Computer simulations show that Neanderthal facial morphology represents adaptation to cold and high energy demands, but not heavy biting.

Three adaptive hypotheses have been forwarded to explain the distinctive Neanderthal face: (i) an improved ability to accommodate high anterior bite forces, (ii) more effective conditioning of cold and/or dry air and, (iii) adaptation to facilitate greater ventilatory demands. We test these hypotheses using three-dimensional models of Neanderthals, modern humans, and a close outgroup (Homo heidelbergensis), applying finite-element analysis (FEA) and computational fluid dynamics (CFD). This is the most comprehensive application of either approach applied to date and the first to include both. FEA reveals few differences between H. heidelbergensis, modern humans, and Neanderthals in their capacities to sustain high anterior tooth loadings. CFD shows that the nasal cavities of Neanderthals and especially modern humans condition air more efficiently than does that of H. heidelbergensis, suggesting that both evolved to better withstand cold and/or dry climates than less derived Homo We further find that Neanderthals could move considerably more air through the nasal pathway than could H. heidelbergensis or modern humans, consistent with the propositions that, relative to our outgroup Homo, Neanderthal facial morphology evolved to reflect improved capacities to better condition cold, dry air, and, to move greater air volumes in response to higher energetic requirements.

Mesopithecus pentelicus from the Turolian locality of Kryopigi (Kassandra, Chalkidiki, Greece).

New material of the Mio-Pliocene colobine Mesopithecus from the Turolian locality of Kryopigi (Greece) is described here. It includes a complete skull with the atlas attached and other dental and postcranial elements representing at least five individuals (four males and one female). The material is compared with Mesopithecus delsoni, Mesopithecus pentelicus, Mesopithecus monspessulanus and intermediate forms from more than a dozen Turolian localities of the Greco-Iranian province. These comparisons support the attribution of the Kryopigi material to M. pentelicus. The chronostratigraphic distribution of Mesopithecus species and intermediate forms suggests that the Kryopigi fauna could be dated as younger than the Perivolaki locality with M. delsoni/pentelicus (7.1-7.3 Ma, MN12) and older than the Dytiko localities with M. aff. pentelicus, M. cf. pentelicus and M. cf. monspessulanus (?middle MN13). The dimensions of the atlas are within the distribution of extant colobines. The skull shows bite-marks, probably caused by the hyaena Adcrocuta eximia.

Relationship between foramen magnum position and locomotion in extant and extinct hominoids.

From the Miocene Sahelanthropus tchadensis to Pleistocene Homo sapiens, hominins are characterized by a derived anterior position of the foramen magnum relative to basicranial structures. It has been previously suggested that the anterior position of the foramen magnum in hominins is related to bipedal locomotor behavior. Yet, the functional relationship between foramen magnum position and bipedal locomotion remains unclear. Recent studies, using ratios based on cranial linear measurements, have found a link between the anterior position of the foramen magnum and bipedalism in several mammalian clades: marsupials, rodents, and primates. In the present study, we compute these ratios in a sample including a more comprehensive dataset of extant hominoids and fossil hominins. First, we verify if the values of ratios can distinguish extant humans from apes. Then, we test whether extinct hominins can be distinguished from non-bipedal extant hominoids. Finally, we assess if the studied ratios are effective predictors of bipedal behavior by testing if they mainly relate to variation in foramen magnum position rather than changes in other cranial structures. Our results confirm that the ratios discriminate between extant bipeds and non-bipeds. However, the only ratio clearly discriminating between fossil hominins and other extant apes is that which only includes basicranial structures. We show that a large proportion of the interspecific variation in the other ratios relates to changes in facial, rather than basicranial, structures. In this context, we advocate the use of measurements based only on basicranial structures when assessing the relationship between foramen magnum position and bipedalism in future studies.

Semicircular Canal Size and Locomotion in Colobine Monkeys: A Cautionary Tale.

The semicircular canals of the inner ear constitute the organ of balance, tracking head rotation during movement and facilitating stabilisation of vision. Morphological characteristics of the canals are correlated with agility scores related to locomotion. To date, however, the relationship between canal morphology and specific locomotor behaviours, such as leaping, is unclear. Knowledge of such a relationship could strengthen the inferences of locomotion of extinct taxa. To test this, crania of two sets of closely related primate species (Presbytis melalophos and P. potenziani; Colobus guereza and C. polykomos) that differ in the percentage of leaping in their locomotor repertoire were examined using microscopic computed tomography. Three-dimensional virtual models of the bony labyrinth were derived, and the radius of curvature of each of the three canals was evaluated relative to cranial size. The findings are contradictory; one leaping form (P. melalophos) differs from its congener in possessing significantly larger lateral canals, a pattern seen in previous studies of primates, while the other leaper (C. guereza) has significantly smaller posterior canals than its close relative. These results undermine efforts to determine specific locomotor behaviours from the bony labyrinth of extinct primates.

Sinuses and flotation: does the aquatic ape theory hold water?

The idea that people went through an aquatic phase at some time in their evolutionary past is currently undergoing a popular resurgence (see Foley & Lahr). This idea has even started to gain some traction in more learned circles; the late paleoanthropologist Phillip Tobias wrote in support of aspects of it in an edited e-book and a conference on the topic held recently in London was endorsed by celebrities such as the television presenter Sir David Attenborough. Despite (or perhaps because of) the lack of interest within the academic community, advocates of the concept continue to fill the media (and blogosphere) with challenges to the "savannah hypothesis" of the origins of people and to bemoan the fact that their views are not taken seriously by mainstream academia.

Testing the reliability of the rearticulation of osteological primate pelves in comparative morphological studies.

The evolution of human pelvic form is primarily studied using disarticulated osteological material of living and fossil primates that need rearticulation to approximate anatomical position. To test whether this technique introduces errors that impact biological signals, virtual rearticulations of the pelvis in anatomical position from computed tomography scans were compared with rearticulated models from the same individuals for one female and one male of Homo sapiens, Pan troglodytes, Macaca mulatta, Lepilemur mustelinus, Galago senegalensis, and Nycticebus pygmaeus. "Cadaveric" pelvic bones were first analyzed in anatomical position, then the three bones were segmented individually, intentionally scattered, and "rearticulated" to test for rearticulation error. Three-dimensional landmarks and linear measurements were used to characterize the overall pelvis shape. Cadaveric and rearticulated pelves were not identical, but inter-specific and intra-specific shape differences were higher than the landmarking error in the cadaveric individuals and the landmarking/rearticulation error in the rearticulated pelves, demonstrating that the biological signal is stronger than the noise introduced by landmarking and rearticulation. The rearticulation process, however, underestimates the medio-lateral pelvic measurements in species with a substantial pubic gap (e.g., G. senegalensis, N. pygmaeus) possibly because the greater contribution of soft tissue to the pelvic girdle introduces higher uncertainty during rearticulation. Nevertheless, this discrepancy affects only the caudal-most part of the pelvis. This study demonstrates that the rearticulation of pelvic bones does not substantially affect the biological signal in comparative 3D morphological studies but suggests that anatomically connected pelves of species with wide pubic gaps should be preferentially included in these studies.

Frontal sinuses and human evolution.

The frontal sinuses are cavities inside the frontal bone located at the junction between the face and the cranial vault and close to the brain. Despite a long history of study, understanding of their origin and variation through evolution is limited. This work compares most hominin species' holotypes and other key individuals with extant hominids. It provides a unique and valuable perspective of the variation in sinuses position, shape, and dimensions based on a simple and reproducible methodology. We also observed a covariation between the size and shape of the sinuses and the underlying frontal lobes in hominin species from at least the appearance of Homo erectus. Our results additionally undermine hypotheses stating that hominin frontal sinuses were directly affected by biomechanical constraints resulting from either chewing or adaptation to climate. Last, we demonstrate their substantial potential for discussions of the evolutionary relationships between hominin species.

The Neanderthal face is not cold adapted.

Many morphological features of the Pleistocene fossil hominin Homo neanderthalensis, including the reputed large size of its paranasal sinuses, have been interpreted as adaptations to extreme cold, as some Neanderthals lived in Europe during glacial periods. This interpretation of sinus evolution rests on two assumptions: that increased craniofacial pneumatization is an adaptation to lower ambient temperatures, and that Neanderthals have relatively large sinuses. Analysis of humans, other primates, and rodents, however, suggests that the first assumption is suspect; at least the maxillary sinus undergoes a significant reduction in volume in extreme cold, in both wild and laboratory conditions. The second assumption, that Neanderthal sinuses are large, extensive, or even 'hyperpneumatized,' has held sway since the first specimen was described and has been interpreted as the causal explanation for some of the distinctive aspects of Neanderthal facial form, but has never been evaluated with respect to scaling. To test the latter assumption, previously published measurements from two-dimensional (2D) X-rays and new three-dimensional (3D) data from computed tomography (CT) of Neanderthals and temperate-climate European Homo sapiens are regressed against cranial size to determine the relative size of their sinuses. The 2D data reveal a degree of craniofacial pneumatization in Neanderthals that is both commensurate with the size of the cranium and comparable in scale with that seen in temperate climate H. sapiens. The 3D analysis of CT data from a smaller sample supports this conclusion. These results suggest that the distinctive Neanderthal face cannot be interpreted as a direct result of increased pneumatization, nor is it likely to be an adaptation to resist cold stress; an alternative explanation is thus required.

Long-term benzodiazepine and Z-drugs use in England: a survey of general practice [corrected].

BACKGROUND: Current British National Formulary (BNF) guidelines state that benzodiazepines and zolpidem, zopiclone, and zaleplon, commonly known as Z-drugs (BZD), be prescribed for no more than 4 weeks, although anecdotal data suggest that many patients are prescribed BZDs for much longer. As there are no recent, evidence-based estimates of long-term (>12 months) BZD use in the UK, the scale of this potential problem is unknown. AIM: To produce the first reliable, evidence-based estimate of long-term BZD use in the UK. DESIGN AND SETTING: Estimates of UK long-term BZD use were projected from data obtained from a survey conducted in 2014-2015 by the Bridge Project, a prescribed-drug withdrawal support charity in the North of England (Bradford). METHOD: Percentages of long-term users of BZD were derived from the survey, by sampling primary care GP surgeries with around 100 000 registered patients, and these were applied to UK-wide NHS patient numbers. The data were filtered to exclude the very young and old, and those with other health issues. RESULTS: The mean percentage of registered patients prescribed BZDs for more than a year in the survey sample is 0.69% (95% confidence interval [CI] = 0.54 to 0.84). Applying this value to national patient numbers yields a mean projection of 296 929 (95% CI = 232 553 to 361 305) long-term users of BZD in the UK. The data also suggest that as many as 119 165 of these patients may be willing to accept prescribed drug dependency withdrawal services. CONCLUSION: More than a quarter of a million people in the UK are likely to be taking highly dependency-forming hypnotic medication far beyond the recommended time scales. As there is evidence that long-term use of BZDs causes adverse physiological and neurological effects, and protracted withdrawal (with associated complications), this represents a serious public health problem.

Developmental response to cold stress in cranial morphology of Rattus: implications for the interpretation of climatic adaptation in fossil hominins.

Adaptation to climate occupies a central position in biological anthropology. The demonstrable relationship between temperature and morphology in extant primates (including humans) forms the basis of the interpretation of the Pleistocene hominin Homo neanderthalensis as a cold-adapted species. There are contradictory signals, however, in the pattern of primate craniofacial changes associated with climatic conditions. To determine the direction and extent of craniofacial change associated with temperature, and to understand the proximate mechanisms underlying cold adaptations in vertebrates in general, dry crania from previous experiments on cold- and warm-reared rats were investigated using computed tomography scanning and three-dimensional digitization of cranial landmarks. Aspects of internal and external cranial morphology were compared using standard statistical and geometric morphometric techniques. The results suggest that the developmental response to cold stress produces subtle but significant changes in facial shape, and a relative decrease in the volume of the maxillary sinuses (and nasal cavity), both of which are independent of the size of the skull or postcranium. These changes are consistent with comparative studies of temperate climate primates, but contradict previous interpretations of cranial morphology of Pleistocene Hominini.

The Logical Basis for the use of Continuous Characters in Phylogenetic Systematics.

It has been argued that continuous characteristics should be excluded from cladistic analysis for two reasons: because the data are considered inappropriate; and because the methods for the conversion of these data into codes are considered arbitrary. Metric data, however, fulfill the sole criterion for inclusion in phylogenetic analysis, the presence of homologous character states, and thus cannot be excluded as a class of data. The second line of reasoning, that coding methods are arbitrary, applies to gap and segment coding, but quantitative data can be coded in a nonarbitrary manner by means of tests of statistical significance. These procedures, which are both objective and repeatable, determine the probability that two taxa possess an homologous character state; that is, if they have inherited a particular central tendency and distribution of individual variates unchanged from a common ancestor. Thus, the application of statistical tests to quantitative data empirically detects the presence of evolu tionary change, the raw material of phylogenetic reconstruction.

The term "lateral recess" and craniofacial pneumatization in old world monkeys (Mammalia, Primates, Cercopithecoidea).

The primate superfamily Cercopithecoidea (or Old World monkeys) is characterized by a widespread lack of the maxillary sinus, a paranasal pneumatic space found in most other eutherian mammals. Previous discussions of the distribution of pneumatization in the group, however, have been ambiguous and contradictory, and have been further complicated by discussion of a poorly defined structure named the "lateral recess," linked implicitly to the maxillary sinus. Computed tomography (CT) was applied to dry crania of all cercopithecoid genera to evaluate the morphological relevance of the term "lateral recess." Results suggest that the "lateral recess" is a structural consequence of changes in skull form unrelated to pneumatization. Thus, the term should be abandoned. All Old World monkeys (except the genus Macaca) are found to lack the maxillary sinus, but a previously undescribed bulla, only separated from the nasal cavity anteriorly, was discovered in the Chinese golden monkey Rhinopithecus. If this bulla is related to the paranasal sinuses, it suggests that the initial change in cercopithecoid cranial evolution was a suppression of pneumatic development, which may have been subsequently reversed twice in the history of the group, in Macaca and Rhinopithecus.

Miocene hominoid craniofacial morphology and the emergence of great apes.

The initial cladogenic event between Hominoidea (apes, including humans) and Cercopithecoidea (Old World monkeys) consisted primarily of changes in the craniofacial region. These changes, seen in taxa commonly known as victoriapithecids and proconsulids, arose in a mosaic fashion. The divergence in the postcranium was more subtle; there are strong suggestions that apes initially adopted a tail-less pronograde arboreal quadrupedalism, while cercopithecoids became better adapted to a more terrestrial lifestyle. Recent phylogenetic analysis suggests that gibbons (Hylobates) have reversed derived craniofacial characters autapomorphically, contradicting the interpretation that the origin of apes sensu stricto coincides with the emergence of suspensory adaptations. The suspensory postcranium evolved later and appeared first in Eurasia; recent palaeobiogeographic reconstructions suggest that suspensory apes subsequently re-colonized Africa, as suggested nearly thirty years ago on neontological grounds. To test whether these two models of hominoid evolution are compatible, catarrhine craniofacial and postcranial traits, including those from Eurasian fossils, were subjected to parsimony analysis. The results demonstrate a mosaic pattern of derived characters, with gibbons reversing some traits of the face, which suggests their derivation from a 'great ape' face. Combined with the palaeobiogeography, a much longer, step-wise transition from primitive catarrhines to extant great apes than previously envisioned is supported. The pattern of craniofacial change is difficult to interpret in functional/adaptational terms, but the origin of brachiation may have arisen through character displacement due to competition with the emerging modern Old World monkey radiation in Eurasia.

Paranasal pneumatization in extant and fossil Cercopithecoidea.

Unlike most primates, extant cercopithecoids lack maxillary sinuses, which are pneumatic spaces in the facial skeleton lateral of the nasal cavity proper. Character state analysis of living cercopithecoids across well-supported topologies suggests that the sinus was lost at the origin of the superfamily, only to have evolved again convergently in extant macaques. Recent work has shown that a) the 'early loss' hypothesis is supported by the lack of any pneumatization in Victoriapithecus, a stem cercopithecoid, b) like extant macaques, the fossil cercopithecine Paradolichopithecus shows evidence of presence of the maxillary sinus (MS), and c) unlike extant colobines, the fossil colobine Libypithecus also possesses a maxillary sinus. To more fully assess the pattern of cercopithecoid sinus evolution, fossil taxa from both subfamilies (Colobinae, Cercopithecinae) were examined both visually and by computed tomography (CT). The observations were evaluated according to standard anatomical criteria for defining sinus spaces, and compared with data from all extant Old World monkey genera. Most taxa examined conformed to the pattern already discerned from extant cercopithecoids. Maxillary sinus absence in Theropithecus oswaldi, Mesopithecus, and Rhinocolobus is typical for all extant cercopithecids except Macaca. The fossil macaque Macaca majori possesses a well-developed maxillary sinus, as do all living species of the genus. Cercopithecoides, on the other hand, differs from all extant colobines in possessing a maxillary sinus. Thus, paranasal pneumatization has reemerged a minimum of two and possibly three times in cercopithecoids. The results suggest that maxillary sinus absence in cercopithecoids is due to suppression, rather than complete loss.

Independence of biomechanical forces and craniofacial pneumatization in Cebus.

Several different factors have been hypothesized as explanations of variation in primate paranasal sinus size. Biomechanical forces, particularly those associated with mastication, are frequently evoked to account for differences in primate craniofacial pneumatization. To test whether masticatory stresses are responsible for maxillary sinus volume diversity, two platyrrhine species of the genus Cebus (C. apella and C. albifrons) were examined. The former has been identified as a hard object feeder, and many morphological differences between the two species are attributable to differences in the mechanical properties of their respective diets. Sinus volumes were derived from serial coronal CT scans of the crania of adults. Several external cranial measurements were used to scale sinus volume relative to the size of the face. Relative measures of maxillary sinus volume were compared using standard statistical techniques. In all comparisons, the two capuchin species do not differ from one another significantly at P < 0.05. Thus, this "natural experiment" fails to support the interpretation that biomechanical forces acting on the facial skeleton substantially affect the degree of paranasal pneumatization in primates. This result suggests that it is unlikely that the maxillary sinus performs any function in relation to masticatory stress; other factors must be responsible for the variation in sinus volume among primates.

Presence of the maxillary sinus in fossil Colobinae (Cercopithecoides williamsi) from South Africa.

Extant cercopithecoid monkeys, except macaques, are distinguished among primates by their lack of paranasal pneumatization, including the maxillary sinus (MS). Analysis of this structure, widespread among Eutheria, suggests that its loss occurred in the cercopithecoid common ancestor; thus, the presence of the MS in macaques is not strictly homologous to that in other primates. CT analysis of the fossil species Victoriapithecus macinnesi supports this view, demonstrating the lack of the MS in this stem cercopithecoid. Recent evidence, however, has documented the presence of the MS in extinct cercopithecoids from the late Miocene and Pliocene. This study reports on CT examination of two fossil crania attributed to Cercopithecoides williamsi from South Africa, dated in the range, 3.0-1.5 Ma. BF 42a is a complete cranium from Bolts Farm; MP113 is an intact facial skeleton, including the anterior cranial vault, from the Makapansgat Limeworks. Both demonstrate MS presence, unknown in extant colobines and unexpected in most cercopithecoid monkeys. The relative size of the MS of BF 42a is similar to that of extant tropical and subtropical macaques. The presence of sinuses in several extinct colobines suggests that our understanding of the evolutionary history of these primates, and of the MS, is incomplete, and that other fossil cercopithecoids should be examined for this feature. The developmental plasticity exhibited in this feature, indicated by multiple loss and reemergence, provides further evidence that paranasal pneumatization has undergone a complex history of suppression and expression.

Clinal variation of maxillary sinus volume in Japanese macaques (Macaca fuscata).

Macaques (genus Macaca) are unique among cercopithecids in that they possess a maxillary sinus, and among anthropoids in that they demonstrate a relatively weak relationship between the size of this sinus and the cranium. To test the hypothesis that extrinsic factors may contribute to maxillary sinus size variation, a sample of 46 Japanese macaque (M. fuscata) crania from known localities were subjected to computed tomography (CT) imaging, and sinus volume and nasal cavity area were analyzed relative to latitude and temperature variables. The results suggest that the environmental factors are significant determinants of nasal cavity size in Japanese macaques, but that the relationships between the environment and maxillary sinus volume (MSV) are probably a passive consequence of changes in the size of the nasal cavity. The sinus shrinks as the nasal cavity expands, due to an increased need to condition inspired air in colder climates. This in turn suggests that the sinus itself does not contribute significantly to upper respiratory function.

Ancestral loss of the maxillary sinus in Old World monkeys and independent acquisition in Macaca.

Cercopithecoid monkeys are unique among primates in that all species (except macaques) lack a maxillary sinus, an unusual condition among eutherian mammals. Although this uncommon distribution of cranial pneumatization was noted previously, the phylogenetic ramifications have not been investigated fully. Recently, character state optimization analysis of computed tomography (CT) data from extant Old World monkeys suggested that the loss of the sinus may have occurred at the origin of the group, unlike previous hypotheses positing only a reduction in size of the structure. To critically evaluate the "early loss" hypothesis, a recently recovered complete cranium of Victoriapithecus macinnesi from Maboko Island, Kenya, was examined by CT to determine the extent of its cranial pneumatization. This taxon is crucial for evaluating character state evolution in Old World monkeys, due to its phylogenetic position, preceding the cercopithecine/colobine split. CT analysis reveals only cancellous bone lateral of the nasal cavity, indicating that Victoriapithecus does not possess a maxillary sinus. Phylogenetic evaluation of the fossil with extant catarrhine taxa strongly supports the early loss of the sinus in cercopithecoids. The results suggest that the maxillary sinus found in the genus Macaca is not homologous with that of other eutherians, which may provide insights into the origin and function (if any) of the paranasal pneumatizations.