HUNTER-SCHREGER BAND CONFIGURATION AND MICROWEAR OF OLIGOCENE AGE HYRACODON AND SUB-HYRACODON TOOTH ENAMEL

Teeth of early mammals provide evidence of the environment in which individuals lived as well as their dietary habits. Particularly useful paleoecological indicators include the varying configurations of Hunter-Schreger Bands (HSB), which are prisms in the enamel that strengthen teeth; these features can easily be confused with growth lines (perikymata). Some research suggests that HSB type is determined by taxonomic lineage, although this has not been confirmed. In addition to these structural elements, various microwear features, including scratches and pits formed during life likely indicate abrasion from chewing and provide insights to dietary components.

This study is an examination of teeth samples collected from the Oligocene White River Formation, including teeth of Hyracodon nebraskensis and Caenopus occidentalis. The aim is to provide additional observations to augment or compare to previous research by Koenigswald et al. (2011), who described HSB in the same fauna, and Tseng (2012) who described similar microwear features in carnivores. The objectives being tested are whether: a) there is a relationship between type of HSB and degree of microwear and b) the extent of microwear in herbivores (the two taxa listed above) vs. carnivores (studied by Tseng, 2012). Two types of HSB have been identified previously for these fauna. To date, this study has found examples of one HSB configuration, as well as perikymata, supporting work by Koenigswald et al. (2011). Larger (posterior) teeth tend to show HSB more prominently, due to the thicker enamel present. HSB were observed on occlusal, buccal, and lingual surfaces. Other microwear features observed include pits and scratches indicating abrasion from chewing. Additional examination will include a more detailed analysis of the extent of microwear among the two taxa studied as well as a comparison of microwear extent and type of HSB.

References:

von Koenigswald, W., Holbrook, L.T., and Rose, K.D., 2011, Diversity and evolution of Hunter-Schreger band configuration in tooth enamel of perissodactyl mammals: Acta Palaeontologica Polonica, v. 56, p. 11-32.

Tseng, Z.J., 2012, Connecting Hunter-Schreger band microstructure to enamel microwear features; new insights from durophagous carnivores: Acta Palaeontologica Polonica, v. 57, p. 473-484.