Microwear evidence for Plio–Pleistocene bovid diets from Makapansgat Limeworks Cave, South Africa

Abstract

Makapansgat Limeworks Cave is a well-known Australopithecus africanus bearing locality that has spawned a considerable amount of paleoecological research because of its hominin component. Most recently, the paleoecology of this Plio–Pleistocene site has been studied by determining the diet and habitat of other extinct taxa, particularly the bovids. The diets of seven bovids (Aepyceros sp., Gazella vanhoepeni, Makapania broomi, Parmularius braini, Redunca darti, Tragelaphus sp. aff. T. angasii, and Tragelaphus pricei) have now been classified using taxonomic uniformitarianism, ecomorphology, stable carbon isotopes, and mesowear analysis. Here, dental microwear is applied to the same bovids for additional comparison and to further elucidate the strengths and weaknesses of each method. The different dietary proxy methods noted provide a temporal continuum, with genetic signals such as ecomorphology and taxonomic uniformitarianism indicating behavioral adaptations over geologic time, while nongenetic data such as stable carbon isotopes and mesowear reflect different aspects of average diet over extended portions of an animal's life, and dental microwear provides dietary snapshots.

Microwear separated an extant baseline of ten bovid species into expected dietary categories and the Makapansgat bovids clearly fell into two groups with the same degree of separation as between extant grazers and browsers. The results indicate that a multidisciplinary approach produces a more accurate and robust reconstruction of past diets. In sum, the microwear analysis is in-line with the isotope and mesowear results, which suggest a stronger browsing component than either taxonomic uniformitarianism or ecomorphology imply.

Introduction

Mammalian paleoecology has traditionally focused on taxonomic uniformitarianism. This method is based on the assumption that fossil taxa evince the ecological preferences of their closest living relatives. While this technique is certainly of some value in analyzing relatively recent faunas, its utility in determining the paleoecology of extinct taxa is questionable. The main problems with this method are that it requires taxonomic groups to remain ecologically constant through time and it provides little or no information about extinct forms with no living relatives (Sponheimer et al., 1999).

A number of techniques have been developed in recent years that take a more empirical approach to dietary reconstruction, such as (1) ecomorphology, or morphological studies that reflect long-term ecological adaptations (e.g., Janis, 1988, Janis and Fortelius, 1988, Solounias and Moelleken, 1993a, Solounias and Moelleken, 1993b, Solounias et al., 1995, Spencer, 1995, Reed, 1996), (2) stable carbon isotopes (e.g., Aufderheide, 1989, Lee-Thorp et al., 1989, Sponheimer et al., 1999, Ambrose and Katzenberg, 2000, Lee-Thorp and Sillen, 2001), (3) dental microwear, the study of short-lived microscopic wear patterns on teeth (e.g., Solounias et al., 1988, Teaford, 1988a, Teaford, 1988b, Solounias and Moelleken, 1993b, Solounias and Hayek, 1993, Rose and Ungar, 1998, Solounias and Semprebon, 2002, Rivals and Deniaux, 2003, Merceron et al., 2004a, Merceron et al., 2004b), and (4) dental mesowear, the study of cusp wear patterns over an extended period of an animals lifetime (e.g., Fortelius and Solounias, 2000, Kaiser et al., 2000, Franz-Odendaal, 2002, Kaiser and Solounias, 2003, Kaiser and Fortelius, 2003, Franz-Odendaal and Kaiser, 2003, Franz-Odendaal et al., 2003, Schubert, in press). Researchers have also combined some of these techniques showing that multiple methods result in more solid paleodietary reconstructions (e.g., Solounias and Moelleken, 1993b, MacFadden et al., 1999, Sponheimer et al., 1999).

A great deal of research has focused on reconstructing the environment of Makapansgat. Methods for interpreting the paleoenvironment of the site have ranged from pollen analysis (Cadman and Rayner, 1989, Rayner et al., 1993, Zavada and Cadman, 1993) to taxonomic uniformitarianism (e.g., Wells and Cooke, 1956, Vrba, 1982) and ecomorphology (Reed, 1996, Reed, 1998). More recent work has focused on testing taxonomic uniformitarianism of bovids by comparing these results to ecomorphology and stable carbon isotopes (Sponheimer et al., 1999). This interdisciplinary study led Sponheimer et al. to suggest that two taxa (Aepyceros sp. and Gazella vanhoepeni), previously thought to be mixed feeders based on taxonomic uniformitarianism and ecomorphology, were in fact browsers.

This paper expands on the work of Sponheimer et al. (1999) by adding an additional proxy measure of diet for the same seven bovid taxa, dental microwear. The primary objectives of this project are: (1) to conduct dental microwear on an extant baseline of bovids with known diets and compare these results with the dental microwear of the Makapansgat bovids, grouping the fossil taxa into dietary categories, and (2) to compare the dietary classifications based on microwear, mesowear (Schubert, in press), stable carbon isotopes, ecomorphology, and taxonomic uniformitarianism for the seven Makapansgat bovids and address the importance of these results for paleoecology.