify its state of
eruption. The canine is present, but unerupted. Thus C was either the last or next to
the last (before M3) of the cheek teeth to
erupt, as in A. phiomense.
A maxillary fragment YPM 20922 preserves dP3, d p and M' in occlusion. Developing tooth buds for the permanent teeth
were not observed radiographically.
PARAPITHECUS GRANGER1 (FIGS. 4 , 5 , 6 )
Development of the lower teeth
Five specimens (all from quarry I) have
deciduous lower teeth and/or partially
erupted permanent ones. The state of development is detailed in Table 2 based on visual
and radiographic examination, as outlined
above. Based on the state of development
pattern of wear and communality of preserved parts, each specimen came from a different individual.
The youngest individual represented is
YPM 23796, a right mandible showing the
state of development a t all tooth loci on the
right side and that of the anterior dentition
of the left side. In this specimen, dP, had
presumably been shed and P2 was fully
erupted, as judged from the state of the P2
root socket. dP3 and dP4 are in occlusion,
each being moderately worn. Radiographs
reveal that P3 and P4 are in their crypts but
have begun neither root formation nor eruption (Fig. 4A). MI and M2 are in occlusion;
M3 is in its crypt. A groove for the buccal
edge of the root of right dC is visible with
right C beneath it with crown formation essentially complete. The complete mesial surface of the crypt for left C is preserved. This
structure is closely pressed against the crypt
for right C, the tooth germ of which may be
seen through a narrow window in the bone
(Fig. 5A). This window appears to be a real
feature of the bony conformation, not a product of postmortem breakage; a similar window is clearly visible also in DPC 2399 as
noted below. The alveolar margin of the symphysis of YPM 23796 is preserved lingually
but broken away labially. Visible on this lingual alveolar region are portions of two small
incisor crypts disposed symmetrically about
the midline. Thus, at this stage of development there are indications of only a single
incisor in each lower jaw quadrant.
DPC 2399 confirms the interpretations
made about YPM 23796. This specimen
shows a slightly later stage of development
in which P4 was partially erupted and has
slight tip wear; neither P3 nor P2 are pre-
369
PARAPITHECID DENTAL ERUPTION
Fig. 4. Parapithecus grangeri. Radiographs of juvenile specimens. A, YPM 23796; B, DPC
2399. Abbreviations a s in Figure 1.Approximately ~ 2 . 5 .
TABLE 2. Deuelopmental data for Parapithecus grangeri mandibular dentitions
Specimen
Tooth locus
No.
dClC
YPM 23796'
DPC 1114
DPC 1118
DPC 2399
DPC 3110
D2B
d6B4
D6B4
D'IB
-
dPzlPz
EID'
EID'
EID'
-
dP3IP3
dP4IP4
DZB
DG/B
D6/B4
-1c26
DZB
D6/B
D2B
EIC3
-
-
M1
pz
M3
D2
Di
D6
B
D1
B
B
D2
D1
D1
D2
D6
D1
-
cz
Developmental stages: A, tooth not developed; B, tooth in crypt; C , tooth partly erupted; C,, some movement; C2, cusp
tips at or near alveolar margin: Cs, some tip wear; D, tooth fully erupted D,, little wear; DZ,enamel perforated in
several places; D3,much of tooth surface shows wear; E, tooth reabsorbed and/or shed. For an explanation of superscript
notation, see footnotes to Table 1.
served, but their sockets suggest they were
fully or almost fully erupted (Fig. 4B).Left C
remains in its crypt without detectable root
formation; dC was presumably in occlusion,
but has been broken away. Grooves in lingual alveolar bone of the symphysis may be
remnants of sockets for single incisors in each
lower jaw quadrant. The mesial part of the
socket for right C is intact a window in the
alveolar bone links the sockets of left and
right C.
In summary, available evidence indicates
that eruption sequence for the lower cheek
teeth of Parapithecus grangeri may have been
the same as that in Apidium phiomense: Pa,
MI, and M2 all erupted before P3 and Pq; C
and M 3 were the last of the cheek teeth to
erupt.
370
R.F. KAY AND E.L. SIMONS
Fig. 5. Purupithecus grungeri, YPM 23796. A) Stereo
SEM of symphyseal region of the right side viewed from
a medial and anterosuperior perspective. Approximately
X 5 . B) Same specimen viewed superiorly. Approximately x 10. Abbreviations: C, right canine in crypt and
crypt for left canine; dP,, deciduous third premolar; I,
sockets for right and left (?) deciduous incisors; n.f., nutrient foramen for canine; Pz, socket for second lower
premolar; s., midline (symphysis) of mandible; s.k., symphyseal keel in midline; w, window in bone between
crypts for right and left canines. SEMs are of original
specimen.
Development of the upper teeth
DPC 1123, a maxilla of Parapithecus grangeri, contains a deciduous p.In this specimen M1 is fully erupted and M2 erupting
with roots incompletely formed. P3 and P
are still in their crypts; the state of dP3 cannot be determined.
Dental formula
From juvenile specimens described above,
teeth or tooth sockets confirm the presence
in l? grangeri of one (presumably) deciduous
lower incisor, as well as a deciduous canine
and a t least two (probably three) deciduous
premolars. A number of mandibles, DPC
PARAPITHECID DENTAL ERUPTION
Fig. 6. Purupithecus grangeri, DPC 3135. A) Stereo
SEM of symphyseal region viewed from a n anterior and
lateral perspective. Approximately x5. B) Same specimen viewed occlusally. Approximately x 10. Note break
371
which runs through the socket for right C. Abbreviations: C, canine sockets; Pz, sockets for right and left
canines; Ps, lower third premolar; s, symphysis of mandible. SEMs a r e of original specimen.
2376, DPC 2807, and DPC 3135 show that cation of DPC 3135 as I? grangeri is definite
this species had a permanent canine, three judging from the overall size of the cheek
permanent premolars and three molars. teeth, the relatively small size of the M3, and
However, newly recognized specimens show the shallowness of the jaw beneath the mothat adult Parapithecus grangeri had no lars. These and other proportional similarilower incisors. The configuration of this part ties are nearly identical with undoubted I?
of the jaw is especially clear from DPC 3135, grangeri specimens such as DPC 2376 and
from quarry I (Fig. 6) a nearly complete man- DPC 2807 which between them retain C-M3
dible with right and left P3-M3 and all sock- in good condition. In DPC 3135, anterior to
ets for teeth anterior to P3. The enamel is each P3 is a smaller socket for Pz and a large
heavily eroded on all teeth but the identifi- canine socket. The right canine socket is bro-
372
R.F. KAY AND E.L. SIMONS
ken but the irregular edges of the two parts sors compare most closely with 11s of P r e
fit together precisely without any lost bone; pliopithecus chirobates from the same quarry
each canine socket is missing some alveolar Ce., with those of DPC 1069).
The permanent upper cheek-tooth formula
bone labially, lingually and distally. However, the mesial margins are extremely well of €? grangeri was 1.3.3, as shown by DPC
preserved and jointly form a midline of the 2385 which has C-M3. Upper incisors have
mandible. As Figure 6 clearly shows, there not been found in definite association with €?
is no space for lower incisor sockets in the grangeri cheek teeth. Only two upper decisymphysis of this adult specimen. Based on duous premolars have so far been docuthe currently available specimens it is likely mented either by crowns or root remnants.
that either: 1) a single deciduous incisor
DISCUSSION
erupted and persisted in the jaw until the
In their analysis of the dental eruption seeruption of C and then was lost; or 2) a single
deciduous incisor erupted, and was replaced quences of parapithecids, Conroy et al. (1975)
by a single permanent one; then this perma- stress that in parapithecids 1)the order of
nent incisor is lost with eruption of C. If we eruption of the premolars in the sequence of
opt for the first choice, the lower dental for- Pz, Pq, P3 (as confirmed by this study) was a
primitive holdover from the ancestor of primula was:
mates of modern aspect, and 2) the late development and eruption of the lower canine
deciduous: 1* 1* 3
might be a shared derived (or synapoadult: 0.1.3.3.
morphic) feature of Anthropoidea. With reIn the event the second option proves corect, spect to the first of these conclusions, we
the permanent formula would be 1 . 1* 3 3. In would comment that the evidence for the Pz,
either case, lower incisors are not retained in P4, P3 having been the ancestral sequence
the adult.
for all primates of modern is open to doubt.
Some question might be raised about our This sequence of dental eruption is reported
identification of the large anterior tooth of among most living strepsirhines with three
Parapithecus grangeri being a canine, not an premolars (exceptions: Lemur catta, Lepileenlarged incisor. Two reasons may be cited muq and Hapalemur), and in Tarsius
for our interpretation. First, the large tooth (Schwartz, 1974). However, although it is
we interpreted as being C is the last or nearly seen on occasion in New World monkeys, it
the last tooth to erupt as are canines typi- is not as widespread a s a sequence where P4
cally in Anthropoidea (Schultz, 1935; Byrd, is the first tooth to erupt fully (Byrd, 1979).
1979). In contrast, even in those anthropoid Observation of Paris material of Adapis conspecies with enlarged incisors like Callithrix, firm Stehlin’s (1912) conclusion that P4 was
the incisors are among the first teeth to erupt the first tooth to erupt in this Eocene ada(Hershkovitz, 1977; Byrd, 1979). Second, pine, whereas P2 is first to erupt in the limthere is a striking morphological similarity ited material of the notharctine Notharctus
between this lower tooth in Parapithecus reported by Gregory (1920a).Thus, considergrangeri, as documented by serveral speci- able variability exists among closely related
mens, and the canines of Apidium spp. and species, and even if this is ignored, communParapithecus fi-aasi. For these reasons we re- ality by no means confirms that Pz, P4, P3
gard the possibility that this tooth is a n inci- was the pattern of eruption found in the
sor a s extremely remote.
ancestor of all primates of modern aspect.
Special mention should be made about Moreover, variability in the premolar erupYPM 23054. This is a composite specimen of tion sequence is extremely common within
Parapithecus grangeri from quarry I, figured some species. In a sample of five Ccbus albiby Simons (1971) and Szalay and Delson f r o m observed by one of us (R.F.K.), P2 was
(1979)composed of a mandible with right P4- first to erupt in one animal and P3 was first
M3 and sockets for right P2 and C with a to erupt in three animals; in one animal all
symphysis constructed of plaster holding two three premolars erupted nearly simultaneisolated incisors, a right canine, and a right ously! The occurrence of such variation casts
Pa, all collected in 1966. Collection of mate- doubt as to the phyletic valence of these tendrial since then confirms that the isolated can- encies and the certainty with which one
ine is that of a €? grangeri, but suggests that might be able to determine which was the
the “Pz” is actually a P3. The isolated inci- ancestral state for any group.
373
PARAPITHECID DENTAL ERUPTION
The late eruption of the lower canines of
parapithecids, the second point emphasized
by Conroy et al. (1975), is confirmed by additional material; the lower canine of Apidium
is either the last tooth (or the penultimate
one before M3) to erupt. This is a resemblance to extant anthropoids as Conroy et al.
noted. Recent studies by Byrd (1979)confirm
that late canine eruption is ubiquitous among
New World monkeys; it is found in most Old
World monkeys and hominoids (except Homo,
and Nasalis; Schultz, 1935). It is not seen
among nonanthropoids: tarsiers or living
strepsirhines (Schwartz, 1974). However, the
late eruption of the lower canines occurs in
the Eocene adapids Notharctus and Adapis
(Gregory, 1920a; Stehlin, 1912) although not
in the omomyid Absarokius (Gazin, 1958).
This raises the possibility that late eruption
of the lower canines is a shared-derived resemblance between adapines and anthropoids.
The new material also shows that (contra
Conry et al., 1975) M3 was very late to erupt
in Apidium phiomense, being the next-to-last
(before the canine) and virtually simultaneous with P3. The late eruption of M3 may be
another derived feature parapithecids share
with extant anthropoids. In virtually all extant Old World and most New World monkeys with three molars M3 comes in after all
the deciduous premolars have been replaced
(exceptions:Aotus, Pithecia) whereas it erupts
before all deciduous premolars are replaced
in Tarsius, all extant strepsirhines (except
indriids), as well as Eocene adapines NCF
tharctus and Adapis and the omomyid A bsarokius (vide Byrd, 1979; Gazin, 1958;
Gregory, 1920a; Schultz, 1935; Stehlin, 1912).
Perhaps the most surprising finding of this
study is the demonstration that Pczrczpithecus
grangeri adults had no lower incisors, and
juveniles had just one incisor in each lower
quadrant. This reopens the question of the
dental formula of Parapithecus fraasi. I?
fraasi, described by Schlosser (1911),is based
on a mandible collected by Richard Markgraf
in 1907 (Gingerich, 1978), separated into two
parts at the midline and damaged postmortem by the loss of one cheek-tooth (now
known to have been the right Pz). It was
generally agreed by early workers that the
damage at the symphysis did not include the
loss of any teeth, and it was stated that there
were eight teeth in each jaw quadrant.
Schlosser (1911)could not decide whether the
second tooth from the symphysis was a n in-
cisor or a canine and so whether the dental
formula was 1.1 3 3 a s in living tarsiers or
2 * 1- 2 . 3 as in present-day catarrhines.
Schwalbe (1915), Gregory (1916, 1920b) and
Werth (1918) opted for the latter interpretation, as did Kalin (1961), after a restudy of
this specimen. He also concluded that the
mandibular symphysis was unfused during
life as in primitive primates, not fused as in
anthropoids.
With recovery of new specimens of Apidium, Simons (1963, 1971, 1972) was able to
show that some parapithecids had a dental
formula 2 . 1 * 3 * 3. By analogy, he suggested
that Parapithecus fraasi and I? grangeri
probably also had a formula of 2-1.3.3. He
interpreted Schlosser’s specimens of P fraasi
as having lost a n incisor from each lower jaw
quadrant when the mandibular symphysis,
fused in life, was damaged postmortem.
The new specimens of Parapithecus grangeri described here show its dental formula
to be 0.1.3.3 in the adult. A single lower
incisor in each jaw ramus was present in
juveniles before the permanent canines
erupted. As those are known only from their
alveoli, whether they represent deciduous incisors or their replacement teeth cannot yet
be determined. The incisor reduction in Parapithecus grangeri makes more plausible
Schlosser’s (1911) suggested dental formula
of 1.1.3.3 for I? fraasi. There is no longer
any reason to believe that teeth were lost
from this specimen postmortem, either by
natural processes or when collected. If so, I?
fraasi, with a single pair of lower incisors
might be viewed as a n “intermediate” form
between Parapithecus grangeri, with no incisors in the adult, and a primitive parapithecid with a pair of incisors in each quadrant
of the lower jaw, a s in Apidium.
One aspect of the incisors of Parapithecus
grangeri derserves additional mention. These
teeth have much lighter colored enamel than
the other teeth in the jaw. Such a situation
is frequently, although not always, a characteristic of deciduous teeth, raising the possibility that the incisors of Parapithecus fraasi
are of the deciduous complement persisting
into the adult. Only the recovery of more
anterior teeth of Parapithecus fraasi will resolve this possibility.
In view of the difference in dental formulae
between adults of Parapithecus fraasi, in
which at least one incisor is retained, and
those of Parapithecus grangeri which have
no incisors, Gingerich’s (1978) suggestion
- -
374
R.F. KAY AND E.L. SIMONS
that the latter be removed to its own genus
Simonsius now deserves additional consideration. We reserve our opinion pending a reassessment now in preparation of other
structural details of the two species. On the
other hand, we disagree with his proposed
synonomy of Parapithecus fraasi with Apidium phiomense. Gingerich dismisses three
obvious differences between the two as being
of the sort found as common variants within
living species and claims that the type specimen of the former lies well within the range
of variation to be expected in a sample of the
latter. The three differences he dismisses are
that 1)the third molar of the type specimen
of A. phiomense is relatively much larger
than that of l? fraasi, 2) the type of A. phi@
mense has a well-developed centroconid on
the molars whereas I? fraasi lacks it, and 3)
the teeth of the type of A. phiomense are
unworn whereas those of I? fraasi are moderately worn. Now that many specimens of
A . phiomense are known, it becomes possible
to test and reject this claim as well as to add
other differences between the two species.
Through the 1981 field season, 33 specimens of Apidium phiomense were collected
for which both M 2 and M3 lengths can be
estimated. The mean of the ratio of M2:M3 is
0.87 with a standard deviation of 0.035. The
same ratio for the type of l? fraasi is 0.95,
outside the 95% confidence interval for A.
phiomense.
In available samples of unworn 26 Mzs and
22 unworn M3s of A. phiomense collected
through the 1981 field season, all possess
centroconids. Therefore, the type of l? fraasi
differs uniquely from A. phiomense in having
no M2-3 centroconids.
Of course tooth wear, by itself, as Gingerich rightly states, is of no relevance to a
taxonomic determination. However, interestingly Apidium phiomense molars wear flat
and because of extremely thick enamel most
crown features are obliterated before the
enamel is performated. In ?? fraasi the enamel is much thinner and performated a t a n
early stage in the wear. Failure to recognize
this difference might lead to a n eroneous conclusion that some A. phiomense lack centroconids when this feature was simply removed
owing to a n advanced state of wear.
Another distinct difference is that Parapithecus fraasi seems to have possessed a reduced number of incisors whereas Apidium
phiomense certainly had two in each low jaw
quadrant.
The conclusion reached on examination of
these many new specimens of A . phiomense
is that this species should continue to be regarded as distinct from Parapithecus fraasi
at both the specific and generic levels.
It is important to recognize that although
the reduced anterior dental formula of Parapithecus is Tarsier-like, as noted originally
by Schlosser (1911), incisor loss was clearly
evolved in parallel in the two groups because
Apidium, a close relative of Parapithecus,
still preserves its full complement of incisors.
Also, it becomes clear that Parapithecus
grangeri can not have been directly ancestral
to living Old World monkeys, a view advocated by each of us in the past.
ACKNOWLEDGMENTS
This research was supported by NSF grant
BNS-81-14925and BNS-80-16206and Smithsonian foreign Currency grants 70869600
and 809479. P. Chatrath prepared some of
the specimens. We also thank John Fleagle
and Ross MacPhee for helpful comments. Eric
Effmann helped with the radiography.
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