Evolution of vertebral numbers in primates, with a focus on hominoids and the last common ancestor of hominins and panins.

The primate vertebral column has been extensively studied, with a particular focus on hominoid primates and the last common ancestor of humans and chimpanzees. The number of vertebrae in hominoids-up to and including the last common ancestor of humans and chimpanzees-is subject to considerable debate. However, few formal ancestral state reconstructions exist, and none include a broad sample of primates or account for the correlated evolution of the vertebral column. Here, we conduct an ancestral state reconstruction using a model of evolution that accounts for both homeotic (changes of one type of vertebra to another) and meristic (addition or loss of a vertebra) changes. Our results suggest that ancestral primates were characterized by 29 precaudal vertebrae, with the most common formula being seven cervical, 13 thoracic, six lumbar, and three sacral vertebrae. Extant hominoids evolved tail loss and a reduced lumbar column via sacralization (homeotic transition at the last lumbar vertebra). Our results also indicate that the ancestral hylobatid had seven cervical, 13 thoracic, five lumbar, and four sacral vertebrae, and the ancestral hominid had seven cervical, 13 thoracic, four lumbar, and five sacral vertebrae. The last common ancestor of humans and chimpanzees likely either retained this ancestral hominid formula or was characterized by an additional sacral vertebra, possibly acquired through a homeotic shift at the sacrococcygeal border. Our results support the 'short-back' model of hominin vertebral evolution, which postulates that hominins evolved from an ancestor with an African ape-like numerical composition of the vertebral column.

Increased variation in numbers of presacral vertebrae in suspensory mammals.

Restricted variation in numbers of presacral vertebrae in mammals is a classic example of evolutionary stasis. Cervical number is nearly invariable in most mammals, and numbers of thoracolumbar vertebrae are also highly conserved. A recent hypothesis posits that stasis in mammalian presacral count is due to stabilizing selection against the production of incomplete homeotic transformations at the lumbo-sacral border in fast-running mammals, while slower, ambulatory mammals more readily tolerate intermediate lumbar/sacral vertebrae. We test hypotheses of variation in presacral numbers of vertebrae based on running speed, positional behaviour and vertebral contribution to locomotion. We find support for the hypothesis that selection against changes in presacral vertebral number led to stasis in mammals that rely on dorsomobility of the spine during running and leaping, but our results are independent of running speed per se. Instead, we find that mammals adapted to dorsostability of the spine, such as those that engage in suspensory behaviour, demonstrate elevated variation in numbers of presacral vertebrae compared to dorsomobile mammals. We suggest that the evolution of dorsostability and reduced reliance on flexion and extension of the spine allowed for increased variation in numbers of presacral vertebrae, leading to departures from an otherwise stable evolutionary pattern.

Univariate and Linear Composite Asymmetry Statistics for the "Pair-Matching" of Bone Antimeres.

This paper examines the distributional properties of univariate and linear composite measures of long bone asymmetry. The goal of this paper is to examine models that best fit the distribution of asymmetries with implications for the improvement of forensic pair-matching techniques. We use the software R to model reference data (N = 2343) and test data (N = 71) as normal distributions, an exponential power distribution, and a skew exponential power distribution-the latter two include the normal as a special case. Our results indicate that the data best fit the latter two distributions because the data are nonnormal. We also show how asymmetry statistics that use absolute values of side differences can be fit as folded distributions. This obviates the need for empirical distributions or for transformations that attempt to convert nonnormal distributions to normal distributions. The results of this study lay the framework for improving pair-matching methods that use comparative reference data.

A newly assembled human skeletal reference collection of modern and identified Filipinos.

A collection of 75 modern skeletons from the Philippines has recently been created, and is being housed at the Archaeological Studies Program of the University of the Philippines, Diliman, Philippines. All individuals lived during the 20th century, and almost all died within the 21st century. These individuals were accessioned from exhumed and abandoned tombs at the Manila North Cemetery, and most have documented age and sex from tombstone inscriptions. This paper describes the first season of recovery and the collection's current demographic composition, with the future addition of more individuals to the collection expected to follow. The Philippines has an immediate need for forensic resources given its large vulnerable population, widespread diaspora, and exposure to natural disasters. Having a collection of modern Filipinos available for study is critical to the advancement of forensic anthropology and skeletal biology, especially for this heavily understudied population and region of the world.