Faculty Bibliography

We report here revised chronological ages at death of immature fossil hominids demonstrating for the first time that Plio-Pleistocene hominids had markedly abbreviated growth periods relative to modern man, similar to those of the modern great apes. Previous estimates of age at death for fossil hominids have principally been based on dental eruption, maturation and dental wear criteria for modern man and hence reflect their age in 'human' years. We are now able to estimate the absolute duration of permanent incisor crown formation by observing gross incremental growth features in enamel and thereby apply a timescale to dental developmental events for specimens representing four Plio-Pleistocene fossil hominid taxa. Thus we have derived more reliable-species-specific-estimates of age at death that provide a more secure model on which to base studies of the palaeodemography, growth and maturation of early hominids

High resolution replica materials are routinely used in scanning electron microscopy. A systematic evaluating procedure for replica combinations is proposed which details fourteen points to be recorded. These points include quantitative and qualitative information useful when assessing a replica combination for a particular research problem. A case study employing one silicone-based impression material and one epoxy resin is performed as an example of the procedure

Shipman and Rose (1983) have recently attracted attention to the fact that the determination of directionality of cutmarks could possibly provide additional evidence for interpretation of early hominid butchering practices and handedness. They found no criteria of directionality, however. We have previously recognized directionality in cut dental tissues and more recently in bone, and so we undertook a study of over 200 experimentally produced cutmarks on bovine bone by scanning electron microscopy. Three criteria of directionality were observed: bone smears, oblique faulting, and oblique chipping. In our analysis we considered properties of bone as a relevant variable in the microscopic appearance of cutmarks, which has also led to the new finding that not all marks made by a single tool under similar conditions are the same. We observed that bone smears occurred in most specimens, relatively low density forming bone surfaces facilitated oblique fault production, whereas oblique chipping frequently occurred in plexiform bone tissue common to growing artiodactyls. In this study, handedness of the operator could be determined from cutmarks, but much further experimental work will be required in order to detail the criteria

The experimental abrasion of forming bone surfaces was conducted so that such surfaces could be characterized. This is particularly important to bone remodeling studies utilizing scanning electron microscope (SEM) imaging of archeological material. Forming surfaces derived from subadult macaque cranial bone were treated by particle abrasion, water abrasion, sliding abrasion, brushing, manual rubbing, weight, exfoliation, chipping and replication. Acetic acid treatments were also performed. The effects of abrasive agents are specific but generally fall into rough (particle and water abrasion) and smooth (sliding abrasion, brushing, rubbing and weight) categories. Protohistoric human and Plio-Pleistocene hominid subadult craniofacial remains were observed with the SEM for comparison with experimental data. The more recent material appeared smooth, probably as a result of specimen preparation procedures using brushes. Surfaces were still interpretable as forming, however, using a more abrasion-resistant feature called intervascular ridging (IVR) described in this study. The IVR pattern is also recognized on the hominid sample, confirming the possibility of performing remodeling studies on abraded fossil material. The abrasion characteristics are somewhat more difficult to classify, however. Abrasion is defined and discussed relative to remodeling studies and taphonomy. The usefulness of the experimental data reported here, however, in paleoenvironmental reconstruction, has yet to be fully realized. Acid and mechanical preparation techniques are briefly addressed. It is concluded that it is possible to characterize a forming surface as abraded according to the findings of this study and that acid, if handled with care, will more likely preserve microanatomical surface detail. It would also be in everyone's interest to employ a less abrasive cleaning regime on archeological specimens

The histologic research on craniofacial remodeling is briefly summarized. A new methodologic approach using the scanning electron microscope (SEM) and high-resolution replicas of craniofacial bone is evaluated. Two maxillae were chosen for illustrative purposes. The specimens were replicated and prepared for routine SEM examination. In addition, a grid was applied to the replicas so that the bone growth activity states could be mapped on a coordinate system. The topographic ('T') principle is introduced as a precedent for discriminating remodeling bone growth activity states with the SEM. These activity states in vivo specify characteristic microscopic surface topographies. The three distinctive surfaces are resorptive, depository, and resting, which are mapped on a coordinate system. Results obtained are similar to those of histologic studies. The primary advantage of the SEM/replica technique is that it does not damage the specimen. This feature will facilitate more extensive investigations of craniofacial remodeling. The time and financial investments for the SEM/replica technique are significantly less than the histologic technique in the investigation of similar material. The SEM/replica technique, however, cannot be used to study nonexternal surfaces and evidence of remodeling contained within the bone cortex

Growth and development studies utilizing craniofacial skeletal material are best done by documenting evidence of the bone growth mechanisms responsible for morphogenesis. One primary mechanism is remodeling which involves coordinated bone resorption and deposition in localized areas. Some histological studies have been performed on human facial remodeling, but these studies have been limited in extent because of the destructive nature of the technique. For obvious reasons, large skeletal research collections cannot be utilized in histological work. A new technique is presented which does not damage specimens. This involves making high resolution replicas of subadult craniofacial bone which are then examined with the scanning electron microscope (SEM) for evidence of the characteristic microscopic surface topography of remodeling bone. The Topographic ('T') principle is introduced as a precedent for discriminating remodeling bone activity states with the SEM. These activity states in vivo specify characteristic microscopic surface topographies. The three distinctive surfaces are resorptive, depository, and resting. These surfaces can be mapped on a coordinate representation of the bone replica to obtain results which are similar to those of histological studies. Application of the 'T' principle and SEM/replica methodological approach offers great promise to the study of craniofacial morphogenesis

It is evident that chondrocyte determination is an example of cellular aging. This possible leads to the erroneous view that chondrocytes have a 'weak' genetic control mechanism. If such was the case, chondrocranial growth and development would be a very 'shaky' process indeed. It is recognized however that chondrocranial growth is under predominantly genetic and tissue interaction influence especially during the early phase of growth. These control factors plus other epigenetic and local environmental influences are responsible for the harmonious growth of the chondrocranium