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Recent papers by Trinkaus, Ruff, and colleagues have used a new method to estimate hominin body mass. The estimates are derived from a multiple regression of group means for body mass on stature and bi-iliac breadth in 31 male & 25 female recent human samples. The procedure produces body mass estimates very similar to those derived from femoral head diameter. With fossils, the procedure often requires the estimation of stature and bi-iliac breadth. The breadth of only one Skhul pelvis and one (perhaps two) Neandertal pelvis can be measured. Trinkaus and Ruff therefore estimated the bi-iliac breaths for the rest of the individuals in these groups by multiplying estimated stature by the ratio of bi-iliac breadth to stature of the measurable specimen. This should be reliable if within-group variability in the ratio is low; otherwise it may produce a substantial systematic error. We evaluated the procedure by measuring the bi-iliac breadth and femoral length of 35 male African Americans and 33 Inuit skeletons. The range of ratios of known biiliac breadth to estimated stature in each sample exceeded the range of Ruffs population means, and the standard deviation (SD) of the ratio within each sample was equal to or exceeded that of Ruff s population means. For single-specimen-based estimates of a mean, a ratio [+ or -] 1 SD from the group's observed mean creates a systematic bias of 6.4% - 8.0% in mass from that predicted by the measured femoral lengths and bi-iliac breadths. More importantly, individual values for the ratio in African American and Inuit data each encompass most of Ruffs population means. A sample of one will frequently produce erroneous impressions of a group's average body proportions. Paleobiological inferences should take ranges of variation and confidence limits into account whenever possible.

A Meshless Time Domain Method is used in the local support domain to solve Maxwell's equations for one-dimensional transient electromagnetic problems. The approach is based on a combination of the Meshless Radial Basis Functions and the Leapfrog time-stepping scheme for the Finite-Difference approximation of the first order partial derivatives. A comparison is performed between the conventional FDTD and RBF's with Gaussian, Wendland-C4 Compactly Supported RBF (CSRBF) and Inverse Multi-Quadric (IMQ) basis functions. The numerical results showed that the proposed method provides an accurate solution for transient electromagnetic problems. [ABSTRACT FROM AUTHOR]

The article details a study that measured molar enamel thickness in Australopithecus africanus and Paranthropus robustus by using accurate microtomographic methods to record the whole-crown distribution of enamel. The three-dimensional (3D) molar measurements showed that A. africanus enamel is relatively thinner than of recent humans and P. robustus enamel is not hyper-thick. The usefulness of the 3D distribution of enamel thickness for the interpretation of functional adaptations is also noted.

Modern humans exhibit increasing relative enamel thickness from M1 to M3. Some biomechanical (basic lever) models predict that the more distal molars in humans encounter higher occlusal forces, and it has been postulated that this provides a functional explanation for the observed gradient in relative enamel thickness. However, constrained three-dimensional models and experimental observations suggest that there is a reduction in bite force potential from M1 to M3, which would be consistent with the tendency for humans to reduce the size of the distal molars. In this regard, it has been postulated that the distal increase in enamel thickness is a consequence of crown size reduction; thus, it is unnecessary to invoke functional scenarios to explain this phenomenon. We assess these competing proposals by examining relative enamel thickness in a catarrhine primate (Papio ursinus) that exhibits crown size increase from M1 to M3. The molar row of P. ursinus is positioned relatively far forward of the temporomandibular joint, which results in the baboon being able to exert relatively greater muscle forces during posterior biting in comparison to modern humans. Thus, a significant distalward gradient of increasing enamel thickness would be expected in P. ursinus according to the hypothesis that posits it to be functionally related to bite force. The present study reveals no significant difference in relative enamel thickness along the molar row in P. ursinus. This finding lends support to the notion that the relatively thicker enamel of human distal molars is related primarily to their reduction in size. This carries potential implications for the interpretation of enamel thickness in phylogenetic reconstructions: the relatively thick molar enamel shared by modern humans and some of our fossil relatives may not be strictly homologous, in that it may result from different underlying developmental mechanisms. [ABSTRACT FROM AUTHOR]

This study presents data on the enamel thickness of deciduous (dm2) and permanent (M1–M3) molars for a geographically diverse sample of modern humans. Measurements were recorded from sections through the mesial cusps of unworn teeth. Enamel is significantly thinner on deciduous than on permanent molars, and there is a distinct trend for enamel to increase in relative thickness from M1 to M3. The relatively thicker enamel of M2s and especially M3s can be related to the overall reduction in size of more distal molar crowns, which has been attained through a differential loss of the dentine component. Enamel tends to be thicker on the protocone than on the paracone, and thicker on the protoconid than on the metaconid, but its distribution is not wholly concordant with models that predict increased thickness as a means by which to counter heavier attritional loss on these ‘functional’ cusps. Indeed, the thickness of enamel tends to be more variable on cusp tips and occlusal surfaces than over the lateral aspects of cusps. The proportionately thicker enamel over the lateral aspects of the protocone and protoconid more likely serves as a means to prolong functional crown life by preventing cusp fracture, rather than being an adaptation to increase the attritional longevity of wear facets. The present data suggest that the human dentition is not predisposed to develop a helicoidal wear plane through the disposition of molar enamel thickness. [ABSTRACT FROM AUTHOR]

Diet provides critical information about the ecology and environment of herbivores. Hence, understanding the dietary strategies of fossil herbivores and the associated temporal changes is one aspect of inferring paleoenvironmental conditions. Here, we present carbon isotope data from more than 1,050 fossil teeth that record the dietary patterns of nine herbivore families in the late Pliocene and early Pleistocene (3.6 to 1.05 Ma) from the Shungura Formation, a hominin-bearing site in southwestern Ethiopia. An increasing trend toward C 4 herbivory has been observed with attendant reductions in the proportions of browsers and mixed feeders through time. A high proportion of mixed feeders has been observed prior to 2.9 Ma followed by a decrease in the proportion of mixed feeders and an increase in grazers between 2.7 and 1.9 Ma, and a further increase in the proportion of grazers after 1.9 Ma. The collective herbivore fauna shows two major change points in carbon isotope values at ∼2.7 and ∼2.0 Ma. While hominin fossils from the sequence older than 2.7 Ma are attributed to Australopithecus , the shift at ∼2.7 Ma indicating the expansion of C 4 grasses on the landscape was concurrent with the first appearance of Paranthropus The link between the increased C 4 herbivory and more open landscapes suggests that Australopithecus lived in more wooded landscapes compared to later hominins such as Paranthropus and Homo , and has implications for key morphological and behavioral adaptations in our lineage., Competing Interests: The authors declare no competing interest.