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The dentition of Carodnia vieirai (Mammalia: Xenungulata): enamel microstructure and mastication pattern

Lílian Paglarelli Bergqvist and Wighart von Koenigswald

Plain Language Abstract

Carodnia is one of the largest mammals from the Paleogene of South America. It has no extant relatives but its general morphology resembles that of a tapir. Its phylogenetic relationship to other mammals is still under discussion. The tooth enamel microstructure provides, in some cases, information about the systematic position. The pattern of mastication is important for understanding the feeding of an animal. Therefore, these two aspects were investigated to enlarge the base for comparisons with other mammalian dentitions. The specific tooth enamel microstructure of Carodnia is unique, and therefore it does not provide a conclusive key for its systematic position. The pattern of mastication indicates a folivorous diet. A similar pattern of mastication evolved convergently in various mammalian lineages during the early Paleogene, but is almost absent in the dentitions of extant mammals.

RESUMO

Dentes pós-caninos de Carodnia vieirai, do Paleógeno do Brasil, foram investigados quanto à microestrutura do esmalte e o padrão de mastigação. O esmalte é inteiramente prismático e a matriz interprismática (IPM) está orientado paralelamente aos prismas, que consistem dos padrões 1 e 2 de Boyde. As proeminentes bandas de Hunter-Schreger (HSB) verticais estão restritas a uma zona mais externa, enquanto que a zona interna é formada por HSB transversal, mas irregular. Essa é uma combinação muito rara em dentes de mamíferos, mas mostra algumas semelhanças com o schmelzmuster de alguns perissodáctilos específicos, onde evoluiu de forma independente. Diferenças significativas de Astrapotheria foram encontradas. O padrão de mastigação pode ser definido a partir da orientação das facetas de desgaste nos lofos transversais. Em dentes com estágios de desgaste moderado, os lofos possuem facetas planas em apenas um dos lados do dente, as quais estão inclinadas de forma antagônica nos dentes superiores e inferiores. As cristas de esmalte dos "leading sides" cortam como tesouras. Em seguida, as cristas deslizam umas sobre as outras e comprimem os alimentos até a oclusão central. Assim, o movimento da mandíbula durante a fase I é predominantemente mesial com uma distinta inclinação para cima. Não há indícios da existência da fase II na mastigação. Nem o esmalte nem o padrão de mastigação amplamente distribuído oferecem argumentos convincentes para apoiar qualquer uma das propostas filogenética envolvendo Carodnia vieirai. O raro schmelzmuster contribui para a diversidade de microestruturas de esmalte em ungulados sul-americanos.

Palavras-chave: Xenungulata, Bacia de Itaboraí, schmelzmuster, mastigação, bandas de Hunter-Schreger (HSB), método de luz refletida (RLM).

Translation: Author

Resumen en Español

La dentición de Carodnia vieirae (Mammalia: Xenungulata): microestructura del esmalte y patrón de masticación

Se investigaron los dientes caninos posteriores de Carodnia del Paleogeno de Brasil con respecto a la microestructura del esmalte y el patrón de masticación. El esmalte es enteramente prismático y la matriz interprismática (IPM) está orientada paralelamente a los prismas, los cuales se corresponden con los patrones 1 y 2 de Boyde. Las prominentes bandas verticales Hunter-Schreger (HSB) están restringidas a una zona externa, mientras que la zona interna está formada por HSB transversales pero irregulares. Tal combinación es muy rara en dientes de mamíferos, pero muestra algunas similitudes con schmelzmuster de perisodáctilos específicos, donde evolucionó independientemente. Se encontraron diferencias significativas con Astrapotheria. El patrón de masticación puede derivarse de la orientación de las facetas de desgaste en las crestas (lophs) transversales. En etapas de desgaste moderado de los dientes, las crestas tienen facetas planas unilaterales que están inclinadas en los dientes superior e inferior de forma antagónica. Las crestas del esmalte en los lados principales cortan como tijeras. Posteriormente, las crestas antagónicas de corte de las otras crestas o lophs se pasan entre sí y comprimen los alimentos hasta la oclusión central. Así, el movimiento de la mandíbula durante la fase I es predominantemente mesial con una inclinación distinta hacia arriba. Ninguna pista indica una fase II de la carrera de potencia. Ni el esmalte ni el patrón de masticación ampliamente distribuido ofrecen argumentos convincentes para apoyar cualquiera de las relaciones filogenéticas de Carodnia propuestas. El raro schmelzmuster contribuye a la diversidad de las microestructuras del esmalte en los ungulados suramericanos.

Palabras clave: Xenungulata; Cuenca de Itaboraí; Schmelzmuster; masticación; bandas verticales Hunter-Schreger (HSB); método de luz reflectante (RLM)

Traducción: Enrique Peñalver (Sociedad Española de Paleontología)

Résumé en Français

text

Translator: Antoine Souron

Deutsche Zusammenfassung

DIE BEZAHNUNG VON CARODNIA VIEIRAI (MAMMALIA, XENUNGULATA)- SCHMELZMUSTER UND KAUWEISE

Die Backenzähne von Carodnia aus dem Paleogen von Brasilien wurden im Hinblick auf den Zahnschmelz und die Kaubewegung untersucht. Der Schmelz ist durchgehend prismatisch, und die IPM ist parallel zu den Prismen. Die auffallenden, vertikal ausgerichteten Hunter-Schreger-Bänder (HSB), die bereits früher beschrieben wurden, sind auf die äußere Zone des Schmelzmusters begrenzt. Die innere Zone wird von irregulären, transversal ausgerichteten HSB gebildet. Diese Kombination tritt nur sehr selten im Säugetierschmelz auf. Eine gewisse Übereinstimmung wurde bei einigen Perissodactyla gefunden. Dort ist sie aber sicherlich unabhängig entstanden. Deutliche Unterschiede wurden gegenüber den Astrapotheria gefunden.

Die Kaubewegung kann von den Facetten auf den quergestellten Lophen abgeleitet werden. Bei einem mäßigen Abkauungsgrad zeigen sie stets einseitige planare Facetten, die auf den oberen und unteren Zähnen antagonistisch geneigt sind. Die Schmelzkanten auf der Luvseite schneiden wie eine Schere. Anschließend gleiten die Scherblätter über die planeren Facetten und komprimieren die Nahrung bis zum zentralen Kieferschluss. Demzufolge wird der Unterkiefer während der Phase I im Wesentlichen nach mesial und mit einer starken Inklination nach oben geführt. Im Kauschlag kann keine Phase II nachgewiesen werden.

Weder der Schmelz noch die Kaubewegung bieten überzeugende Argumente für eine phylogenetische Beziehung zu anderen Säugergruppen. Das seltene Schmelzmuster erweitert allerdings die Vielfalt der schmelzstrukturen bei den Huftieren Südamerikas.

Schlüsselwörter: Xentungulata, Itaborai Becken, schmelzstrukturen, Kauweise, vertikale Hunter-Schreger Bänder (HSB), Reflektierende Licht Methode.

Translator: Author

Arabic

Translator: Ashraf M.T. Elewa

 

 

FIGURE 1. Carodnia vieirai. (1.1) Fragmented skull (DGM 335M) and (1.2) right mandibular ramus (DGM 334M); (1.3) life reconstruction and its comparative size to other Itaboraí species (from left to right: Tetragonostylops apthomasi (Astrapotheria), Patene simpsoni (Metatheria), Colbertia magellanica (Notoungulata), Riostegotherium yanei (Xenarthra); art by Rodolfo Nogueira.

figure1

 

FIGURE 2. Carodnia vieirai (UFRJ-DG 315M), vertical (2.1-2) and transverse (2.3) sections of a left p1 in reflected light images (RLM). The grounded, etched and sputter coated sections were illuminated almost tangentially from different sides, indicated by the arrows framing the lamps. Areas of similar prisms orientation reflect in the light in the same intensity. The vertical section (2.1) is passing through the tip, whereas (2.2) shows the labial side, about the midpoint. All sections show the difference between the inner and the outer zone. The location of the light bulb in each photography shows where the illumination come from.

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FIGURE 3. Crystallites and prisms in the enamel of Carodnia vieirai. SEM images. (3.1) Prisms in a tangential section (KOE 4122) with open prism sheaths. The crystallites are not visible. (3.2) Crystallites forming prisms and inter prismatic matrix in a tangential section (KOE 4212a). The rounded prisms have a closed prism sheath. (3.3) Transversal section of UFRJ-DG 315M showing prisms in cross-section with open prism sheaths etched away and appearing as a trench. (3.4) Prisms in HSB show different directions. One set occurs in cross-section the other more tangentially. Detail from the outer layer in a transverse section (KOE 4212e). (3.5) The enamel near the outer enamel surface in a transverse section (KOE 4121d). The prisms continue until the OES. IPM - interprismatic matrix, OES - outer enamel surface,.P - prisms, PS - prism sheath.

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FIGURE 4. Vertical (4.1) and transverse (4.2) sections of the sputtered enamel of Carodnia vieirai in RLM. (4.1) KOE 4121, (4.2) KOE 4133. The arrow indicates the direction toward the occlusal surface.

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FIGURE 5. Transverse section of the enamel in Carodnia. Mosaic of two SEM images of KOE 4121, which shows the innermost zone of radial enamel, the inner zone of transverse HSB and the outer zone of vertical HSB. EDJ - enamel-dentine junction, OES - outer enamel surface.

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FIGURE 6. Vertical Hunter-Schreger bands in tangential sections of the enamel of Carodnia vieirai (KOE 4121). (6.1) and (6.2) show the orientation of the HSB illuminated in RLM. Note in (6.2) the changing direction towards the outer rim at the right. In higher magnification in the SEM image (6.3) the transitional zones appears somewhat darker.

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FIGURE 7. Tooth wear in the bilophodont molars of Carodnia vieirai. (7.1) Initial facets on the distal sides of the anterior loph of the left m2 (paratype, DGM 334M). (7.2) Planar wear facets on m2-m3 in a later stage of wear (holotype, DGM 333M). (7.3) Scheme for three stages of the interaction of lophs during phase I of the power stroke: cutting, compressing, central occlusion (modified from Koenigswald, 2014). (7.4) Mastication compass symbolizing the jaw moment in almost mesial direction with a high inclination.

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bergqvistLílian Paglarelli Bergqvist. Departamento de Geologia, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos 274, Prédio CCMN, 21941-611, Rio de Janeiro/RJ, Brasil. This email address is being protected from spambots. You need JavaScript enabled to view it.

Lilian P. Bergqvist is a paleontologist and associate professor at Universidade Federal do Rio de Janeiro, Brazil. Since 1996 she has been working with Paleogene mammals recovered at Itaboraí basin, Brazil, focusing on teeth and postcranial morphology with systematic and functional purposes. More recently she has been conducting paleohistological, paleopathological and taphonomic studies with her various PhD students on Paleogene and Pleistocene fossils. She is also engaged in public awareness of science.

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koenigWighart von Koenigswald. Universität Bonn, Steinmann-Institut (Paläontologie), Nussallee 8, D-53115 Bonn, Germany. This email address is being protected from spambots. You need JavaScript enabled to view it.

Wighart v. Koenigswald is a paleontologist and professor emeritus at the University of Bonn, Germany. He discovered the complexity of the mammalian enamel differentiating between crystallites, prisms enamel types, and schmelzmuster. He and his various PhD students investigated the enamel in various mammalian groups and tested their systematic significance. Additionally he uses the wear facets to reconstruct the pattern of mastication in mammalian dentitions.