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Kruska, Kiel Z39.48-1992 (PermanenceofPaper). P. Lüps, Bern Printed in Germany ©2001 Urban & Fischer Verlag Fordetailedjournalinformation seeourhome page: A. Wöhrmann-Repenning, Kassel http://www.urbanfischer.de/journals/mammbiol Mamm. bioi. 66(2001)193-203 |Är Mammalian Biology © Urban & FischerVerlag H^SP http://www.urbanfischer.de/journals/mammbiol Zeitschriftfür Säugetierkunde Original investigation Supernumerary molars in neotropical Opossums (Didelphimorphia, Didelphidae) By D. AstüadeMoraes, B. Lemos, and R. Cerqueira Departamento de Zoologia, Universidade de Säo PauLo, Departamento de Genetica, Um'versidade FederaL do Rio deJaneiro, and Departamentode Ecologia, Universidade FederaLdo RiodeJaneiro, ReceiptofMs. 17. 05. 2000 AcceptanceofMs. 28.09. 2000 Abstract Dental abnormatives, such as the occurrence of extra teeth, are recurrently found in many groups ofmammals. Supernumeray molars werefound in Didetphis aurita, D. albiventris, D. marsupialis, Phi- tanderandersoni, P.frenata, P. opossum, Chironectes minimus, and Coluromysphiiander. Frequencies ofoccurrence ofsupernumeraryteeth in these marsupialspecies remained within a ränge similarto that found in other species. Four hypotheses are proposed and discussed to explain the origin of these teeth: appearance ofextra teeth due to excessive developmentin size ofthe skull, reappear- ance ofan atavistic condition, retention ofthethird deciduous premolaratthe eruption ofthe permanent premolar, or some sort ofontogenetic disturbance that lead to the duplication of a tooth germ. The first hypothesis is discarded as allindividuals have normal sizes forthe species. No evidence in the marsupial fossil record supports the second. The morphology of the teeth observed does notsupportthethird, as allteeth are apparently permanent (exceptforone specimen). Finally itis hard to find evidence against orin favourofthe fourth, as there is no information available of the development ofthe museum specimens observed. Key words: Marsupiais, abnormalities, dentition, Neotropics Introduction Thestudyofabnormalitiescanbeparticularly Mammal dental abnormalities have long interestingforthose involvedindevelopmen- been reported, and include teeth specific tal genetics and morphological evolution, malformations (e.g. Long and Long 1965; providing useful data for medical, evolution- Feldhamer and Stober 1993), size reduc- ary, and taxonomic studies. For instance, by tion or missing of teeth (e.g. Mech et al. focusing on abnormalities one can assess the 1970; Drehmer and Ferigolo 1996), or potentialities for the rise of new variant supernumerary teeth (e.g. Krutzsch 1953; morphologies. Morphological shifts occur Steele and Parama 1979; Kvam 1985; with the rise of such deviant morphologies Drehmer and Ferigolo 1996). The latter anditsspreadingthroughthetaxon.Thus,ab- corresponds to the occurrence of more normalities, as highly deviant morphologies, teeth than those expected from the species couldinitiate suchmorphologicalshifts. normal dental formula. Such phenomenon 1616-5047/01/66/04-193 $15.00/0. 194 D. ASTÜADEMORAESetal. has been described foreutherian families as was calculated based on adult specimens diverse as e.g. Mustelidae (Long and Long with four molars erupted, as the number of 1965), Otariidae (Drehmer and Ferigolo individuals presenting any extra tooth di- 1996), Felidae (Kvam 1985), Canidae (van vided by the total number ofspecimens ex- Valen 1964), Cervidae (Fowle and Pass- amined for that species. The frequency of more 1948; Pekelharing 1968; Steele and supernumerary teeth is 0.7% (1/141) in Parama 1979; Mech et al. 1970), Soricidae C. minimus; 1.2% (1/82) in C.philander; (Hooper 1946), Dipodidae (Krutzch 0.5% (3/655) in D. albiventris; 0.3% (1/337) 1953), and Sciuridae (Goodwin 1998). in D. aurita; 1.0% (9/872) in D. marsupialis; Within the marsupial family Didelphidae 2.8% (1/36) in R andersoni; 0.8% (2/244) supernumerary teeth have been reported in P. frenata; and 0.3% (2/767) in P. opos- forthe genusDidelphis (Allen 1901; Taka- sum. hashi 1974) only and recently forPhilander (Hershkovitz 1997). The aim of this study Tooth morphologyand position therefore is to investigate the Situation for South American marsupials in more detail. The location of the supernumerary tooth found is reportedin table 1. Supernumerary teeth were found at all molar rows; how- Material and methods ever, they were more frequent at the Upper rows. The following species were investigated: Calur- omys philander (Linnaeus, 1758), Chironectes minimus(Zimmermann, 1780),Didelphisalbiven- Caluromysphilander trisLund, 1840,D. auritaWied-Neuwied, 1826,D. The only specimen (MZUSP 11591) found marsupialis Linnaeus, 1758, Philander andersoni (Osgood, 1913), P. frenata (Olfers, 1818), and P. with an extra tooth presents it at the end opossum (Linnaeus, 1758), from specimens de- of the right inferior molar series (Fig. 1). It positedinthefollowingcollections:MuseuNacio- is slightly smaller than the M4. Cuspids are nal, Rio de Janeiro (MN); Departamento de Zo- distinguishable with the protoconid exces- ologia, Universidade Federal de Minas Gerais sively developed in comparisonto the para- (DZUFMG); Museu de Zoologia, Universidade conid and metaconid that are reduced. The de Säo Paulo (MZUSP); American Museum of talonid is slightly reduced, and is divided NaturalHistory (AMNH); FieldMuseum ofNat- antero-posteriorly by a crest, not present in ural History (FMNH); National Museum ofNat- the normal teeth, that creates two basins ural History (NMNH); and Laboratörio de Ver- and makes the identification of the talonid tebrados, Universidade Federal do Rio de Janeiro (MC). Collection numbers, sexes and lo- cusps more difficult. This tooth is aligned calities for specimens found with supernumerary with the molar series in occlusal view, but molars are listedintable 1. its crown is slightly tilted to the lingual side. Unless otherwise specified tooth morphology no- menclature follows Reig et al. (1987). Notations in super- or subscript refer to specific (upper or Chironectesminimus luosweedr,inretsopoetchtifvoelrym)ultaoeotnhomreonwcsl,atausretra(de.itgi.onMal4l)y, Tmohlearonfloyr otchicsursrpeenccieesof(MaZUsuSpPern1u65m4e5r)ariys but when no specific row is meant, we chose not an extra molar erupting behind the right touse super- orsubscript (e.g. M4). M4 (Fig. 2). The tooth is not fully erupted (only the protoconid, and the tips of the metaconid and entoconid emerge from the Results bone), but its crown pattern is clearly visible and identifiable with conids and cristids Frequencyofoccurrence M pattern identical to the 4. The tooth is The frequency ofsupernumerarymolars oc- clumped, as there is no Space available for currence in each of the investigated species it in the mandibular ramus and is erupting Supernumerary molarsin neotropicalopossums 195 Table 1. Individuais observed with supernumeraryteeth, with respectivespecies, museum number, sex, locality oforiginand location ofsupernumerarymolars. Legend: M: Male; F: Female; UL: UpperLeftrow; UR: Upperright row; LL: Lowerleftrow; LR: Lowerrightrow. Museumacronymsasintext Species Museum Number Sex Locality Locationofsuper numerarymolar Caluromysphilander MZUSP11591 M Fordländia, Parä, Brasil 1UlIR\ Chironectesminimus MZUSP16545 F Cametä, Parä, Brasil LR Didelphisalbiventris AMNH 63852 M Utcuyacu,Junin, Peru L|_ LR Didelphisalbiventris DZUFMG 120 M Santa Luzia, MinasGerais, Brasil HR Didelphisalbiventris MN 22250 F Brasilia, Distrito Federal, Brasil UMlL 1IR LL LR Didelphisaurita AMNH 133034 M ParaibadoSul, RiodeJaneiro, Brasil IUIIL HUlR\ Didelphismarsupialis AMNH 33243 M Esmeraldas, Ecuador UR Didelphismarsupialis AMNH 93978 F Nortedo RioAmazonas, Faro, Parä, LR Brasil Didelphismarsupialis AMNH 95345 M RioTapajös,IgarapeAmorim, Parä, LR Brasil Didelphismarsupialis AMNH 95361 M RioTapajös, Inajatuba, Parä, Brasil UR UlUcLfJI1/_>lilUlbUfJIULlj AMNH ?f)Q17Q M RDCoIni11, DRnUlLiI\V/il3a UL UR LL LR Didelphismarsupialis USNM 280966 M Villanueva, Colombia UR Didelphismarsupialis USNM 51092 M RioTapajös, Caxiricatuba, Parä, Brasil UR LR Didelphismarsupialis USNM 545457 F Beiern, Parä, Brasil UR Didelphismarsupialis FMNH 22199 M SierradeMerida, Merida,Venezuela UL Philanderandersoni AMNH 72017 F RioCuraray, Loreto, Peru UL Philanderfrenata MC267 M Maricä, RiodeJaneiro, Brasil UL UR Philanderfrenata MN 5769 M SantaTeresa, EspiritoSanto, Brasil UL UR Philanderopossum AMNH 34373 ? Bagadö, Chocö, Colombia UL UR Philanderopossum USNM337643 M ElRecreo,Zelaya, Nicaragua UL UR with its crown tilted about 45 degrees lin- is smaller than the M4 and similar in shape, gual and anteriorly in comparison to the re- yet with much reduced stylar cusp C, and maining molars. slightly compressed, so that the stylar cusp E (metastyle) is closer to the paracone than in the M4 All remaining cusps are clearly Didelphisalbiventris . identifiable. It is also slightly rotated coun- Specimen DZUFMG 120 presents a Single ter-clockwise. Its crown lies beneath the oc- supernumerary molar, erupted behind the clusal plane ofthe rest ofthe series but oc- rightM4 (Fig. 3). Itis asmall tooth (approx. cludes with the extra molar of the inferior o1/v3alofcrtohwen,sizweitohf tthweoncoursmpaslcMon4n),ecwtietdh bayn sseirdieesi.sTihdeenteixctarlaitnoosthhapoenttohethreigMht4s,uapnerdioorf cristae. Its reduced size and abnormal about half its size. Unlike the tooth pre- wchraotwnthsehsaepceusmpaskaensdictridsitffaiecualrteteoquiidveanlteinfty vairoeussliymildaersctroibtehde,Mo4r,ieanntdatiaopnartanfdromcustphse to in normal teeth. The tooth is very tight, size difference, there is no deformation or hasintdhetrheeisMn4o. Tphlaececrfoorwnitoofntthhies mtaoxoitlhlai,s baep-- obtehneeratshhatphee odcicffleurseanlcep.laIntes cofrotwhne Mals4o, alineds proximately in the same occlusal plane as apparently does not occlude. The left infer- normal molars, but it does not occlude with ior eMxtra tooth (Fig.4) is overall similar to any inferiorMtNooth. the 4M, especially the trigonid is identical Specimen 22250 possesses one super- to the 4 trigonid, with all cusps identifi- numerary molar at the end of each series. able. In the talonid, however, the hypoco- The extra tooth on the left superior series nulid is closer to the hypoconid, giving the 196 D. ASTÜADEMORAES etal. whole talonid a more elongated or triangu- Didetphis aun'ta lär shape. Finally, the supernumerary molar AMNH Specimen 133034 possesses one on the right mandible (Fig. 5) also presents M supernumerary molar in each side of the a trigonid identical to the 4 trigonid, but superior row. Both extra teeth have a mo- with a slightly different talonid, with a hy- poconulid somewhat farther from the trigo- lariform shape but are slightly reduced. The extra tooth on the right superior series nid than in the latter. is posteriorly directed, probably due to the lack of Space in the row, and is not at the oclusal plane of the remaining teeth. Its cusps are present and distinguishable with a crown pattern resembling a normal M4 . The other extra tooth at the left superior series is not at the occlusal plane of the remaining row and its cusps, although distinguishable, do not resemble a normal M4 pattern. Fig. 2. Right inferior molar series (M2-M4) of Chiro- Fig. 1. Rightinferiormolarseries ofCaluromysphitan- nectesminimus (MZUSP 16545), with a supernumerary der (MZUSP 11591 ), with a supernumerary molar (ar- molar (arrow), viewed from the occlusal plane ofthe row). Occlusal view. Protoconid (Prd), paraconid extra tooth. Protoconid (Prd), paraconid (Päd), meta- (Päd), metaconid (Med). conid (Med), entoconid (End), hypoconid (Hyd). Supernumerary molarsin neotropicalopossums 197 D. marsupiab's merary tooth is smaller than the M4. Some AMNH cusps are discernible, as well as what ap- Specimen 93978 possesses one ex- pears to be the centrocrista. Protocone, tra tooth on each side of the superior rows. paracone and metacone are identifiable, Both are reduced but with a molariform but the cusp present on the opposite side shape. The extra teeth at the righthas some cusps visible (but hardly identifiable), and a crista, which is apparently the centrocrista, oriented with the antero-posterior axis of the skull. Philanderfrenata MC Specimen 267 presents one extra molar on each side, at the end ofthe Upper molar series. On the left side (Fig. 6), the supernu- Hyld Fig.4. LeftinferiormolarseriesofDideiphisalbiventris Fig.3. Right superior molar series of Dideiphis albi- (MN 22250), with a supernumerary molar (arrow). Oc- ventn's(DZUFMG 120),withasupernumerarymolar(ar- clusalview. Entoconid (End), hypoconid (Hyd), hypo- row). Occlusalview. conulid (Hyld). 198 D. ASTÜADEMoraesetal. ofthe centrocrista cannot be identified. Ac- Philander, and the M4 resembles a normal tMua4llays,dtehsiscreixbterdabtyooHtehrsrhekseomvbiltezs(a19n9o7)rmfaolr mMo3r:eOndeftohremerdi,ghtsosmideewhtahte eoxvtarlalytosohtahpeids with some cusps visible (but hardly identifiable), and a partially formed crista (apparently the centrocrista, oriented with the antero-posterior axis of the skull). Unlike on the left side, the right tooth shows some degree ofwear on the cusps and outer cristae. In both cases teeth are partially clut- tered onthe M4 andcrowns are onadiffer- , ent occlusal plane than the remaining molars (roots are more developed). MN Specimen 5769 also presents one extra molar on each side, behind the Upper left and right M4. On the right side (Fig. 7), the extra molar is partially erupted. It is dislo- cated, due to the lack of Space on the den- Pr End Hyld Fig.5. RightinferiormolarseriesofDidelphisalbiven- Fig.6. Leftsuperior molarseries ofPhilanderfrenata tris (MN 22250), with a supernumerary molar (arrow). (MC 267), with a supernumerary molar(arrow). Occlu- Occlusalview. Entoconid (End), hypoconid (Hyd), hy- sal view. Protocone (Pr), paracone (Pa), metacone poconulid (Hyld). (Nie), centrocrista(Cc). Supernumerary moLarsin neotropkalopossums 199 iented, and seems to be pushing forward the row. It is reduced, with distinguishable cusps. Discussion The occurrence of dental abnormalities such as supernumerary teeth is a rare and unpredictable phenomenon that makes the study of its specific developmental causes and processes very unlikely. Although the alternative explanations to the supernumerary teeth phenomenon are not always ex- clusive we provide a critical evaluation of some possible explanations. Altoughrare,thefrequencies ofsupernumer- arymolarsreportedhere forthe Didelphidae fall within the ränge of those found in other mammal (placental) groups where the phenomenon has been reported (e.g. 1.6% (9/ 550) in European lynxes (Lynx lynx (Lin- Me naeus, 1758)) Kvam 1985; 0.2% (1/580) in red deers. (Cervus elaphus Linnaeus, 1758) Fig. 7. RightsuperiormolarseriesofPhilanderfrenata and0.8% (1/130) inwapitis (Cervuscanaden- (MN 5769), with a supernumerary molar (arrow). Oc- sis Linnaeus, 1758) Pekelharing 1968; 3.7% clusal view. Protocone (Pr), paracone (Pa), metacone (4/109) in mooses {Alces alces (Linnaeus, (Me), centrocrista (Cc), paracrista (Pc). 1758)), Steele and Parama 1979. tary behind the M4, with its occluAsal plane Fsiurpsetrnitumiesriamrpyortteaetnht atroe caornestiudrenr tiof athleosset of the tooth posteriorly directed. centro- primitive condition, thus being an atavistic crista is also recognisable, as well as proto- character. For instance, Takahashi (1974) cone,paracone andmetacone. The paracris- suggested that the presence of supernumer- ta is also present, and the tooth lacks stylar aryincisors is an atavistic character ofsome cusps C, D and E. On the left side. the extra Didelphis specimens. However, Berkovttz toothismore oddlyformed,with acrown of (1978) states that no more than five incisor ovoid shape. Cusps are perceptible, such as tooth germs were ever observed in Didel- an inner crista, probably the centrocrista. phis. Thus, the supernumerary incisors stu- The occlusal plane, however, is aligned with died by Takahashi (1974) doubtfully can the remaining molars ofthe series. be interpreted as atavistic characters. Furthermore, an atavistic explanation presents some limitations in our case, as the P. opossum basic marsupial dental formula, exhibited One specimen (AMNH 34373) presented a by extant Didelphidae (iJCiPiMj) differs Single supernumerary tooth at the end of from the basic therian formula at the time each superior row. The extra tooth at the of metatherian divergence from eutheria left side is reduced, but otherwise much si- by the lost ofpremolar teeth on the former milar to a normal M4 in cusp patterns. It is (Barbour 1977). Besides the proposition of also at the same occlusal plane of the re- some authors that the third deciduous pre- maining teeth. The extra tooth at the right molars (dP3) could in fact be first molars superior side is occluding anteriorly or- and the subsequent molars being M2 to 200 D. ASTÜADEMoraes etal. M5 (e.g. Hershkovitz 1992), there is no tion of the underlying phenomenon hard. mention of a truly additional fifth molar in Nevertheless, some sort ofrandom develop- marsupials (living or fossil). The only mental disorder could be an explanation for known exception would be the Australian manyofthe caseswestudiedhere. numbatMyrmecobiusfasciatusWaterhouse, Such an explanation is more difficult to ac- MN 1836 (Myrmecobiidae), which can present 5 cept in extreme cases such as 22250 AMNH or 6 molars (Thenius 1989). In this case and 209179, where four almost however, it is believed that the molar num- fully developed molars are present, requir- ber is a secondary specialisation resulting ing a simultaneous event of germ duplica- fromjaw elongation and not related to any tion in all M4. A genetically based distur- ancestral condition, or primitive trait. bance with simple mendelian inheritance is Hence, an atavistic explanation could be also unlikely, as one of the specimens stu- advanced for a possible supernumerary pre- died (MC 267) was field caught but main- molar but not for molars. In fact there is no tained alive for captive breeding, and none fossil record relating the occurrence of five of the offspring prersented any similar phe- molars in marsupials. nomenon. Another hypothesis relates an excessive An alternative explanation could be that size development to the emergence of an the premolariform P3 had erupted without extra tooth at the end of the tooth row. loss of the molariform dP3. If this is the However, as all specimens studied here pre- case, the cheekteeth observedwouldin fact sented Standard sizes for their species, such be, in order: PI, P2, P3, dP3, Ml, M2, M3 a hypothesis does not seem to be the case. and M4. The eruption of the P3 would dis- Furthermore, as we reported, in many cases place the whole molar series (at the time there is actually a lack of Space for these of eruption of the P3, only Ml and M2 are teeth to develop, which however did not present), thus forcing the M3 and M4 to prevent the teeth from appearing and the the end of the maxillar bone, which in case amount of Space available does not seem oflack of Space could explain the deforma- to be related to the completeness of the tions eventually observed. According to tooth formation. Berkovitz (1978), in Didelphis virginiana In some reports the occurrence of supernu- the third premolar develops in the embryo- merary teeth had been related to develop- nic dental lamina between the second pre- mental disorders, such as Splitting of the molar and the deciduous molar. Thus, if tooth germ (Krutzch 1953; Long andLong the deciduous molar was displaced poster- 1965; Pekelharing 1968; Steele and Para- iorly instead of falling, the sequence of the ma 1979). These developmental alterations teeth after eruption would be the one pre- on the embryonic germwill likelylead to an viously stated. However, both Upper and incomplete development ofone or both du- lower deciduous premolars are morphologi- plicated teeth, as observed in cervids, and in cally different from first permanent molars; M some cases resulting in an extra tooth "mir- dP3's are narrower than :,s, and dP3's rored"inrelationtotheoriginalone (Pekel- have narrower trigonids than Mi's, and haring 1968). The supernumerary molars their talonids are bigger in relation to the here reported vary from morphological per- trigonid than in the Mi. In all animals ex- fect M4-like teeth to very small vestigial amined here the first molar in the series teeth, andneverinthis"mirrored" Situation. has all characteristics of an actual Ml, and In fact, no clear association between lack of not of a dP3, which denies this hypothesis. Space and amount of development of the The different shape variations observed in supernumerary tooth could be found. these teeth can be explained by the classic Furthermore, knowledge on precise tooth field model of mammalian heterodonty. development for most of these species is This model postulates that heterodonty de- not existant, and all individuals examined rived by the existence of three morphoge- arefieldcaught,makinganexactdetermina- netic fields (incisor, canine, and molar).