Cross-sectional data accurately model longitudinal growth in the craniofacial skeleton.

Dense, longitudinal sampling represents the ideal for studying biological growth. However, longitudinal samples are not typically possible, due to limits of time, prohibitive cost, or health concerns of repeat radiologic imaging. In contrast, cross-sectional samples have few such drawbacks, but it is not known how well estimates of growth milestones can be obtained from cross-sectional samples. The Craniofacial Growth Consortium Study (CGCS) contains longitudinal growth data for approximately 2000 individuals. Single samples from the CGCS for individuals representing cross-sectional data were used to test the ability to predict growth parameters in linear trait measurements separately by sex. Testing across a range of cross-sectional sample sizes from 5 to the full sample, we found that means from repeated samples were able to approximate growth rates determined from the full longitudinal CGCS sample, with mean absolute differences below 1 mm at cross-sectional sample sizes greater than ~ 200 individuals. Our results show that growth parameters and milestones can be accurately estimated from cross-sectional data compared to population-level estimates from complete longitudinal data, underscoring the utility of such datasets in growth modeling. This method can be applied to other forms of growth (e.g., stature) and to cases in which repeated radiographs are not feasible (e.g., cone-beam CT).

Oldest evidence of abundant C4 grasses and habitat heterogeneity in eastern Africa.

The assembly of Africa's iconic C4 grassland ecosystems is central to evolutionary interpretations of many mammal lineages, including hominins. C4 grasses are thought to have become ecologically dominant in Africa only after 10 million years ago (Ma). However, paleobotanical records older than 10 Ma are sparse, limiting assessment of the timing and nature of C4 biomass expansion. This study uses a multiproxy design to document vegetation structure from nine Early Miocene mammal site complexes across eastern Africa. Results demonstrate that between ~21 and 16 Ma, C4 grasses were locally abundant, contributing to heterogeneous habitats ranging from forests to wooded grasslands. These data push back the oldest evidence of C4 grass-dominated habitats in Africa-and globally-by more than 10 million years, calling for revised paleoecological interpretations of mammalian evolution.

The evolution of hominoid locomotor versatility: Evidence from Moroto, a 21 Ma site in Uganda.

Living hominoids are distinguished by upright torsos and versatile locomotion. It is hypothesized that these features evolved for feeding on fruit from terminal branches in forests. To investigate the evolutionary context of hominoid adaptive origins, we analyzed multiple paleoenvironmental proxies in conjunction with hominoid fossils from the Moroto II site in Uganda. The data indicate seasonally dry woodlands with the earliest evidence of abundant C4 grasses in Africa based on a confirmed age of 21 million years ago (Ma). We demonstrate that the leaf-eating hominoid Morotopithecus consumed water-stressed vegetation, and postcrania from the site indicate ape-like locomotor adaptations. These findings suggest that the origin of hominoid locomotor versatility is associated with foraging on leaves in heterogeneous, open woodlands rather than forests.

Giant dwarf crocodiles from the Miocene of Kenya and crocodylid faunal dynamics in the late Cenozoic of East Africa.

We describe two new osteolaemine crocodylids from the Early and early Middle Miocene of Kenya: Kinyang mabokoensis tax. nov. (Maboko, 15 Ma) and Kinyang tchernovi tax. nov. (Karungu and Loperot, 18 Ma). Additional material referable to Kinyang is known from Chianda and Moruorot. The skull was broad and dorsoventrally deep, and the genus can be diagnosed based on the combined presence of a partial overbite, a subdivided fossa for the lateral collateral ligament on the surangular, and a maxilla with no more than 13 alveoli. Phylogenetic analyses based on morphological and combined morphological and molecular data support a referral of Kinyang to Osteolaeminae, and morphological data alone put the new taxon at the base of Euthecodontini. Some Kinyang maxillae preserve blind pits on the medial caviconchal recess wall. Kinyang co-occurs with the osteolaemine Brochuchus at some localities, and together, they reinforce the phylogenetic disparity between early Neogene osteolaemine-dominated faunas and faunas dominated by crocodylines beginning in the Late Miocene in the Kenya Rift. The causes of this turnover remain unclear, though changes in prevailing vegetation resulting from tectonic and climatic drivers may provide a partial explanation.

Craniofacial growth and morphology among intersecting clinical categories.

Differential patterns of craniofacial growth are important sources of variation that can result in skeletal malocclusion. Understanding the timing of growth milestones and morphological change associated with adult skeletal malocclusions is critical for developing individualized orthodontic growth modification strategies. To identify patterns in the timing and geometry of growth, we used Bayesian modeling of cephalometrics and geometric morphometric analyses with a dense, longitudinal sample consisting of 15,407 cephalograms from 1,913 individuals between 2 and 31 years of age. Individuals were classified into vertical facial types (hyper-, normo-, hypo-divergent) and anteroposterior (A-P) skeletal classes (Class I, Class II, Class III) based on adult mandibular plane angle and ANB angle, respectively. These classifications yielded eight facial type-skeletal class categories with sufficient sample sizes to be included in the study. Four linear cephalometrics representing facial heights and maxillary and mandibular lengths were fit to standard double logistic models generating type-class category-specific estimates for age, size, and rate of growth at growth milestones. Mean landmark configurations were compared among type-class categories at four time points between 6 and 20 years of age. Overall, morphology and growth patterns were more similar within vertical facial types than within A-P classes and variation among A-P classes typically nested within variation among vertical types. Further, type-class-associated variation in the rate and magnitude of growth in specific regions identified here may serve as targets for clinical treatment of complex vertical and A-P skeletal malocclusion and provide a clearer picture of the development of variation in craniofacial form.

Estimating Craniofacial Growth Cessation: Comparison of Asymptote- and Rate-Based Methods.

OBJECTIVE: To identify differences between asymptote- and rate-based methods for estimating age and size at growth cessation in linear craniofacial measurements. DESIGN: This is a retrospective, longitudinal study. Five linear measurements were collected from lateral cephalograms as part of the Craniofacial Growth Consortium Study (CGCS). Four estimates of growth cessation, including 2 asymptote- (GCasym, GCerr) and 2 rate-based (GCabs, GC10%) methods, from double logistic models of craniofacial growth were compared. PARTICIPANTS: Cephalometric data from participants in 6 historic longitudinal growth studies were included in the CGCS. At least 1749 individuals (870 females, 879 males), unaffected by craniofacial anomalies, were included in all analyses. Individuals were represented by a median of 11 images between 2.5 and 31.3 years of age. RESULTS: GCasym consistently occurred before GCerr and GCabs consistently occurred before GC10% within the rate-based approaches. The ordering of the asymptote-based methods compared to the rate-based methods was not consistent across measurements or between males and females. Across the 5 measurements, age at growth cessation ranged from 13.56 (females, nasion-basion, GCasym) to 24.39 (males, sella-gonion, GCerr). CONCLUSIONS: Adolescent growth cessation is an important milestone for treatment planning. Based on our findings, we recommend careful consideration of specific definitions of growth cessation in both clinical and research settings since the most appropriate estimation method may differ according to patients' needs. The different methods presented here provide useful estimates of growth cessation that can be applied to raw data and to a variety of statistical models of craniofacial growth.

Geometric morphometric analysis of growth patterns among facial types.

INTRODUCTION: Extreme patterns of vertical facial divergence are of great importance to clinicians because of their association with dental malocclusion and functional problems of the orofacial complex. Understanding the growth patterns associated with vertical facial divergence is critical for clinicians to provide optimal treatment. This study evaluates and compares growth patterns from childhood to adulthood among 3 classifications of vertical facial divergence using longitudinal, lateral cephalograms from the Craniofacial Growth Consortium Study. METHODS: Participants (183 females, 188 males) were classified into 1 of 3 facial types on the basis of their adult mandibular plane angle (MPA): hyperdivergent (MPA >39°; n = 40), normodivergent (28° ≤ MPA ≤ 39°; n = 216), and hypodivergent (MPA <28°; n = 115). Each individual had 5 cephalograms between ages 6 and 20 years. A set of 36 cephalometric landmarks were digitized on each cephalogram. Landmark configurations were superimposed to align 5 homologous landmarks of the anterior cranial base and scaled to unit centroid size. Growth trajectories were calculated using multivariate regression for each facial type and sex combination. RESULTS: Divergent growth trajectories were identified among facial types, finding more similarities in normodivergent and hypodivergent growth patterns than either share with the hyperdivergent group. Through the use of geometric morphometric methods, new patterns of facial growth related to vertical facial divergence were identified. Hyperdivergent growth exhibits a downward rotation of the maxillomandibular complex relative to the anterior cranial base, in addition to the increased relative growth of the lower anterior face. Conversely, normodivergent and hypodivergent groups exhibit stable positioning of the maxilla relative to the anterior cranial base, with the forward rotation of the mandible. Furthermore, the hyperdivergent maxilla and mandible become relatively shorter and posteriorly positioned with age compared with the other groups. CONCLUSIONS: This study demonstrates how hyperdivergent growth, particularly restricted growth and positioning of the maxilla, results in a higher potential risk for Class II malocclusion. Future work will investigate growth patterns within each classification of facial divergence.

Bayesian approach to longitudinal craniofacial growth: The Craniofacial Growth Consortium Study.

Early in the 20th century, a series of studies were initiated across North America to investigate and characterize childhood growth. The Craniofacial Growth Consortium Study (CGCS) combines craniofacial records from six of those growth studies (15,407 lateral cephalograms from 1,913 individuals; 956 females, 957 males, primarily European descent). Standard cephalometric points collected from the six studies in the CGCS allows direct comparison of craniofacial growth patterns across six North American locations. Three assessors collected all cephalometric points and the coordinates were averaged for each point. Twelve measures were calculated from the averaged coordinates. We implemented a multilevel double logistic equation to estimate growth trajectories fitting each trait separately by sex. Using Bayesian inference, we fit three models for each trait with different random effects structures to compare differences in growth patterns among studies. The models successfully identified important growth milestones (e.g., age at peak growth velocity, age at cessation of growth) for most traits. In a small number of cases, these milestones could not be determined due to truncated age ranges for some studies and slow, steady growth in some measurements. Results demonstrate great similarity among the six growth studies regarding craniofacial growth milestone estimates and the overall shape of the growth curve. These similarities suggest minor variation among studies resulting from differences in protocol, sample, or possible geographic variation. The analyses presented support combining the studies into the CGCS without substantial concerns of bias. The CGCS, therefore, provides an unparalleled opportunity to examine craniofacial growth from childhood into adulthood.

Mandibular symphyseal fusion in fossil primates: Insights from correlated patterns of jaw shape and masticatory function in living primates.

OBJECTIVES: Variation in primate masticatory form and function has been extensively researched through both morphological and experimental studies. As a result, symphyseal fusion in different primate clades has been linked to either the recruitment of vertically directed balancing-side muscle force, the timing and recruitment of transversely directed forces, or both. This study investigates the relationship between jaw muscle activity patterns and morphology in extant primates to make inferences about masticatory function in extinct primates, with implications for understanding the evolution of symphyseal fusion. MATERIALS AND METHODS: Three-dimensional mandibular landmark data were collected for 31 extant primates and nine fossil anthropoids and subfossil lemur species. Published electromyography (EMG) data were available for nine of the extant primate species. Partial least squares analysis and phylogenetic partial least squares analysis were used to identify relationships between EMG and jaw shape data and evaluate variation in jaw morphology. RESULTS: Primates with partial and complete symphyseal fusion exhibit shape-function patterns associated with the wishboning motor pattern and loading regime, in contrast to shape-function patterns of primates with unfused jaws. All fossil primates examined (except Apidium) exhibit jaw morphologies suggestive of the wishboning motor pattern demonstrated in living anthropoids and indriids. DISCUSSION: Partial fusion in Catopithecus, similar to indriids and some subfossil lemurs, may be sufficient to resist, or transfer, some amounts of transversely directed balancing-side muscle force at the symphysis, representing a transition to greater reliance on transverse jaw movement during mastication. Furthermore, possible functional convergences in physiological patterns during chewing (i.e., Archaeolemur) are identified.

Clinical implications of age-related change of the mandibular plane angle.

OBJECTIVE: To identify trajectories of ontogenetic change in the mandibular plane angle (MPA) and to describe the influence of sex and other factors on MPA during growth. SETTING/SAMPLE: The data consisted of 7026 MPA measurements from lateral cephalographs representing longitudinal series from ages 6 to 21 for 728 individuals from the Craniofacial Growth Consortium Study (CGCS). MATERIALS AND METHODS: Facial type was determined from MPA for each assessment, with the assessment closest to age 18 representing the adult facial type. The sample includes 366 males and 362 females, each with between 2 and 15 cephalographs. The mean number of cephalographs per individual is 10. Variation in childhood MPA (earliest assessment between 6 and 9 years of age) and adult MPA (closest assessment to age 18 between 15 and 21 years of age), and change in MPA from childhood to adulthood were compared by sex and adult facial type using ANOVA and post hoc t tests. RESULTS: Mandibular plane angle decreased from childhood to adulthood in 92% of males and 81% of females, yet increased in 36% of males and 50% of females with the hyper-divergent adult facial type. Childhood MPA and overall change in MPA were significantly different by adult facial type. CONCLUSIONS: Adult facial type is associated with differences in childhood MPA and change in MPA during growth. There are multiple ontogenetic pathways by which an individual can achieve a normo-divergent adult facial type, and an individual's childhood MPA does not necessarily correspond to his or her adult facial type.

Hominoid intraspecific cranial variation mirrors neutral genetic diversity.

Natural selection, developmental constraint, and plasticity have all been invoked as explanations for intraspecific cranial variation in humans and apes. However, global patterns of human cranial variation are congruent with patterns of genetic variation, demonstrating that population history has influenced cranial variation in humans. Here we show that this finding is not unique to Homo sapiens but is also broadly evident across extant ape species. Specifically, taxa that exhibit greater intraspecific cranial shape variation also exhibit greater genetic diversity at neutral autosomal loci. Thus, cranial shape variation within hominoid taxa reflects the population history of each species. Our results suggest that neutral evolutionary processes such as mutation, gene flow, and genetic drift have played an important role in generating cranial variation within species. These findings are consistent with previous work on human cranial morphology and improve our understanding of the evolutionary processes that generate intraspecific cranial shape diversity within hominoids. This work has implications for the analysis of selective and developmental pressures on the cranium and for interpreting shape variation in fossil hominin crania.

Evaluating the potential for tactical hunting in the Middle Stone Age: Insights from a bonebed of the extinct bovid, Rusingoryx atopocranion.

The foraging behaviors of Middle Stone Age (MSA) early modern humans have largely been based on evidence from well-stratified cave sites in South Africa. Whereas these sites have provided an abundance of data for behavioral reconstruction that are unmatched elsewhere in Africa, they are unlikely to preserve evidence of the diversity of foraging strategies employed by MSA hunters who lived in a variety of ecological and landscape settings across the African continent. Here we describe the results of recent excavations at the open-air site of Bovid Hill at Wakondo, Rusinga Island, Kenya, which yielded 24 in situ MSA artifacts within an assemblage of bones comprised exclusively of the extinct alcelaphin bovid Rusingoryx atopocranion. The excavated faunal assemblage is characterized by a prime-age-dominated mortality profile and includes cut-marked specimens and an associated MSA Levallois blade-based artifact industry recovered from a channel deposit dated to 68 ± 5 ka by optically stimulated luminescence. Taphonomic, geologic, and faunal evidence points to mass exploitation of Rusingoryx by humans at Bovid Hill, which likely represents an initial processing site that was altered post-depositionally by fluvial processes. This site highlights the importance of rivers and streams for mass procurement in an open and seasonal landscape, and provides important new insights into MSA behavioral variability with respect to environmental conditions, site function, and tactical foraging strategies in eastern Africa. Bovid Hill thus joins a growing number of MSA and Middle Paleolithic localities that are suggestive of tactical hunting behaviors and mass capture of gregarious ungulate prey.

A detailed assessment of the maxillary morphology of Limnopithecus evansi with implications for the taxonomy of the genus.

Limnopithecus is a small-bodied catarrhine genus that is widespread throughout early Miocene sites in East Africa. Although two species of this genus have been described - Limnopithecus legetet (type species) and Limnopithecus evansi - they are poorly known anatomically and their systematic positions remain unresolved. Here, we provide detailed descriptions and comparisons for two well-preserved maxillary specimens that we attribute to L. evansi. These specimens come from the type locality of the species, Songhor in western Kenya, and add greatly to our knowledge of its dentognathic morphology. Together, they preserve the entire unilateral upper dentition, with overlapping elements demonstrating conspecificity, and provide new information about I(2) morphology and aspects of the palate, nasal aperture, and maxillary sinuses. Detailed morphological comparisons suggest that specimens referred to Limnopithecus from Songhor, Koru, and Rusinga share a unique I(2) morphology not found in any other early Miocene catarrhine. This argues in favor of congeneric status for L. evansi and L. legetet. Moreover, features such as a broad palate, premolar morphology, and the relative proportions of the premolars of L. evansi distinguish it from Lomorupithecus harrisoni, another early Miocene catarrhine from Napak, Uganda. This finding challenges a recently proposed taxonomic interpretation that Lomorupithecus and L. evansi are conspecific. Our results underscore the distinctiveness of L. evansi and Lo. harrisoni, thereby reaffirming the validity of the taxon Lo. harrisoni and indicating that the Songhor and Napak catarrhine communities were relatively distinct, despite their apparent contemporaneity.

Mechanical evidence that Australopithecus sediba was limited in its ability to eat hard foods.

Australopithecus sediba has been hypothesized to be a close relative of the genus Homo. Here we show that MH1, the type specimen of A. sediba, was not optimized to produce high molar bite force and appears to have been limited in its ability to consume foods that were mechanically challenging to eat. Dental microwear data have previously been interpreted as indicating that A. sediba consumed hard foods, so our findings illustrate that mechanical data are essential if one aims to reconstruct a relatively complete picture of feeding adaptations in extinct hominins. An implication of our study is that the key to understanding the origin of Homo lies in understanding how environmental changes disrupted gracile australopith niches. Resulting selection pressures led to changes in diet and dietary adaption that set the stage for the emergence of our genus.

A systematic revision of Proconsul with the description of a new genus of early Miocene hominoid.

For more than 80 years, Proconsul has held a pivotal position in interpretations of catarrhine evolution and hominoid diversification in East Africa. The majority of what we 'know' about Proconsul, however, derives from abundant younger fossils found at the Kisingiri localities on Rusinga and Mfangano Islands rather than from the smaller samples found at Koru--the locality of the type species, Proconsul africanus--and other Tinderet deposits. One outcome of this is seen in recent attempts to expand the genus "Ugandapithecus" (considered here a junior subjective synonym of Proconsul), wherein much of the Tinderet sample was referred to that genus based primarily on differentiating it from the Kisingiri specimens rather than from the type species, P. africanus. This and other recent taxonomic revisions to Proconsul prompted us to undertake a systematic review of dentognathic specimens attributed to this taxon. Results of our study underscore and extend the substantive distinction of Tinderet and Ugandan Proconsul (i.e., Proconsul sensu stricto) from the Kisingiri fossils, the latter recognized here as a new genus. Specimens of the new genus are readily distinguished from Proconsul sensu stricto by morphology preserved in the P. africanus holotype, but also in I(1)s, lower incisors, upper and lower canines, and especially mandibular characteristics. A number of these differences are more advanced among Kisingiri specimens in the direction of crown hominoids. Proconsul sensu stricto is characterized by a suite of unique features that strongly unite the included species as a clade. There have been decades of contentious debate over the phylogenetic placement of Proconsul (sensu lato), due in part to there being a mixture of primitive and more advanced morphology within the single genus. By recognizing two distinct clades that, in large part, segregate these character states, we believe that better phylogenetic resolution can be achieved.

Stable isotope paleoecology of Late Pleistocene Middle Stone Age humans from the Lake Victoria basin, Kenya.

Paleoanthropologists have long argued that environmental pressures played a key role in human evolution. However, our understanding of how these pressures mediated the behavioral and biological diversity of early modern humans and their migration patterns within and out of Africa is limited by a lack of archaeological evidence associated with detailed paleoenvironmental data. Here, we present the first stable isotopic data from paleosols and fauna associated with Middle Stone Age (MSA) sites in East Africa. Late Pleistocene (∼100-45 ka, thousands of years ago) sediments on Rusinga and Mfangano Islands in eastern Lake Victoria (Kenya) preserve a taxonomically diverse, non-analog faunal community associated with MSA artifacts. We analyzed the stable carbon and oxygen isotope composition of paleosol carbonate and organic matter and fossil mammalian tooth enamel, including the first analyses for several extinct bovids such as Rusingoryx atopocranion, Damaliscus hypsodon, and an unnamed impala species. Both paleosol carbonate and organic matter data suggest that local habitats associated with human activities were primarily riverine woodland ecosystems. However, mammalian tooth enamel data indicate that most large-bodied mammals consumed a predominantly C4 diet, suggesting an extensive C4 grassland surrounding these riverine woodlands in the region at the time. These data are consistent with other lines of paleoenvironmental evidence that imply a substantially reduced Lake Victoria at this time, and demonstrate that C4 grasslands were significantly expanded into equatorial Africa compared with their present distribution, which could have facilitated dispersal of human populations and other biotic communities. Our results indicate that early populations of Homo sapiens from the Lake Victoria region exploited locally wooded and well-watered habitats within a larger grassland ecosystem.

Dental microwear profilometry of African non-cercopithecoid catarrhines of the Early Miocene.

The Early Miocene of Kenya has yielded the remains of many important stem catarrhine species that provide a glimpse of the East African primate radiation at a time of major faunal turnover. These taxa have been subject to innumerable studies, yet there is still no consensus on their dietary niches. Here we report results of an analysis of dental microwear textures of non-cercopithecoid catarrhines from the Early Miocene of Kenya. Scanning confocal profilometry of all available molar specimens with undamaged occlusal surfaces revealed 82 individuals with unobscured antemortem microwear, representing Dendropithecus, Micropithecus, Limnopithecus, Proconsul, and Rangwapithecus. Scale-sensitive fractal analysis was used to generate microwear texture attributes for each individual, and the fossil taxa were compared with each other using conservative non-parametric statistical tests. This study revealed no discernible variation in microwear texture among the fossil taxa, which is consistent with results from a previous feature-based microwear study using smaller samples. Our results suggest that, despite their morphological differences, these taxa likely often consumed foods with similar abrasive and fracture properties. However, statistical analyses of microwear texture data indicate differences between the Miocene fossil sample and several extant anthropoid primate genera. This suggests that the African non-cercopithecoid catarrhines included in our study, despite variations in tooth form, had generalist diets that were not yet specialized to the degree of many modern taxa.

Three-dimensional geometric morphometric analysis of talar morphology in extant gorilla taxa from highland and lowland habitats.

Western gorillas (Gorilla gorilla) are known to climb significantly more often than eastern gorillas (Gorilla beringei), a behavioral distinction attributable to major differences in their respective habitats (i.e., highland vs. lowland). Genetic evidence suggests that the lineages leading to these taxa began diverging from one another between approximately 1 and 3 million years ago. Thus, gorillas offer a special opportunity to examine the degree to which morphology of recently diverged taxa may be "fine-tuned" to differing ecological requirements. Using three-dimensional (3D) geometric morphometrics, we compared talar morphology in a sample of 87 specimens including western (lowland), mountain (highland), and grauer gorillas (lowland and highland populations). Talar shape was captured with a series of landmarks and semilandmarks superimposed by generalized Procrustes analysis. A between-group principal components analysis of overall talar shape separates gorillas by ecological habitat and by taxon. An analysis of only the trochlea and lateral malleolar facet identifies subtle variations in trochlear shape between western lowland and lowland grauer gorillas, potentially indicative of convergent evolution of arboreal adaptations in the talus. Lastly, talar shape scales differently with centroid size for highland and lowland gorillas, suggesting that ankle morphology may track body-size mediated variation in arboreal behaviors differently depending on ecological setting. Several of the observed shape differences are linked biomechanically to the facilitation of climbing in lowland gorillas and to stability and load-bearing on terrestrial substrates in the highland taxa, providing an important comparative model for studying morphological variation in groups known only from fossils (e.g., early hominins).

Morphometry, geometry, function, and the future.

The proliferation of geometric morphometrics (GM) in biological anthropology and more broadly throughout the biological sciences has resulted in a multitude of studies that adopt landmark-based approaches for addressing a variety of questions in evolutionary morphology. In some cases, particularly in the realm of systematics, the fit between research question and analytical design is quite good. Functional-adaptive studies, however, do not readily conform to the methods available in the GM toolkit. The symposium organized by Terhune and Cooke entitled "Assessing function via shape: What is the place of GM in functional morphology?" held at the 2013 meetings of the American Association of Physical Anthropologists was designed specifically to explore this relationship between landmark-based methods and analyses of functional morphology, and the articles in this special issue, which stem in large part from this symposium, provide numerous examples of how the two approaches can complement and contrast each other. Here, we underscore some of the major difficulties in interpreting GM results within a functional regime. In combination with other contributions in this issue, we identify emerging areas of research that will help bridge the gap between multivariate morphometry and functional-adaptive analysis. Ultimately, neither geometric nor functional morphometric approaches is sufficient to elaborate the adaptive pathways that explain morphological evolution through natural selection. These perspectives must be further integrated with research from physiology, developmental biology, genomics, and ecology.

Remnants of an ancient forest provide ecological context for Early Miocene fossil apes.

The lineage of apes and humans (Hominoidea) evolved and radiated across Afro-Arabia in the early Neogene during a time of global climatic changes and ongoing tectonic processes that formed the East African Rift. These changes probably created highly variable environments and introduced selective pressures influencing the diversification of early apes. However, interpreting the connection between environmental dynamics and adaptive evolution is hampered by difficulties in locating taxa within specific ecological contexts: time-averaged or reworked deposits may not faithfully represent individual palaeohabitats. Here we present multiproxy evidence from Early Miocene deposits on Rusinga Island, Kenya, which directly ties the early ape Proconsul to a widespread, dense, multistoried, closed-canopy tropical seasonal forest set in a warm and relatively wet, local climate. These results underscore the importance of forested environments in the evolution of early apes.