Computed tomography and the measurement of enamel thickness in extant hominoids: implications for its palaeontological application

Isolated permanent lower molars of Homo sapiens, Pan troglodytes and Gorilla gorilla were imaged by computed tomography (CT) using a 1,5 mm thick section through the mesial cusps. The teeth were examined dry and immersed in water. Measurements of enamel thickness were made on enlargements of hard copy images. Following CT examination, the crowns were sectioned in the same plane, and the cut faces with maximum dentine content were micrographed for measurement using a scanning electron microscope (SEM). Enamel thickness measurements from the CT images were noticeably exaggerated compared to the ideal (sectioned) values, and the CT values for dry specimen images were even larger than those for wet specimen images. These results indicate that CT cannot be employed to measure enamel thickness with any degree of reliability in modem specimens. There is no close correspondence between the SEM and CT values; therefore, the latter cannot even be used to predict the actual values. Thus, the application of CT in the measurement of enamel thickness in fossils is rather dubious.National Science Foundation NSF BNS-89869

Postcanine tooth function and jaw movement in the gomphodont cynodont Diademodon (Reptilia; Therapsida)

Main articleThe postcanine dentition of Diademodon was well adapted, in both morphology and pattern of replacement, to exercising and maintaining precise occlusion. These teeth may be grouped into three morphological classes, consisting of conical, gomphodont and sectorial teeth. The anterior conicals may have acted as gripping teeth, and the posterior sectorials may have been utilized as food "tenderizers" or shredders, while the intermediate gomphodont teeth were utilized in the mastication of food items. The gomphodont teeth, which show evidence of heavy wear, were examined in the scanning electron microscope (SEM), in order to attempt a reconstruction of the masticatory jaw movements in this animal, based on the morphology and orientation of the occlusal wear facets. The occlusal surfaces of the gomphodont teeth are pitted. The pitted occlusal surface texture is an indication of either abrasion or attrition, resulting from direct pounding of the lower teeth against their maxillary antagonists. It is concluded that masticatory jaw movements in Diademodon were wholly orthal. There is no dental evidence to support the contention that this reptile exercised either propalinal (Hopson, 1971) or ectental chewing movements. The jaw closing action in Diademodon appears to have been equivalent to the masticatory power stroke.The Medical Referees' Fund of the Department of Anatomy, University of the Witwatersrand

Quantitative Analysis of Occlusal Microwear in Australopithecus and Paranthropus

Quantitative analysis of microwear features preserved on the occlusal surfaces of the M2s of southern African specimens of Australopithecus and Paranthropus (the so-called \u27gracile\u27 and \u27robust\u27 australopithecines) reveals that there is no striking relationship in either taxon between occlusal facet inclination and the incidence of wear features. Within each taxon, Phase I and Phase II facets tend to differ in a similar manner in the total number of wear features, the percentage frequency of pitting, and in the orientation of wear scratches. Nevertheless, Paranthropus molars tend to display significantly greater numbers of microwear features on both Phase I and II facets than do Australopithecus homologues, and Paranthropus molars also evince significantly higher proportions of occlusal pitting on these surfaces. Paranthropus and Australopithecus crowns also differ significantly in the degree by which the occlusal wear scratches vary in their orientation. On each facet, Australopithecus tooth scratches display a greater degree of directional similarity. The differences between the Phase I and Phase II facets of Australopithecus and Paranthropus M2s suggest that the dietary items involved in the production of these observed patterns differed also. The diets of these Plio-Pleistocene hominids appear to have been qualitatively dissimilar

Scanning Electron Microscopy of Early Dinosaur Egg Shell Structure: A Comparison with Other Rigid Sauropsid Eggs

Fossil eggs attributable to dinosaur (probably prosauropod) parentage that have been recovered from the early Jurassic Elliot Formation sediments at the Rooidraai locality possess shells that are similar to those of birds and crocodilians, and distinctly unlike those of chelonians and gekkonids. The preserved shell is very thin, and distinct mammillary processes are lacking, although the inner surface displays an undulating contour. The absence of these processes may be attributable to the inner portion of the shell having been at least partially decalcified during incubation and not preserved in the fossil state. The shells appear to be composed of broadly wedge-shaped, albeit ill-defined calcareous units, and they are similar to those of birds and other dinosaurs in the pattern of cleavage shown by the tabular calcite crystals of the palisade layer, and in the absence of the dominant horizontal lamellae that characterize crocodilian shells. The differential resemblance of these early Jurassic shells to the eggs of other closely related sauropsid taxa may be pertinent to questions concerning the evolution of egg shell structure within this clade

Clarifying Relationships Between Cranial Form and Function in Tapirs, With Implications for the Dietary Ecology of Early Hominins

Paleontologists and paleoanthropologists have long debated relationships between cranial morphology and diet in a broad diversity of organisms. While the presence of larger temporalis muscle attachment area (via the presence of sagittal crests) in carnivorans is correlated with durophagy (i.e. hard-object feeding), many primates with similar morphologies consume an array of tough and hard foods—complicating dietary inferences of early hominins. We posit that tapirs, large herbivorous mammals showing variable sagittal crest development across species, are ideal models for examining correlations between textural properties of food and sagittal crest morphology. Here, we integrate dietary data, dental microwear texture analysis, and finite element analysis to clarify the functional significance of the sagittal crest in tapirs. Most notably, pronounced sagittal crests are negatively correlated with hard-object feeding in extant, and several extinct, tapirs and can actually increase stress and strain energy. Collectively, these data suggest that musculature associated with pronounced sagittal crests—and accompanied increases in muscle volume—assists with the processing of tough food items in tapirs and may yield similar benefits in other mammals including early hominins

Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei

The Plio-Pleistocene hominin Paranthropus boisei had enormous, flat, thickly enameled cheek teeth, a robust cranium and mandible, and inferred massive, powerful chewing muscles. This specialized morphology, which earned P. boisei the nickname “Nutcracker Man”, suggests that this hominin could have consumed very mechanically challenging foods. It has been recently argued, however, that specialized hominin morphology may indicate adaptations for the consumption of occasional fallback foods rather than preferred resources. Dental microwear offers a potential means by which to test this hypothesis in that it reflects actual use rather than genetic adaptation. High microwear surface texture complexity and anisotropy in extant primates can be associated with the consumption of exceptionally hard and tough foods respectively. Here we present the first quantitative analysis of dental microwear for P. boisei. Seven specimens examined preserved unobscured antemortem molar microwear. These all show relatively low complexity and anisotropy values. This suggests that none of the individuals consumed especially hard or tough foods in the days before they died. The apparent discrepancy between microwear and functional anatomy is consistent with the idea that P. boisei presents a hominin example of Liem's Paradox, wherein a highly derived morphology need not reflect a specialized diet

Frontal sinuses and human evolution

The frontal sinuses are cavities inside the frontal bone located at the junction between the face and the cranial vault and close to the brain. Despite a long history of study, understanding of their origin and variation through evolution is limited. This work compares most hominin species’ holotypes and other key individuals with extant hominids. It provides a unique and valuable perspective of the variation in sinuses position, shape, and dimensions based on a simple and reproducible methodology. We also observed a covariation between the size and shape of the sinuses and the underlying frontal lobes in hominin species from at least the appearance of Homo erectus. Our results additionally undermine hypotheses stating that hominin frontal sinuses were directly affected by biomechanical constraints resulting from either chewing or adaptation to climate. Last, we demonstrate their substantial potential for discussions of the evolutionary relationships between hominin species

Regional human anatomy : a laboratory workbook for ...

xiv, 415 p. : ilus. ; 26 cm

Regional human anatomy : a laboratory workbook for ...

xiv, 415 p. : ilus. ; 28 cm

Regional Human Anantomy : A Laboratory Workbook for Use with Models and Prosections (second edition )

xiv + 416 hl hlm., 27.5 cm.