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Numerous geoemydid turtle fossils from the extinct genus Echmatemys have been recovered from the middle Eocene Uinta Formation, Uinta Basin, Utah over the past several decades. Here, we tested whether co-occurring Uintan species Echmatemys callopyge and E. uintensis can be reliably differentiated based on epiplastral morphology, and whether their geospatial distributions overlapped significantly. The geographic spatial and stratigraphic distributions of Uinta Basin E. callopyge and E. uintensis specimens were compared using ArcGIS and analysis of variance (ANOVA). The analysis revealed overlapping geographic distributions of these two species, and no significant differences in stratigraphic dispersal. This finding of extensive geospatial overlap between the two Uintan Echmatemys species highlights the need for accurate taxonomic identification, such as the gular scale morphology validated here. In addition, we sought to address a methodological question regarding the relative efficacy of data complexity in this context. Using epiplastra from three additional Eocene species of Echmatemys, we employed hierarchical analyses of increasing data complexity, from standard linear dimensions to 2D geometric morphometrics to 3D laser scans, to determine the degree to which data complexity contributes to taxonomic assessments within this genus. Uintan species E. callopyge and E. uintensis were found to differ significantly in epiplastral shape as captured by all three categories of data. These findings verify that these two co-occurring species can be differentiated consistently using the shape of the gular scale, and that the use of geometric morphometrics can improve identification of fragmentary specimens. Among the non-Uintan species, dorsal and ventral 2D landmark data reliably differentiated among species, but the linear dimensions were less useful.

The relationship between the structure and function of the primate apical tuft is poorly understood. This study addresses several hypotheses about apical tuft morphology using a large modern primate comparative sample. Two indices of tuft size are employed: expansion and robusticity. First, comparisons of relative apical tuft size were drawn among extant nonhuman primate groups in terms of locomotion and phylogenetic category. Both of these factors appear to play a role in apical tuft size among nonhuman primates. Suspensory primates and all platyrrhines had the smallest apical tufts, while terrestrial quadrupeds and all strepsirrhines (regardless of locomotor category) had the largest tufts. Similarly, hypotheses regarding the apical tufts of hominins, especially the large tufts of Neandertals were addressed using a comparison of modern warm- and cold-adapted humans. The results showed that cold-adapted populations possessed smaller apical tufts than did warm-adapted groups. Therefore, the cold-adaptation hypothesis for Neandertal distal phalangeal morphology is not supported. Also, early modern and Early Upper Paleolithic humans had apical tufts that were significantly less expanded and less robust than those of Neandertals. The hypothesis that a large apical tuft serves as support for an expanded digital pulp is supported by radiographic analysis of modern humans in that a significant correlation was discovered between the width of the apical tuft and the width of the pulp. The implications of these findings for hypotheses about the association of apical tuft size and tool making in the hominin fossil record are discussed. KEY WORDS distal phalanges; locomotion; phylogeny; primates; Neandertal

Temporal bone shape has been shown to reflect molecular phylogenetic relationships among hominoids and offers significant morphological detail for distinguishing taxa. Although it is generally accepted that temporal bone shape, like other aspects of morphology, has an underlying genetic component, the relative influence of genetic and environmental factors is unclear. To determine the impact of genetic differentiation and environmental variation on temporal bone morphology, we used three-dimensional geometric morphometric techniques to evaluate temporal bone variation in 11 modern human populations. Population differences were investigated by discriminant function analysis, and the strength of the relationships between morphology, neutral molecular distance, geographic distribution, and environmental variables were assessed by matrix correlation comparisons. Significant differences were found in temporal bone shape among all populations, and classification rates using cross-validation were relatively high. Comparisons of morphological distances to molecular distances based on short tandem repeats (STRs) revealed a significant correlation between temporal bone shape and neutral molecular distance among Old World populations, but not when Native Americans were included. Further analyses suggested a similar pattern for morphological variation and geographic distribution. No significant correlations were found between temporal bone shape and environmental variables: temperature, annual rainfall, latitude, or altitude. Significant correlations were found between temporal bone size and both temperature and latitude, presumably reflecting Bergmann's rule. Thus, temporal bone morphology appears to partially follow an isolation by distance model of evolution among human populations, although levels of correlation show that a substantial component of variation is unexplained by factors considered here. KEY WORDS geometric morphometrics; molecular distance; cranial morphology