Dental Anomaly in the Early Eocene Condylarth Ectocion Author(s): Kenneth D. Rose and B. Holly Smith Source: Journal of Paleontology, Vol. 53, No. 3 (May, 1979), pp. 756-760 Published by: SEPM Society for Sedimentary Geology Stable URL: http://www.jstor.org/stable/1304020 . Accessed: 11/10/2013 10:52

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This content downloaded from 141.213.236.110 on Fri, 11 Oct 2013 10:52:34 AM All use subject to JSTOR Terms and Conditions 756 PALEONTOLOGICALNOTES ment for this specimen. I am indebted to Dr. Rodendorf, B. B. 1962. Fundamentals of Paleon- Frank Carpenter of Harvard University for tology-reference book for Paleontologists and his and comments in the taxonomic Geologists: Arthropods, Tracheates, and Chelic- help place- Acad. Sci. U.S.S.R. 122-123 ment of this fossil. erates. Moscow, (in Russian). A. G. 1960. On the of the REFERENCES Sharow, system orthop- terous insects. Verhandl. XIth Internat. Kongr. Handlirsch,A. 1911. New Paleozoicinsects from Entomol. Wien 1:295-296. the vicinity of Mazon Creek, Illinois. Amer. J. . 1961. Order Plecoptera: Palaeozoic insects Sci. 31:297-377. of the Kuznetsk Basin (Russ.). Tr. Inst. Palaeon- Martynov,A. V. 1930. Palaeozoicinsects from the tol. Akad. Sci. 85:225-34. KuznetskBasin. Bull. Geog. Prosp. Serv. Mos- cow 49(10):73-111. MANUSCRIPTRECEIVED JANUARY 3, 1978 Richardson,E. S., Jr. 1956. PennsylvanianIn- REVISED MANUSCRIPT RECEIVED SEPTEMBER 16, vertebratesof the Mazon Creek Area, Illinois. 1978 Fieldiana: Geology 12(1-4):28 & 33.

DENTAL ANOMALY IN THE EARLY EOCENE CONDYLARTH ECTOCION

KENNETH D. ROSE AND B. HOLLY SMITH Museum of Paleontology and Department of Anthropology, University of Michigan, Ann Arbor 48109

Dental anomalies are not common in the Since 1975, thousands of specimens of late mammalian fossil record, and few cases have Paleocene and early Eocene mammals have been reported in the paleontological literature. been recovered by University of Michigan The most frequently observed abnormalities Museum of Paleontology (UM) expeditions to include supernumerary teeth, usually at the the Clark's Fork Basin, northern Bighorn Ba- back of the molar series or in the premolar sin, Wyoming. These include more than 500 series, and hypodontia or absence of teeth jaws and hundreds of isolated teeth of the (Wilson, 1955; McKenna, 1960; Archer, 1975; phenacodontid condylarth Ectocion. In 1977, Wang and Wu, 1976; Mellett, 1977). Such the junior author collected an unusual speci- oddities are better known in Recent mammals men of Ectocion osbornianus, UM 69450, at (e.g., Archer, 1975, and references cited there- UM Locality SC-207 (Willwood Formation, in), particularly humans, for which there ex- early Eocene, lower "Gray Bull beds" of early ists an extensive literature in the annals of hu- Wasatchian age). This is the only mammalian man dental pathology. We record here a very fossil in the entire collection that preserves a curious dental anomaly of a type, to our striking anomaly. UM 69450 consists of partial knowledge, not previously mentioned in pa- right and left lower dentitions including right leontological reports. P34 and Ml-3 and left P34 and M3. Both right

TEXT-FIG. 1-Lower teeth of Ectocion osbornianus. A, buccal and B, lingual views of the left anomalous P3, UM 69450. C, lingual D, crown and E, buccal views of the right anomalous P3-4 and normal M,, UM 69450. F, buccal view of normal right P34-MI, UM 65382. Spacing and orientation of teeth in C- E, including relatively low P3 and elevated P4, are due to postmortem distortion. Crown of right P3 (C) is divided almost to base; enamel was originally continuous around the base but appears discontinuous due to breakage. JOURNALOF PALEONTOLOGY,V. 53, NO. 3, MAY 1979 0022-3360/79/0053-0756$01.00 Copyright, ? 1979, The Society of Economic Paleontologists and Mineralogists

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A B

5 mm

D

E

F

This content downloaded from 141.213.236.110 on Fri, 11 Oct 2013 10:52:34 AM All use subject to JSTOR Terms and Conditions 758 PALEONTOLOGICALNOTES and left P3 are severely malformed. The fourth the premolars. The fourth premolar is only premolars also are atypical, though not nearly slightly worn, and P3 displays almost no wear to the degree as the third premolars. The mo- at all. Finally, radiographs of the specimen did lars are structurally normal. not reveal any teeth within the mandible (but The lower P4 in normal Ectocion (Text-fig. see discussion below). Thus the premolars in 1F) is rather variable in morphology. Typi- UM 69450 can be confidently identified as per- cally it is submolariform, differing from the manent teeth. molars in being narrower and having a more In the human dentition, dental abnormali- anteroposteriorly extended trigonid and nar- ties generally have been classified on the basis rower talonid. It has a low paraconid shelf of their morphology. This classification im- directed more anteriorly than in the molars, plies, but is not always consistent with their and the paraconid is weak or absent. The tal- developmental history. Not all anomalies fit onid is basined, with the entoconid usually into the discrete categories, however, and it is well developed (West, 1976) and a distinct hy- the developmental cause of the anomaly that poconulid sometimes present. In UM 69450 should be the subject of investigation. Dou- (Text-fig. 1C-E), P4 has a long trigonid with bled or connate teeth, as in the specimen of a very prominent paraconid. The hypoconid Ectocion described here, have been termed is high, but the postcristid slopes lingually either geminated, twinned, or fused. Gemi- with no indication of either entoconid or hy- nation, resulting in a single tooth that usually poconulid; hence the talonid is not basined. has a bifid crown, is believed to arise from The lower P3 in typical Ectocion is a simple partial division of one tooth bud (Tannen- tooth with a high protoconid, very small para- baum and Alling, 1963; Levitas, 1965; Pind- conid and metaconid variably present, and a borg, 1970). The pulp cavity is that of a single single low talonid cusp (Text-fig. 1F). The tooth. If the geminated tooth is counted as third premolars in UM 69450 (Text-fig. 1A-E) one, the total number of teeth in the affected are elongate, multicusped anomalies. Al- area is normal. Twinning, or schizodontia, is though the left and right P3s are similarly de- the presence of two teeth, usually mirror im- formed, they are not exact mirror images. The ages of each other, interpreted to result from cusp homologies are unclear, for at least two complete cleavage of a single tooth bud (Lev- cusps resemble a protoconid, and each of these itas, 1965). Such a twinned P2 has been ob- appears to be twinned. The left P3 has four served in a late Pliocene canid (Fine, 1964). roots and the right P3 at least three and pos- Fusion, or synodontia, applies to teeth joined sibly four; the precise number is difficult to at the crowns or the roots, or both; the dentine ascertain because of postmortem fracturing of and enamel of both teeth are almost always the mandible. Due to this breakage and to its joined. It is usually said to be a result of union density, radiographs of the fossil also failed to of two or more tooth buds during develop- clarify the root configuration of the right P3. ment, perhaps arising from crowding of tooth To some extent the premolars resemble de- primordia (e.g., Pindborg, 1970). According to ciduous teeth of Ectocion, but several features this interpretation, complete union of the confirm that they are deformed permanent crown and roots, or of only the crowns, will teeth. They are neither lighter in color nor result if fusion occurs early in development of lower crowned than the molars, as is often the tooth germs. If it takes place later in de- distinctive of deciduous teeth (Simpson, 1951; velopment (i.e., after crown formation), the West, 1971). They are broader than typical roots alone will be fused (Bier, 1958). How- milk teeth, and the jaw is deeper and more ever, carpal "fusions" actually result from fail- robust than in juveniles. Deciduous P4 in nor- ure of cartilaginous precursors to separate mal Ectocion is often heavily worn; it is the (Garn et al., 1976), and it has been suggested last deciduous premolar to be replaced and that "fusion" of teeth also ensues from incom- probably the first to erupt (West, 1971). Con- plete division of the dental lamina into sepa- sequently, it should be more heavily worn than rate tooth germs (Hitchin and Morris, 1966). M,. But UM 69450 exhibits the reverse situ- Fusion may be unilateral or bilateral. In ation: M, is conspicuously more heavily worn humans, it is most frequent in the deciduous than the premolars, and even M3 (which is incisors (Clayton, 1956; Bier, 1958), but it has fully erupted) shows at least as much wear as also been observed in deciduous lower pre-

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10mm TEXT-FIG.2-Radiograph of right mandibleof juvenile Ectocion osbornianus,UM 65558, with dP2- dP4, M,i2. Anteriorborder of M3 alveolus indicatesthat Ms was at least partiallyerupted. Roots of deciduouspremolars have not been resorbedand there is no indicationof permanentpremolar calci- fication within the jaw. molars (Grahnen and Granath, 1961), super- development of the premolar anlagen. None- numerary premolars (Shapira, 1974), and in theless, the crown is larger and more complex permanent incisors and second and third mo- than would be expected from this event alone. lars (Tannenbaum and Alling, 1963). Archer The apparent twinning of some of the cusps (1975), in a thorough study of dental abnor- suggests that gemination may also be in- malities in marsupials, observed fusion only in volved, i.e., that the developing tooth buds the premolar series. If the fused teeth are underwent partial division. The ultimate counted as one, the number of teeth in the cause of such abnormalities is not known, but affected area is always less than normal. many factors have been proposed, for example The term "fusion," deriving from the ulti- disease, trauma, and crowding. Many dental mate morphology of the tooth but not neces- anomalies are probably not genetically con- sarily indicative of its early development, may trolled, but there is some evidence that bilat- therefore be a misnomer. Hitchin and Morris eral anomalies may be related to dental mor- (1966) advocate the term connation, which phogenetic fields (Archer, 1975). makes no implication about developmental During the course of this study, we exam- history. ined a number of juvenile specimens of Ecto- The complex crown of P3 in UM 69450 is cion preserving deciduous teeth. Radiographs completely united (Text-fig. 1A-E), but ap- of some of them indicate that permanent pre- pears to incorporate at least two teeth. This molars in Ectocion may calcify at a relatively inference may also be drawn from the presence later stage than in many other mammals. For of more than two roots. These features suggest example, even in some individuals of Ectocion that the anomaly arose through fusion (or in- in which M3 is partially erupted, the deciduous complete separation) of two tooth germs- premolars are still functional and there is little either those of P2 and P3, or perhaps of P3 and or no evidence of permanent tooth formation a supernumerary premolar-probably early in within the jaw (Text-fig. 2; see also West,

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1971: fig. 2). A similar situation can be found and A. B. Lewis. 1963. Phylogenetic and in- in the Oligocene insectivore Leptictis acuti- tra-specific variations in tooth sequence poly- In D. R. An- dens (West, 1972), in which molars erupted morphism. Brothwell (ed.), Dental before wear occurred on deciduous thropology, p. 53-73. Pergamon Press, New significant York. In some near- premolars. mammals, however, -- , -- and D. W. Shoemaker. 1956. The se- ly fully formed permanent premolars lie within quence of calcification of the mandibular molar the jaw while deciduous premolars are still and premolar teeth. J. Dent. Res. 35(4):555-561. functional and some molars have not yet Grahnen, H. and L. Granath. 1961. Numerical erupted (see, e.g., Garn and Lewis, 1963: fig. variations in primary dentition and their corre- lation with the dentition. 1; 1973: 1977: permanent Odont. Rose, fig. 5; Mellett, fig. 52). 12:348-357. of calcification and Revy Sequences eruption vary Hitchin, A. D. and I. Morris. 1966. Geminated both between and intra- considerably species odontome-connation of the incisors in the dog- specifically, and the sequence of development its etiology and ontogeny. J. Dent. Res. Supple- is not always the same as that of eruption ment to no. 3, 45:575-583. (Garn et al., 1956; Slaughter et al., 1974; Levitas, T. C. 1965. Gemination, fusion, twin- and concrescence. Dent. Children 32:93- Schwartz, 1975). Hence it is not ning, J. surprising 100. that UM 69450 and other individuals of com- McKenna, M. C. 1960. The Geolabidinae, a new have functional parable age permanent pre- subfamily of early Cenozoic erinaceoid insecti- molars, whereas in apparently only slightly vores. Univ. Calif. Publ. Geol. Sci. 37(2):131- younger individuals the permanent premolars 164. have hardly begun to calcify. Mellett, J. S. 1977. Paleobiology of North Amer- ican Hyaenodon (Mammalia, Creodonta). Con- trib. Vert. Evol. 1:1-134. ACKNOWLEDGMENTS Pindborg, J. J. 1970. Pathology of the dental hard We are indebted to Dr. P. D. Gingerich tissues. W. B. Saunders, Philadelphia, 443 p. (UM) for permission to describe this unusual Rose, K. D. 1973. The mandibular dentition of Bre- specimen. Professors S. M. Garn and A. R. Plagiomene (Dermoptera, Plagiomenidae). viora 411:1-17. Burdi of the Center for Human Growth and Schwartz, H. 1975. Re-evaluation of the mor- of J. Development, University Michigan, helped phocline of molar appearance in the Primates. Fo- to clarify several points regarding dental de- lia Primatol. 23:290-307. velopment. Drs. Garn and Gingerich and Mr. Shapira, Y. 1974. Fused supernumerary mandib- D. W. Krause provided helpful criticisms of ular premolar. J. Dentistry 2(5):209-210. the manuscript. Text-figure 1 was skillfully Simpson, G. G. 1951. American Cretaceous insec- drawn Ms. Karen and the radio- tivores. Amer. Mus. Novitates 1541:1-19. by Payne, B. R. H. Pine and N. E. Pine. were Slaughter, H., graphs, including Text-figure 2, pre- 1974. Eruption of cheek teeth in Insectivora and pared by Professor A. G. Richards of the Uni- Carnivora. J. Mammal. 55(1):115-125. versity of Michigan School of Dentistry. Ms. Tannenbaum, K. A. and E. E. Alling. 1963. Karna Steelquist assisted with photography. Anomalous tooth development. Case reports of To all of them we extend our appreciation. gemination and twinning. Oral Surg. 16(7):883- This research was in NSF 887. supported part by and Wu Maolin. 1976. A dental Grant DEB 77-13465 to Dr. P. D. Wang, Linghong Gingerich. anomaly of Ailuropoda melanoleuca baconi. Vert. Palas. 14(4):263-266. REFERENCES West, R. M. 1971. Deciduous dentition of the early Archer, M. 1975. Abnormal dental development Tertiary Phenacodontidae (Condylarthra, Mam- and its significance in dasyurids and other mar- malia). Amer. Mus. Novitates 2461:1-37. supials. Mem. Queensland Mus. 17(2):251-265. .1972. Upper deciduous dentition of the Oli- Bier, S. J. 1958. Fusion. N.Y. State Dent. J. gocene insectivore Leptictis (=Ictops) acutidens. 24:246-247. Ann. Carn. Mus. 44(3):25-32. Clayton, J. M. 1956. Congenital dental anomalies .1976. The North American Phenacodonti- Biol. occurring in 3557 children. J. Dent. Children dae (Mammalia, Condylarthra). Contrib. 23:206-208. and Geol. Milwaukee Public Mus. 6:1-78. Fine, M. D. 1964. An abnormal P2 in Canis cf. C. Wilson, R. W. 1955. Two cases of dental anomaly latrans from the Hagerman Fauna of Idaho. J. in early Tertiary mammals. Trans. Kansas Acad. Mammal. 45(3):483-485. Sci. 58(4):514-518. Garn, S. M., A. R. Burdi and W. J. Babler. MANUSCRIPT RECEIVED MAY 19, 1978 1976. Prenatal origins of carpal fusions. Am. J. REVISED MANUSCRIPT RECEIVED SEPTEMBER 12, Phys. Anthrop. 45(2):203-208. 1978

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