Implications of outgroup selection in the phylogenetic inference of hominoids and fossil hominins.

Understanding the phylogenetic relationships among hominins and other hominoid species is critical to the study of human origins. However, phylogenetic inferences are dependent on both the character data and taxon sampling used. Previous studies of hominin phylogenetics have used Papio and Colobus as outgroups in their analyses; however, these extant monkeys possess many derived traits that may confound the polarities of morphological changes among living apes and hominins. Here, we consider Victoriapithecus and Ekembo as more suitable outgroups. Both Victoriapithecus and Ekembo are anatomically well known and are widely accepted as morphologically primitive stem cercopithecoid and hominoid taxa, respectively, making them more appropriate for inferring polarity for later-occurring hominoid- and hominin-focused analyses. Craniodental characters for both taxa were scored and then added to a previously published matrix of fossil hominin and extant hominoid taxa, replacing outgroups Papio and Colobus over a series of iterative analyses using both parsimony and Bayesian inference methods. Neither the addition nor replacement of outgroup taxa changed tree topology in any analysis. Importantly, however, bootstrap support values and posterior probabilities for nodes supporting their relationships generally increased compared to previous analyses. These increases were the highest at extant hominoid and basal hominin nodes, recovering the molecular ape phylogeny with considerably higher support and strengthening the inferred relationships among basal hominins. Interestingly, however, the inclusion of both extant and fossil outgroups reduced support for the crown hominid node. Our findings suggest that, in addition to improving character polarity estimation, including fossil outgroups generally strengthens confidence in relationships among extant hominoid and basal hominins.

Frontal sinus size in South African Later Stone Age Holocene Khoe-San.

Frontal size variation is comparatively poorly sampled among sub-Saharan African populations. This study assessed frontal sinus size in a sample of Khoe-San skeletal remains from South African Later Stone Age contexts. Volumes were determined from CT scans of 102 adult crania; individual sex could be estimated in 82 cases. Sinus volume is not sexually dimorphic in this sample. The lack of frontal sinus aplasia is concordant with the low incidences recorded for other sub-Saharan African and most other global populations save those that inhabit high latitudes. There is considerable variation in frontal sinus size among global populations, and the Khoe-San possess among the smallest. The Khoe-San have rather diminutive sinuses compared to sub-Saharan Bantu-speaking populations but resemble a northern African (Sudanese) population. Genetic studies indicate the earliest population divergence within Homo sapiens to have been between the Khoe-San and all other living groups, and that this likely occurred in Africa during the span of Marine Isotope Stages 8-6. There is scant information on frontal sinus development among Late Quaternary African fossils that are likely either closely related or attributable to Homo sapiens. Among these, the MIS 3 cranium from Hofmeyr, South Africa, exhibits distinct Khoe-San cranial affinities and despite its large size has a very small frontal sinus. This raises the possibility that the small frontal sinuses of the Holocene South African Khoe-San might be a feature retained from an earlier MIS 3 population.