Dental formulae and dental eruption patterns in parapithecidae (primates Anthropoidea).код для вставкиСкачать
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 18.104.22.168 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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