Dental microwear analysis of extinct Flat-headed Peccary (Platygonus compressus) from Southern Indiana.

ABSTRACT. Dental microwear analysis (DMA) is a valuable means of dietary reconstruction for extant and extinct animals because it provides insight independent of dental morphology. It was employed to elucidate the diet of the extinct Late Pleistocene Flat-headed Peccary, Platygonus compressus. The study sample came from Megenity Cave in southern Indiana, which has produced the largest assemblage of P. compressus remains in the world. Ten mandibular molars were molded and replicated with resin casts following standard procedures. The molds were viewed with a scanning electron microscope at a magnification of 500x. Microscopic pits and scratches were quantified with a semi-automated software program specifically designed for microwear study. The P. compressus microwear profile was compared to profiles generated for several extant grazers, mixed feeders, and browsers. Its diet was patently intermediate in its percentage of pits (i.e., hardness) and average scratch widths (i.e., abrasiveness). Generally, its diet was more consistent with that of the browsers, although its diet was also similar to that of the mixed-feeders. By contrast, its microwear profile was not similar to the grazers. A follow-up comparison with more faunivorous animals (including suids, bats, humans, and non-human primates) indicated that the P. compressus diet is more consistent with faunivores that ate softer resources such as certain invertebrates. Overall, P. compressus had a varied diet that included a comparative balance of hard and soft as well as abrasive and non-abrasive foods.

Keywords: Pleistocene, diet, teeth

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Dental microwear analysis (DMA) is the study of microscopic pits and scratches on dental enamel created, for the most part, during mastication. Microwear-based dietary reconstructions are of particular value because they provide a means for determining diet that does not depend on dental morphology. The fact that it is non-destructive makes it useful for paleontological applications. In fact, its utility in paleontology has been demonstrated frequently. For example, DMA was used to determine the diets of Miocene giraffids, late Miocene antelope, fossil equids and rhinoceros (Solounias et al. 1988; Solounias & Hayek 1993, Fortelius & Solounias 2000; Solounias & Semprebon 2002). Additional fossil animals that have been studied via DMA include sheep (Rivals & Deniaux 2003), mammoths (Capozza 2001), primates (e.g., Teaford 1988, 1993; Ungar 1996, 1998; King 1999; Rafferty 2002; Ungar et al. 2004; Galbany 2005; Merceron et al. 2006), hominins (e.g., Grine 1981; 1987a,b; Teaford & Walker 1984; Kay & Grine 1988; Ungar & Grine 1991; Perez-Perez et al. 1999, 2003; Teaford & Ungar 2000; Grine et al. 2006; Ungar et al. 2004, 2006) and dinosaurs (e.g., Fiorillo 1991; Abler 1992; Schubert & Ungar 2005).

This study sought to determine the dental microwear profile of the extinct Flat-headed Peccary, Platygonus compressus. Most interpretations of the P. compressus gross dental morphology have suggested that it was a browser (e.g., Holman 2001). Kurten & Anderson (1980) stated that "the hypsodont teeth were adapted to chew coarse vegetation, and the dentition suggests browsing habits." Its distinction as a browser stems largely from its pronounced premolar and molar bilophodonty. The cusps are tall and evoke a zygodonty that is reminiscent of lightly-worn Mammut teeth (e.g., Janis et al. 1998). It is presumed that, like Mammut, the tall cusps were ideal for triturating hard browse and were less effective for chewing grasses. Hood & Hawksley (1975) reported "gum-line notching" on the mandibular canines that they argue probably resulted from browsing on "vegetation rich in silica or silica dust covering the vegetation." This microwear study examined the assessment that P. compressus was a browser by looking for microscopic evidence of this assertion on the molars.

Platygonus compressus was first identified in 1806 and was fully described by the mid-19th century (i.e., LeConte 1848; Leidy 1853). It stood about 760 mm high at the shoulder, was long-legged, and had a large and heavily turbinated nasal passage (Hood & Hawksley 1975; Kurten & Anderson 1980). The P. compressus dentition was more specialized than that of extant peccaries in that the incisors and canines were more gracile, the maxillary second incisor was reduced to a small peg, and I3 was lost entirely (Kurten & Anderson 1980).

Flat-headed Peccaries were widely distributed in North America during the late Pleistocene ranging from California to New York (Kurten & Anderson 1980). They also have been reported in Texas and Mexico (Slaughter 1966). In the midwestern U.S., Flat-headed Peccary are known from numerous sites, many of which are caves, including Megenity Cave and Indun Cave in Indiana, Welsh Cave in Kentucky, Sheriden Cave/Indian Trail Caverns in Ohio, Castle Rock Cave in Wisconsin, and Zoo and Bat caves in Missouri (Guilday et al. 1971; Hawksley et al. 1973; Hood & Hawksley, 1975; Richards & Munson 1988; Feldman & Hackathorn 1996; Holman 2001). These cave sites tend to produce many individuals. Zoo Cave had over 81 individuals (Hood & Hawksley 1975) while Sheriden Cave/ Indian Trail Caverns had a minimum of 39 (Feldman & Hackathorn 1996). Thirty-one individuals were recovered from Welsh Cave (Guilday et al. 1971). Megenity Cave will be discussed in greater detail later, but it has yielded hundreds of individuals and is clearly the most prolific P. compressus site in North America (Fig. 1).