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Dental Anomaly in the Early Eocene Condylarth Ectocion Author(S): Kenneth D

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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 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. SEPM Society for Sedimentary Geology is collaborating with JSTOR to digitize, preserve and extend access to Journal of Paleontology. http://www.jstor.org 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 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 PALEONTOLOGICAL NOTES 757 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- 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 PALEONTOLOGICALNOTES 759 10mm TEXT-FIG.2-Radiograph of right mandibleof juvenile Ectocion osbornianus,UM 65558, with dP2- dP4, M,i2.
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  • (Mammalia, 'Condylarthra'), from the Torrejonian

    (Mammalia, 'Condylarthra'), from the Torrejonian

    SIZE VARIATION IN POPULATIONS OF TETRACLAENODON (MAMMALIA, ‘CONDYLARTHRA’), FROM THE TORREJONIAN NALMA OF THE SAN JUAN BASIN, NEW MEXICO, REVEALS NEW INSIGHTS INTO THEIR EVOLUTION AND PALEOENVIRONMENT HOLPIN, Sofia, University of Edinburgh, Edinburgh, Scotland; WILLIAMSON, Thomas E., New Mexico Museum of Natural History, Albuquerque, NM, United States of America; SHELLEY, Sarah L., Carnegie Museum of Natural History, Pittsburgh, PA, United States of America; BRUSATTE, Stephen, University of Edinburgh, Edinburgh, United Kingdom After the end-Cretaceous mass extinction, approximately 75% of life on land and in the sea disappeared. The mammals of the early Cenozoic rapidly diversified and dispersed, rising to numerical and ecological dominance beyond their Mesozoic norms. Among those initial groups that ushered in the Age of Mammals, Paleocene and Eocene ‘condylarths’ are thought to include the ancestors of modern odd-toed ungulates (horses, tapirs, rhinos). Tetraclaenodon is the oldest genus of the ‘condylarth’ group Phenacodontidae and one of the most abundant fossils from the San Juan Basin (SJB) of New Mexico. Tetraclaenodon was a medium sized (mean body mass ca. 10kg), terrestrial mammal which was lightly built and had an omnivorous to herbivorous bunodont dentition. Here we use multivariate and statistical analyses to investigate body mass and dental variation in 110 teeth of Tetraclaenodon spanning the Torrejonian (Paleocene) interval of the SJB. The specimens were grouped into six time bins by their biostratigraphical reference, from Tj1 (~63.8 Ma) through Tj6 (~62.7 Ma). Measurements of the length, mesial and distal width of the lower first molars (m1) were subject to principal component analysis (PCA), and m1 area was used to predict body mass using a regression equation.
  • Paleocene Emergence of Elephant Relatives and the Rapid Radiation of African Ungulates

    Paleocene Emergence of Elephant Relatives and the Rapid Radiation of African Ungulates

    Paleocene emergence of elephant relatives and the rapid radiation of African ungulates Emmanuel Gheerbrant1 Unite´Mixte de Recherche 7207, Centre National de la Recherche Scientifique, Centre de Recherches sur la Pale´obiodiversite´et les Pale´oenvironnements, Case 38, De´partement Histoire de la Terre, Muse´um National d’Histoire Naturelle, 8, Rue Buffon, 75005 Paris, France Edited by Elwyn L. Simons, Duke University Lemur Center, Durham, NC, and approved May 11, 2009 (received for review January 14, 2009) Elephants are the only living representatives of the Proboscidea, a Systematic Palaeontology formerly diverse mammalian order whose history began with the Placentalia Owen, 1837 55-million years (mys) old Phosphatherium. Reported here is the Paenungulata Simpson, 1945 discovery from the early late Paleocene of Morocco, ca. 60 mys, of Proboscidea Illiger, 1811 the oldest and most primitive elephant relative, Eritherium azzou- Family indet. zorum n.g., n.sp., which is one of the earliest known representa- Eritherium azzouzorum n.g., n.sp. tives of modern placental orders. This well supported stem pro- (Figs. 1 and 2). boscidean is extraordinarily primitive and condylarth-like. It provides the first dental evidence of a resemblance between the Etymology. Eritherium (monotypic genus), from eri (g.), early, proboscideans and African ungulates (paenungulates) on the one and therion (g.), beast; azzouzorum, species dedicated to people hand and the louisinines and early macroscelideans on the other. from Ouled Azzouz village close to Sidi Chennane, who recov- Eritherium illustrates the origin of the elephant order at a previ- ered most of the fossils. ously unknown primitive stage among paenungulates and ‘‘ungu- lates.’’ The primitive morphology of Eritherium suggests a recent Locality and Age.