Degenerative variance on age-related traits from pelvic bone articulations and its implication for age estimation.

Age at death estimation methods, when applied to skeletal remains of adults, have provided inaccurate results. These aging methods often depend on observations of the degenerative changes occurring at specific articulations, however, the effects of the aging process on the human skeleton are only partially known. Therefore a need exists to increase our understanding about the age related metamorphosis process to improve aging methods. The aim of this study is to determine which age-related traits observable on the pelvic bone articulations are correlated and to quantify their shared degenerative variance. Thus it is intended to quantify the degenerative relationship among features within each pelvic joint. Fifteen age related traits were analyzed for the pubic symphysis, eight traits for the auricular surface of the ilium, and six traits for the acetabulum. Age-related traits from the pelvic joints were recorded on adult skeletons from two reference collections the William Bass Donated Skeletal Collection and the Coimbra Collection. A Principal Components Analysis, partial correlation controlling for age, and a Kendall's W coefficient of concordance were calculated to determine the level of dependence among traits. A similar pattern of correlation amongst traits was obtained for both collections. Some of the traits shared a high to moderate correlation. However, some features, such as dense bone at the auricular surface, possessed a high independence from other traits. Results suggest that age estimation methods should take into consideration how age-related traits correlate and their level of dependence, which may possibly assist in the establishment of more effective scoring systems in new and revised age at death estimation methods.

Epiphyseal fusion and dental development in Pan paniscus with comparisons with Pan troglodytes.

OBJECTIVES: Compared with frequent studies of skeletal development in chimpanzees, relatively little is known about bonobo skeletal development. This study seeks to explore the relationship between skeletal and dental development in both species of Pan. New data are presented for fusion sites not previously observed in bonobos. MATERIALS AND METHODS: In a sample of 34 Pan paniscus and 168 Pan troglodytes subadults, state of fusion was recorded for 30 epiphyseal fusion sites using a three-stage system of unfused, midfusion, and complete fusion based on Wintheiser, Clauser, and Tappen. Stage of dental development for permanent mandibular dentition was assessed using the Demrijian, Goldstein, and Tanner method. These data allowed for comparisons of both species of Pan and the two subspecies of P. troglodytes. RESULTS: The sequence of fusion events was generally consistent between the two species, but some exceptions may exist for the knee and ankle. The number of fusion events that occurred after complete dental mineralization was similar in both species. No statistically significant differences were found in the fusion timing for the subspecies of P. troglodytes. DISCUSSION: Bolter and Zihlman suggested that fusion at the acetabulum occurs earlier in Pan paniscus, while fusion of epiphyses at the knee are delayed, compared with P. troglodytes. Our data do not indicate earlier fusion of the acetabulum, but fusion events at the knee may complete later relative to dental mineralization in Pan pansicus. Compared with Homo sapiens, both P. troglodytes and Pan paniscus demonstrate later completion of epiphyseal fusion relative to dental mineralization.

A new multivariate method for determining sex of immature human remains using the maxillary first molar.

OBJECTIVES: This study investigated the use of sexually dimorphic metrics of the first permanent maxillary molar (M1 ) to determine sex in adult and immature individuals within and between populations. METHODS: Ten M1 dimensions were measured in 91 adults (19-55 years) and 58 immatures (5-18 years) from two English populations, one of documented sex (Spitalfields crypt) and another of morphologically-assigned sex (Black Gate). Preliminary statistical analysis was undertaken to explore bilateral differences and variation by age and sex, followed by multivariate analyses to predict sex from dental metrics. RESULTS: Both cross-validated linear discriminant analysis and binary logistic regression predicted biological sex consistent with known sex in 94.6% of adults and 90.9% of immatures. When functions extracted from the Spitalfields data were used to assign sex to Black Gate adults, consistency with morphological sex varied from 83.3% to 57.7%. A new function developed on Black Gate resulted in only a 4.8% increase in maximum accuracy but reduced bias. The immature cohort comprised 19 (52.8%) males and 17 (47.2%) females. CONCLUSIONS: This study demonstrates substantial sexual dimorphism in a single tooth which is commonly preserved in archaeological and forensic contexts. It successfully assigns biological sex to immatures from 5 years of age with substantially greater accuracy than any other morphological or metric method. We suggest that accurate cross-population functions based on dentition require a trade-off between accuracy and applicability, and that functions extracted from populations of documented sex can be used to assign sex to other archaeological and forensic remains.

Experimental taphonomy: post-mortem microstructural modifications in Sus scrofa domesticus bone.

Bone is a highly specialised form of hard and rigid connective tissue whose histological structure undergoes post-mortem modifications. In taphonomic research, histological examination of bone thin sections is used to investigate these post-mortem microstructural changes in skeletal tissues. In this study, diagenetic modifications in pig skeletal remains (Sus scrofa domesticus) which were exposed to different taphonomic conditions as part of a long-term, real-time experiment were examined under light microscope (i.e. plain and cross polarized light). This experiment demonstrated that macroscopic appearance and microscopic preservation of bone may significantly differ. Early microbial attack was identified as enlarged osteocyte lacunae that later coalesce to constitute larger foci. Additionally, microscopic preservation of different skeletal elements varied intra-individually, while within bone differential preservation (i.e. proximal versus distal ends) was also observed. However, no specific patterns of early histological attack (e.g. endosteal and periosteal destruction) and no clear relationship between histological preservation and proximity to the abdominal area were detected. Lastly, the presence and composition of protective textiles had a clear effect on bone preservation. This research project, therefore, provided important evidence for the better understanding of the diagenetic processes that occur within bones whilst buried or exposed on the ground surface.

Epiphyseal fusion in Pan troglodytes relative to dental age.

Previous studies on different aspects of chimpanzee growth and development have documented dental eruption and development, long bone and somatic growth, and to a lesser extent, skeletal fusion. Such data are useful in comparative and evolutionary studies of growth and some aspects of life history evolution in apes and early hominids. However, few studies have integrated dental development and other aspects of skeletal development, and none of these have been able to incorporate a large study sample. This study documents dental mineralization and skeletal epiphyseal fusion in a mixed-sex sample of 155 Pan troglodytes skeletons, and aims to: a) document the pattern of dental and skeletal developmental in chimpanzees; b) compare male and female developmental patterns in chimpanzees; and c) compare these chimpanzee developmental patterns to general patterns of dental and skeletal development in published human studies. The analysis of both dental and skeletal development in this sample demonstrates clearly that dental development is complete before the fusion of the many skeletal epiphyses, in contrast to the pattern observed in humans. Age estimates for individuals were calculated using previously published regression equations for dental development and used to estimate fusion ages. These appear to be accurate in that our estimates are similar to published ranges. These data improve our understanding about chimpanzee dental and skeletal development and provide a basis for further comparison between extant apes and humans, as well as those extinct species represented by fossil partial skeletons.

Handedness in captive gorillas (Gorilla gorilla).

Species-level right handedness is frequently presented as a marker of human uniqueness. Handedness also has implications for the evolution of language and cognition. In this study, we examined handedness in 22 captive gorillas (Gorilla gorilla) across a range of behaviours that were part of their daily routine. Ten individuals showed no preferences for any of the behaviours performed, and the majority of the remaining individuals showed a preference for only one behaviour. These results lend support to the theory that species-level handedness is unique to humans. It is hoped that these results will contribute to investigations into the evolution of handedness, which can ultimately be used to further our understanding of the evolution of human language and cognition.

Handedness in captive bonobos (Pan paniscus).

Species level right-handedness is often considered to be unique to humans. Handedness is held to be interrelated to our language ability and has been used as a means of tracing the evolution of language. Here we examine handedness in 3 captive groups of bonobos (Pan paniscus) comprising 22 individuals. We found no evidence for species level handedness. Conclusions that can be drawn from these findings are: (1) species level handedness evolved after the divergence of the Pan and Homo lineages; (2) inconsistent preferences may represent precursors to human handedness, and (3) Pan may have language abilities but these cannot be measured using handedness.

Dental microwear in anubis and hybrid baboons (Papio hamadryas, sensu lato) living in Awash National Park, Ethiopia.

We describe dental microwear in baboons (Papio hamadryas sensu lato) from the anubis-hamadryas hybrid zone of Awash National Park, Ethiopia, outline its variation with sex and age, and attempt to relate the observed microwear pattern to environment and diet. Casts of the maxillary second molar of 52 adult and subadult individuals of both sexes were examined with a scanning electron microscope at x 500. Digitized micrographs were taken at a consistent location on facet 9, and microwear was recorded with an image analysis software package. Univariate and multivariate statistics were used to investigate the shape, size, and density of microwear features. The overall pattern of microwear exhibits an unusual combination of high feature density, with numerous small pits and relatively wide striations, and a high correlation between width of pits and striations across individuals. We interpret this pattern as predominantly the consequence of abrasion by relatively small-caliber environmental grit when accidentally ingested with tough foods such as dried seeds and fruits, as expected in a terrestrial omnivore living in a dusty habitat. Statistical analysis revealed no significant differences between groups defined by sex, age, or troop membership, a result consistent with qualitative observations of feeding habits in this population, and which lends no support to the hypothesis that the longer jaws of adult males should result in longer striations. A trend towards greater feature density in females, however, might be due to limited sexual dinichism, and merits further investigation.