Using BayesModelS to provide Bayesian- and phylogenetically-informed primate body mass predictions

An accurate prediction of the body mass of an extinct species can greatly inform the reconstruction of that species' ecology. Therefore, paleontologists frequently predict the body mass of extinct taxa from fossilized materials, particularly dental dimensions. Body mass prediction has traditionally been performed in a frequentist statistical framework, and accounting for phylogenetic relationships while calibrating prediction models has only recently become more commonplace. In this article, we apply BayesModelS-a phylogenetically informed Bayesian prediction method-to predict body mass in a sample of 49 euarchontan species (24 strepsirrhines, 20 platyrrhines, 3 tarsiids, 1 dermopteran, and 1 scandentian) and compare this approach's body mass prediction accuracy with other commonly used techniques, namely ordinary least squares, phylogenetic generalized least squares, and phylogenetic independent contrasts (PICs). When predicting the body masses of extant euarchontans from dental and postcranial variables, BayesModelS and PICs have substantially higher predictive accuracy than ordinary least squares and phylogenetic generalized least squares. The improved performances of BayesModelS and PIC are most evident for dentally derived body mass proxies or when body mass proxies have high degrees of phylogenetic covariance. Predicted values generated by BayesModelS and PIC methods also show less variance across body mass proxies when applied to the Eocene adapiform Notharctus tenebrosus. These more explicitly phylogenetically based methods should prove useful for predicting body mass in a paleontological context, and we provide executive scripts for both BayesModelS and PIC to increase ease of application.

Patterns and magnitudes of craniofacial covariation in extant cercopithecids

The cranium contains almost all of the vertebrate sensory organs and plays an essential role in vertebrate evolution. Research on the primate cranium has revealed that it is both highly integrated and modular, but studies have historically focused on covariance between the neurocranium and facial skeleton rather than on bones specific to special senses such as vision. The goal of this work is to investigate patterns and magnitudes of craniofacial covariation in extant cercopithecids with particular attention to the orbits. This study takes a quantitative approach using data collected from 38 homologous cranial landmarks across 11 genera of cercopithecid monkeys (Cercopithecidae, N = 291). These data demonstrate that both patterns and magnitudes of craniofacial covariation differ across Cercopithecidae at subfamily, tribe, and genus levels, with the strongest integration in the papionins (and specifically Papio) and significantly weaker covariation in the colobines, particularly Presbytis. Orbital height does not covary with other measurements of the cranium to the same degree as other cranial traits in Cercopithecidae and is highly constrained across the family. This study has important implications for our understanding of the evolution and development of morphological diversity in the cercopithecid cranium and evolution of the primate eye. This study also highlights the potential error of broad assumptions about generalizing patterns and magnitudes of modularity and integration across primates. Additionally, these findings reiterate the importance of trait selection for interpreting fossil taxonomy, as craniofacial covariation may impact phenotypes commonly used to differentiate fossil primate species.

Comparison of 14 body size variables on adult skeletal age methods: how body mass, BMI, fat and muscle influence age estimations

Background: Skeletal age estimations consistently under-age individuals with low body mass and over-age individuals with high body mass.Aim: To assess the directional biases of body size variables, including fat and muscle tissue, on skeletal age estimates.Subjects and methods: CT scans of 420 age- and size-selected cadavers were assessed using the fourth rib and pubic symphysis age estimation methods. MANCOVA was used to test the effects of stature, body mass, circumference, and fat and muscle tissue area on age estimation biases.Results: For both methods, there were biases based on body mass, BMI, circumference and fat tissue area. Individuals with the lowest measurements for these variables were under-aged while individuals with the highest measurements were over-aged. Age estimation biases were not affected by stature, muscle area, or skeletal measurements of bi-iliac breadth, femoral head diameter, or femoral length.Conclusion: Increased body mass, and specifically fat tissue, accelerates skeletal ageing. Increased muscle area generally did not show a protective effect on skeletal ageing. The accuracy of age estimations would be improved by factoring in body mass. However, femoral head diameter and bi-iliac breadth are not good proxies for body mass. Osteological markers of obesity offer a promising new approach.

Discrepancies between reported and cadaveric body size measurements associated with a modern donated skeletal collection

Body mass and stature estimation methods used in biological anthropology require materials with known body size information. There are several types of body size data that can be associated with skeletal collections. However, discussion regarding the reliability and suitability of these types of information for anthropological research is scarce. This paper focuses on differences between reported and recorded cadaver weights and heights associated with a modern donated skeletal collection, similar to these commonly used in anthropological research. In addition, the study identifies factors that may influence these discrepancies. The results show statistically significant differences between reported and cadaver body size information. Generally, reported weights, statures and body mass indices (BMI) were greater compared to the cadaver information in this sample. However, potential effects on these discrepancies varied depending on sex and information type. Age was found to influence stature discrepancy in females, and donation type had an effect on the female weight discrepancy. The results also show that body size range (weight, stature and BMI) can contribute to these discrepancies. Even though the differences between reported and cadaver data may not be significant at the population level, the individual variation can cause misclassifications of individuals depending on the data used. This study encourages researchers using modern documented collections and their body size information to openly acknowledge the types of weight and stature data used and to discuss potential problems associated with them.

Virtual anthropology - a brief review of the literature and history of computed tomography

Computed tomography (CT) has influenced numerous fields since its inception in the 1970s. The field of palaeoanthropology significantly benefited from this efficient and non-invasive medium in terms of the conservation, reconstruction and analysis of fossil human remains. Over the past decade, there has been a steady increase in the number of forensic anthropological studies incorporating virtual osteological analyses. Because of the increasing importance of these modern cross-sectional imaging techniques and the requirement for standardized parameters in forensic science, we deemed it important to outline the history and development of CT applications in these related academic areas. The present paper outlines the history of “virtual anthropology” and osteological multi-detector CT in the context of palaeoanthropology and forensic anthropology.

Body mass estimates of hominin fossils and the evolution of human body size

Body size directly influences an animal's place in the natural world, including its energy requirements, home range size, relative brain size, locomotion, diet, life history, and behavior. Thus, an understanding of the biology of extinct organisms, including species in our own lineage, requires accurate estimates of body size. Since the last major review of hominin body size based on postcranial morphology over 20 years ago, new fossils have been discovered, species attributions have been clarified, and methods improved. Here, we present the most comprehensive and thoroughly vetted set of individual fossil hominin body mass predictions to date, and estimation equations based on a large (n = 220) sample of modern humans of known body masses. We also present species averages based exclusively on fossils with reliable taxonomic attributions, estimates of species averages by sex, and a metric for levels of sexual dimorphism. Finally, we identify individual traits that appear to be the most reliable for mass estimation for each fossil species, for use when only one measurement is available for a fossil. Our results show that many early hominins were generally smaller-bodied than previously thought, an outcome likely due to larger estimates in previous studies resulting from the use of large-bodied modern human reference samples. Current evidence indicates that modern human-like large size first appeared by at least 3-3.5 Ma in some Australopithecus afarensis individuals. Our results challenge an evolutionary model arguing that body size increased from Australopithecus to early Homo. Instead, we show that there is no reliable evidence that the body size of non-erectus early Homo differed from that of australopiths, and confirm that Homo erectus evolved larger average body size than earlier hominins.