THE SPECIALIZED STRUCTURE of HYAENID ENAMEL: DESCRIPTION and DEVELPOMENT WITHIN the LINEAGE - INCLUDING PERCROCUTIDS Clara Stefen1* and John M
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Scanning Microscopy Vol. 13, No. 2-3, 1999 (Pages 363-380) 0891-7035/99$5.00+.25 Scanning Microscopy International, Chicago (AMFStructure O’Hare), of IL hyaenid 60666 USAenamel THE SPECIALIZED STRUCTURE OF HYAENID ENAMEL: DESCRIPTION AND DEVELPOMENT WITHIN THE LINEAGE - INCLUDING PERCROCUTIDS Clara Stefen1* and John M. Rensberger2 1Staatliches Museum für Naturkunde, Museum am Löwentor, Stuttgart, Germany, 2Department of Geological Sciences and Burke Museum, University of Washington, Seattle, Washington, USA (Received for publication November 14, 1996 and in revised form June 13, 1997) Abstract Introduction The tooth enamel of hyaenas has a highly special- Phylogenetic and taxonomic associations of certain ized structure adapted to their diet. Hyaenid enamel is enamel structures have been recognized for many years characterized by a type of Hunter-Schreger-Bands (HSB) (e.g. Korvenkontio, 1934; Kawai, 1955; Boyde, 1965; Martin, with a complex 3-dimensional structure showing a zigzag 1992). But recently it has become clearer that some enamel pattern when viewed tangentially. This structure, also found microstructural morphologies also have functional roles in in other carnivorous mammals of different phyletic affini- the chewing mechanism (Von Koenigswald, 1980; ties in which it must have evolved independently, is Rensberger and Von Koenigswald, 1980; Pfretzschner, 1986, described and its distribution among hyaenid taxa is 1994; Young et al., 1987; Von Koenigswald and Pfretzschner, documented. Hyaenids also have another specialization: in 1991; Rensberger and Pfretzschner, 1992; Marx, 1994), which the shearing blade of the carnassials the HSB turn upwards makes the selective factors involved in the origins of enamel more strongly than in other carnivorans to intersect the microstructures more readily determinable and provides cutting edge at roughly a right angle. This bending of the additional information about the feeding behaviours of HSB occurs on the buccal side of the paracone and extinct taxa. posteriorly through the metastyle in the upper P4 and at the Differences in enamel microstructure are known to lingual side of the protoconid and the paraconid of the lower correlate with factors involved in the processing of food. M1. The zigzag pattern may be derived from undulating Microwearstudies demonstrate correlations between the HSB, judging from the taxo-nomic distribution of these struc- striae and pit characteristics and food type (O‘Leary and tures and the phyletic relationships of the taxa. The Teaford, 1992; Hojo, 1996). Enamel surfaces are anisotropic extensiveness of zigzag HSB increased within the dentition in their rates of wear, which depend on the direction of during the evolution of hyaenids. The occurrence of the prisms (Rensberger and Von Koenigswald, 1980; Boyde and zigzag pattern in as-sociation with bone-eating habits in Fortelius, 1986; Young, McGowan, and Daley, 1987). Prism living taxa suggests that this structure strengthens the decussation is better developed in mammals with strong enamel to resist the high stresses accompanying the chewing musculature and high occlusal stresses (Von fracturing of hard, tough objects such as bones. The Koenigswald et al., 1987); it is weakly developed in primates restriction of upturned HSB to the carnassial blades in the that eat soft foods but more pronounced in species that dentitions of hyaenids and the upturning of less specialized include hard foods in their diets (Maas, 1986). Prism HSB in the same region in other carnivorous taxa suggests decussation is organized differently in teeth with ellipsoi- that this structure maintains the sharp edge required for dal cusps compared with teeth in which lophs are developed this function. (Pfretzschner, 1986; Rensberger and Von Koenigswald, 1980; Fortelius, 1985). These differences have been shown to be Key Words: Enamel microstructure, Hunter-Schreger-Bands, related to the differences in directions of chewing-induced zigzag HSB, prism decussation, ossiphagy, bone-crushing, stresses in the enamel (Pfretzschner, 1986; Rensberger and Hyaenidae, Percrocutidae, Mammalia Pfretzschner, 1992, Rensberger, 1993). Most of the data in the above studies are based on *Address for correspondence the enamel of herbivorous mammals. Carnivore enamel has Clara Stefen been rarely studied except for an early preliminary description Staatliches Museum für Naturkunde, Museum am Löwentor, of carnivores of different systematic affinities by Tomes Rosenstein 1, 70191 Stuttgart, Germany (1906) and descriptions of some single species (e.g. Reif, Telephone Number: 49 711 8936 172 1974: Canis familiaris and Cynodictis; Skobe et al. 1985: FAX Number: 49 711 8936 100 Canis familiaris and Felis domestica; Von Koenigswald, e-mail: [email protected] 1992: Ursus spelaeus). An overview of carnivore enamel is 363 C. Stefen and J.M. Rensberger given by Stefen (1997). References to the specialized hyaenid Bonn enamel have been made several times in recent literature KOE Enamel sample collection of Prof. W. von (Von Koenigswald, 1992; Rensberger, 1993, 1995) and it may Koenigswald, Inst. für Paläontologie, Bonn have been observed by other workers too. Rensberger (1995), using a 3-dimensional finite element model of the Materials canine, showed that the most highly folded HSB of the canine in Crocuta crocuta are developed only in the region The 3-dimensional structure of hyaenid HSB is based where the highest tensile stresses are likely to occur. on teeth of Crocuta crocuta that were obtained from several The structure of hyaena enamel has not been sources. For light microscopic studies, we examined full described for the other teeth of the dentition, including the dentitions in Recent specimens from ZFMK, FMNH, a partial posterior premolars where the primary bone-crushing occurs dentition from the Zooarchaeology collections of the in hyaenas. In the present paper we present a detailed Transvaal Museum, South Africa, isolated teeth from GPIBO interpretation of the structure for the entire dentition in (Pleistocene cave specimens) and specimens provided by Crocuta crocuta and describe how these structures are several individuals (see Acknowledgements). For scanning distributed in the other members of the Hyaenidae. electron microscopy, we examined KOE specimens 1234 and The specialized structure, here termed zigzag HSB 1183; specimen A3650 from the Zooarchaeology collections (Hunter-Schreger-Bands, layers of decussating prisms) has of the Transvaal Museum, South Africa. first been thought to be characteristic for the Hyaenidae, but this is not the case as has been shown by Stefen, 1995, Methods 1997). Zigzag HSB occur in different families of Carnivora (Mustelidae, Amphicyonidae, Ursidae, Canidae, Felidae, Where HSB are close to the surface they can be Hyaenidae and Otariidae), Condylarthra (Mesonychidae) observed by light-optical methods without preparation of and Artiodactyla (Entelodontidae). the teeth (Von Koenigswald, 1980). Most specimens in Our discussion of the Hunter-Schreger-Bands here curated museum collections were studied in this way. emphasizes their three dimensional configuration and how Examining sections made in different planes is important for the structure varies through the thickness of the enamel understanding the 3-dimensional arrangement of prisms. and in different regions of the posterior teeth. We also When material for sectioning was available, teeth were discuss the phylogenetic implications of the distribution of embedded in polyester resin or epoxy resin and sectioned these structures in the Hyaenidae. In a paper in preparation, in horizontal, vertical and tangential planes. Tangential we will analyze the functional implications of the various sections were made by grinding either from the outer surface enamel microstructural specializations of hyaenas. or from the dentinal surface in order to reveal the structure Some parameters, for example prism shape and the at varying distances from the enamel-dentine junction (EDJ). thickness of the Hunter-Schreger-Bands, could only be Ground sections were etched with 2N HCl, cleaned in an determined for Crocuta and Proteles because material from ultrasonic bath, dried and sputtered with gold or gold- other taxa was not available for sectioning. However, the palladium for 3 to 12 minutes, sometimes in separate coating HSB of several other fossil and recent hyaenid taxa are episodes in which the specimen was rotated. These sections described on the basis of light microscopic methods and were examined by both light and scanning electron interpreted with regard to phylogenetic and taxonomic microscopy. associations. In the descriptions, the terms undulating HSB, acute- angled HSB, and zigzag HSB are used, which are briefly Abbreviations explained in Fig. 1 (for further details see Stefen 1997). If several types of HSB are present in one tooth, AMNH American Museum of Natural History, New York undulating bands usually occur at the enamel base and BSP Bayerische Staatssammlung für Paläontologie, more acute-angled HSB in the middle region and zigzag HSB München near the tip. Because the transition from undulating HSB to F:AM Frick American Mammals Collection, AMNH, New zigzag HSB always involves a few acute-angled bands, this York is not repeated in each description. FMNH Field Museum of Natural History Zoology Collection, Chicago Results GPIBO Geologisch und Paläontologigsches Insititut der Universität, Bonn In the enamel of Crocuta crocuta, a conspicuous SMNS Staatliches Museum für