Prairie (Microtus ochrogaster) and woodland (Microtus pinetorum) voles, which exhibit distinctly different ecological preferences (grassland versus forest), commonly co-occur in paleontological deposits in eastern North America. Despite their ecological differences, their molar morphology is similar. Assuming that those ecologic differences occurred in the past, differentiation of these two taxa is important for paleoenvironmental reconstruction. A sample of 51 lower first molars from living populations were viewed via scanning electron microscope to qualify and quantify schmelzmuster (enamel microstructure) to species-specific standards applicable to the fossil record. The most obvious differences between schmelzmuster of the two taxa are the relatively thicker bands of radial enamel on the leading edges of triangles of M. ochrogaster, as well as the consistent retention of tangential or primitive tangential enamel on the trailing edges and posterior enamel band of the posterior loop of M. pinetorum. Discriminant analysis of landmark data from the same 51 specimens established morphological boundaries for these taxa and successfully separated the recent m1s of M. ochrogaster from those of M. pinetorum. To test identification confidence from previous work, and to add an independent means of identification for future work (at any site), both techniques were applied to a sample of three-closed triangle (“M. ochrogaster” type) m1s from the late Pleistocene Wapsipinicon Local Fauna of Jones County, Iowa. Identifications of the specimens from the Wapsipinicon l.f. based on schmelzmuster and morphometric analysis are consistent with those reached using traditional morphology. Such methods serve as independent “check” of traditional (qualitative) identification, highlight new species-level characters, and quantify previously described features, for discrimination of these taxa.

No / Paleoanthropological studies often center on teeth, not only because these elements are commonly preserved in the fossil record, but because they apparently contain a wealth of information with regard to development, phylogeny, and function. However, despite a plethora of studies, somefundamental problems are still unresolved. For example, while it is recognized that the 3-dimensional arrangement of enamel prisms may hold important information with regard to phylogeny (von Koenigswald and Sander, 1997) and function (Rensberger, 2000), many paleoanthropological studies have thus far relied on investigating enamel microanatomy as a 2-dimensional structure (e.g., Dean et al., 2001 C Dean, M.G Leakey, D Reid, F Schrenk, G.T Schwartz, C Stringer and A Walker, Growth processes in teeth distinguish modern humans from Homo erectus an earlier hominins, Nature 414 (2001), pp. 628¿631. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (120)Dean et al., 2001). This is mainly due to difficulties in visualizing and quantifying the 3-D structure of prisms. In order to overcome these limitations a computer model was developed (Jiang et al., 2003) which attempted to simulate the effects of biophysical processes governing enamel formation in modern humans (adapted from Osborn, 1970). Here we extend our model and present preliminary data on inter-specific variation in prism arrangement among primates. Furthermore, during our work torecreate the 3D microstructure of prismatic enamel it became increasingly clear that there are not only limitations with previous dental growth studies, but that these studies are based on fundamentally different concepts regarding evolutionary processes from those assumed in our approach. These limitations and differences will be highlighted also.

No / Australopithecus anamensis is the stem species of all later hominins and exhibits the suite of characters traditionally associated with hominins, i.e., bipedal locomotion when on the ground, canine reduction, and thick-enameled teeth. The functional consequences of its thick enamel are, however, unclear. Without appropriate structural reinforcement, these thick-enameled teeth may be prone to failure. This article investigates the mechanical behavior of A. anamensis enamel and represents the first in a series that will attempt to determine the functional adaptations of hominin teeth. First, the microstructural arrangement of enamel prisms in A anamensis teeth was reconstructed using recently developed software and was compared with that of extant hominoids. Second, a finite-element model of a block of enamel containing one cycle of prism deviation was reconstructed for Homo, Pan, Gorilla, and A. anamensis and the behavior of these tissues under compressive stress was determined. Despite similarities in enamel microstructure between A. anamensis and the African great apes, the structural arrangement of prismatic enamel in A. anamensis appears to be more effective in load dissipation under these compressive loads. The findings may imply that this hominin species was well adapted to puncture crushing and are in some respects contrary to expectations based on macromorphology of teeth. Taking together, information obtained from both finite-element analyses and dental macroanatomy leads us to suggest that A. anamensis was probably adapted for habitually consuming a hard-tough diet. However, additional tests are needed to understand the functional adaptations of A. anamensis teeth fully.

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