Interspecific perspective on mechanical and nonmechanical models of primate circumorbital morphology.

Linear dimensions and angular orientations of the browridge, postorbital bar, and postorbital septum were obtained from a representative series of primates and compared with variables associated with several nonmechanical and biomechanical/mechanical models put forward to explain the form and function of the circumorbital region. Analyses of the results indicate that face size is the primary determinant of variation in primate circumorbital morphology. Anteroposterior browridge thickness is correlated with neural-orbital disjunction among anthropoid primates, but not among prosimians. This difference appears related to differences in the construction of the upper face and anterior cranial fossa between prosimians and anthropoids. Little support is demonstrated for the anterior dental loading model of browridge development. Mediolateral postorbital bar width and (to a lesser degree) browridge height are correlated with neurofacial torsion during mastication and variation in masticatory muscle size. These analyses further suggest that since circumorbital structures (especially the browridges) are located the farthest away from the chewing apparatus, they are least affected by masticatory stresses.     

Ontogenetic study of the supraorbital region in modern humans: a longitudinal test of the spatial model

The structural significance of the hominid supraorbital torus and its morphological variation have always been a controversial topic in physical anthropology. Understanding the function of browridge variation in living and fossil human populations is relevant to questions of human evolution. This study utilizes radiograph images to evaluate the spatial model in modern humans during ontogeny. This structural model attributes variation in the supraorbital region to the positional relationship between the neurocranium and the orbits. The relationship between measurements of the antero-posterior supraorbital length and the factors specified in the spatial model were assessed by correlation and partial correlation analyses. Growth rates were also examined to study ontogenetic trajectories and infer aspects of developmental relationships between critical variables. Results agree with previous research supporting the existence of spatial influences between the neural and orbital-upper facial regions on browridge length during ontogeny.     

The mammalian postorbital bar as a torsion-resisting helical strut

The mammalian skull is asymmetrically loaded during mastication because most of these animals chew on only one side at a time. This loading regime tends to twist the braincase relative to the rostral, tooth bearing part of the skull at the zone of potential weakness between the orbits. This torsional effect is exaggerated, and a postorbital bar is present, in those animals with very large masseter and pterygoid muscles. The lines of action of these muscles are oriented at large angles to the long axis of the skull in lateral view, providing large components of force that twist the skull segments relative to one another. When the temporalis is the dominant muscle, the torsional effect is usually less important, and the bar is absent, because this muscle acts at a smaller angle to the skull axis. The postorbital bar exhibits the predicted three dimensional spatial orientation required to resist torsional forces: it is a segment of an imaginary 45° helix that is wound around the skull, if the skull is idealized as a cylinder. This orientation is significant because, in general, maximum compressive and tensile shear stresses lie along 45° helices on a cylinder loaded in torsion; to resist torsion, material should be placed far from the axis of torsion and along a helix oriented at 45° to the deforming forces. Each half of a supraorbital ridge is also a segment of a 45° helix that is perpendicular to the helix passing through the postorbital bar. This model suggests that the postorbital bar is loaded in compression on the chewing side and in tension on the non-chewing side; the supraorbital ridge is loaded in tension on the chewing side and in compression on the non-chewing side.     

Septa and processes: convergent evolution of the orbit in haplorhine primates and strigiform birds

According to the “nocturnal visual predation hypothesis” (NVPH), the convergent eyes and orbits of primates result from selection for improved stereoscopic depth perception to facilitate manual capture of prey at night. Within primates, haplorhines share additional derived orbital morphologies, including a postorbital septum and greater orbital convergence than any other mammalian clade. While the homology and function of the haplorhine septum remain controversial, experimental data suggest that septa evolved to inhibit mechanical disturbance of the orbital contents by the anterior temporalis muscle during mastication. According to this “insulation hypothesis,” haplorhines are particularly susceptible to disruption of the orbital contents because they have large and highly convergent eyes and orbits. However, comparative tests of the insulation hypothesis have been hindered by the morphological uniqueness of the haplorhine septum among mammals. Among birds, owls (Strigiformes) exhibit an expanded postorbital process that may be functionally analogous to the haplorhine septum. Here we present a comparative analysis of orbital morphology in 103 avian species that tests two hypotheses: (1) large, convergent orbits are associated with nocturnal visual predation, and (2) the strigiform postorbital process and haplorhine postorbital septum similarly function to insulate the eyes from contractions of mandibular adductors. Strigiforms, as nocturnal visual predators, possess relatively large orbits and exhibit the highest degree of orbital convergence in our sample. Notably, orbital convergence does not scale with orbit size in birds as in mammals. Owls are also unique among the birds examined in possessing extensive, plate-like postorbital processes that largely isolate the orbits from the temporal fossae. Furthermore, dissections of four owl species demonstrate that the expanded strigiform postorbital process deflects the path of mandibular adductors around the eye's inferolateral margin. These findings provide further comparative support for both the NVPH and the insulation hypothesis.     

Morphometric testing of structural hypotheses of the supraorbital region in modern humans

Our understanding of the functional morphology of the primate supraorbital region is based largely on previous morphometric and in vivo mechanical tests of hypotheses in non-human anthropoids. Prior tests of two structural hypotheses explaining morphological variation in the supraorbital region, the craniofacial size hypothesis and the spatial hypothesis, did not fully consider modern humans. We extend these previous findings to include modern humans by conducting morphometric tests of these two hypotheses in a sample of adult Melanesian crania. Morphometric correlates of structural predictions for the craniofacial size and spatial hypotheses were developed and compared to measurements of the supraorbital region via bivariate product-moment correlations. Measurements of the supraorbital region are significantly correlated with a craniofacial size estimate across individuals from this Melanesian sample. This result supports the prediction of the craniofacial size hypothesis that the magnitude of the supraorbital region is proportional to craniofacial size. The predicted link between the degree of neural-orbital disjunction and the magnitude of the supraorbital region, explicated in the spatial hypothesis, receives mixed support in the correlation analysis. These two results agree with previous research indicating that support for the craniofacial size and spatial hypotheses can be found across and within anthropoid primate species, including modern humans. Correlational support for both the craniofacial size and spatial hypotheses suggests multiple factors influence variation in the modern human supraorbital region. Thus, a single hypothesis cannot fully account for modern human variation in this region. The low bivariate correlation coefficients in this study further question whether existing hypotheses can adequately explain morphological variation in the supraorbital region in a primate population sample. Novel functional, structural, behavioral and developmental ideas must be explored if we are to better understand morphological variation in the modern human supraorbital region.     

Strain in the galago facial skull

Little experimental work has been directed at understanding the distribution of stresses along the facial skull during routine masticatory behaviors. Such information is important for understanding the functional significance of the mammalian circumorbital region. In this study, bone strain was recorded along the dorsal interorbit, postorbital bar, and mandibular corpus in Otolemur garnettii and O. crassicaudatus (greater galagos) during molar chewing and biting. We determined principal-strain magnitudes and directions, compared peak shear-strain magnitudes between various regions of the face, and compared galago strain patterns with similar experimental data for anthropoids. This suite of analyses were used to test the facial torsion model (Greaves [1985] J Zool (Lond) 207:125-136; [1991] Zool J Linn Soc 101:121-129; [1995] Functional morphology in vertebrate paleontology. Cambridge: Cambridge University Press, p 99-115). A comparison of galago circumorbital and mandibular peak strains during powerful mastication indicates that circumorbital strains are very low in magnitude. This demonstrates that, as in anthropoids, the strepsirhine circumorbital region is highly overbuilt for countering routine masticatory loads. The fact that circumorbital peak-strain magnitudes are uniformly low in both primate suborders undermines any model that emphasizes the importance of masticatory stresses as a determinant of circumorbital form, function, and evolution. Preliminary data also suggest that the difference between mandibular and circumorbital strains is greater in larger-bodied primates. This pattern is interpreted to mean that sufficient cortical bone must exist in the circumorbital region to prevent structural failure due to nonmasticatory traumatic forces. During unilateral mastication, the direction of epsilon(1) at the galago dorsal interorbit indicates the presence of facial torsion combined with bending in the frontal plane. Postorbital bar principal-strain directions during mastication are oriented, on average, very close to 45 degrees relative to the skull's long axis, much as predicted by the facial torsion model. When chewing shifts from one side of the face to the other, there is a characteristic reversal or flip-flop in principal-strain directions for both the interorbit and postorbital bar. Although anthropoids also exhibit an interorbital reversal pattern, peak-strain directions for this clade are opposite those for galagos. The presence of such variation may be due to suborder differences in relative balancing-side jaw-muscle force recruitment. Most importantly, although the strain-direction data for the galago circumorbital region offer support for the occurrence of facial torsion, the low magnitude of these strains suggests that this loading pattern may not be an important determinant of circumorbital morphology.     

Masticatory loading and bone adaptation in the supraorbital torus of developing macaques

Research on the evolution and adaptive significance of primate craniofacial morphologies has focused on adult, fully developed individuals. Here, we investigate the possible relationship between the local stress environment arising from masticatory loadings and the emergence of the supraorbital torus in the developing face of the crab‐eating macaque Macaca fascicularis. By using finite element analysis (FEA), we are able to evaluate the hypothesis that strain energy density (SED) magnitudes are high in subadult individuals with resulting bone growth in the supraorbital torus. We developed three micro‐CT‐based FEA models of M. fascicularis skulls ranging in dental age from deciduous to permanent dentitions and validated them against published experimental data. Applied masticatory muscle forces were estimated from physiological cross‐sectional areas of macaque cadaveric specimens. The models were sequentially constrained at each working side tooth to simulate the variation of the bite point applied during masticatory function. Custom FEA software was used to solve the voxel‐based models and SED and principal strains were computed. A physiological superposition SED map throughout the face was created by allocating to each element the maximum SED value from each of the load cases. SED values were found to be low in the supraorbital torus region throughout ontogeny, while they were consistently high in the zygomatic arch and infraorbital region. Thus, if the supraorbital torus arises to resist masticatory loads, it is either already adapted in each of our subadult models so that we do not observe high SED or a lower site‐specific bone deposition threshold must apply. Am J Phys Anthropol, 2009. © 2008 Wiley‐Liss, Inc.     

Browridge development in cercopithecidae: A test of two models

Theoretical discussions of primate browridge formation have resulted in several interpretations of its form and function. Lateral radiographs of adult Old World monkeys, representing most cercopithecine and colobine genera, were examined to address whether both biomechanical and spatial factors influence the development of a supraorbital torus. A linear measurement of browridge size was compared with a series of measures related to each model. Partial correlations were used to ascertain the relative independence of biomechanical (model I or II) and spatial effects upon torus formation. Allometric (size-related) shape changes were evaluated with log-linear bivariate regression analysis; subfamily differences in scaling patterns, with an analysis of covariance. When spatial and biomechanical (I or II) factors were both significantly related to brow size, additive and interactive multiple regression models were used to further assess the manner by which each set mutually affects variation in browridge dimensions. Correlation analyses were repeated with size-corrected antilogged residuals to eliminate a potentially spurious effect of skull size. Old World monkeys provide support of the spatial model. Also of interest is that skull size emerges as a primary influence on torus formation. Several alternative explanations are also put forward to account for browridge development in each subfamily.     

Masticatory stress, orbital orientation and the evolution of the primate postorbital bar

A postorbital bar is one of a suite of derived features which distinguishes basal primates from their putative sister taxon, plesiadapiforms. Two hypotheses have been put forward to explain postorbital bar development and variation in circumorbital form: the facial torsion model and visual predation hypothesis. To test the facial torsion model, we employ strain data on circumorbital and mandibular loading patterns in representative primates with a postorbital bar and masticatory apparatus similar to basal primates. To examine the visual predation hypothesis, we employ metric data on orbit orientation in Paleocene and Eocene primates, as well as several clades of visual predators and foragers that vary interspecifically in postorbital bar formation.A comparison of galago circumorbital and mandibular peak strains during powerful mastication demonstrates that circumorbital strains are quite low. This indicates that, as in anthropoids, the strepsirhine circumorbital region is excessively overbuilt for countering routine masticatory loads. The fact that circumorbital peak-strain levels are uniformly low in both primate suborders undermines any model which posits that masticatory stresses are determinants of circumorbital form, function and evolution. This is interpreted to mean that sufficient cortical bone must exist to prevent structural failure due to non-masticatory traumatic forces. Preliminary data also indicate that the difference between circumorbital and mandibular strains is greater in larger taxa.Comparative analyses of several extant analogs suggest that the postorbital bar apparently provides rigidity to the lateral orbital margins to ensure a high level of visual acuity during chewing and biting. The origin of the primate postorbital bar is linked to changes in orbital convergence and frontation at smaller sizes due to nocturnal visual predation and increased encephalization. By incorporating in vivo and fossil data, we reformulate the visual predation hypothesis of primate origins and thus offer new insights into major adaptive transformations in the primate skull.     

Spatial patterning of bone stiffness in the anterior mandibular corpus of Macaca fascicularis: Implications for models of bone adaptation

Elastic modulus of bone from the anterior mandibular corpus was determined via microindentation in a mixed-sex ontogenetic sample (N = 14) of Macaca fascicularis. This investigation focused on the hypothesis that material heterogeneity in the macaque mandibular symphysis—provided an accounting of age and sex variation—is explicable as a means to homogenize strains in this region. Experimental data and theoretical models of masticatory loading indicate that in the absence of material compensation, large strain gradients exist in the anterior mandibular corpus of macaques, particularly between lingual and labial cortical plates owing to the effects of lateral transverse bending. Microindentation data indicate that juvenile macaques possess less stiff bone than their subadult and adult counterparts; however, sex differences in elastic modulus are not apparent. Anisotropy variation is idiosyncratic; that is, there is not a common pattern of variation in stiffness sampled among orthogonal planes across individuals. Similarly, differences in stiffness between lingual and labial cortical plates, as well as differences among alveolar, midcorpus, and basal regions are inconsistently observed. Consequently, we find little evidence in support of the hypothesis that spatial variation in bone stiffness functions to homogenize strains in the anterior corpus; in fact, in some individuals, this spatial variation serves to exacerbate, rather than to minimize, strain gradients. The mechanical benefit of elastic modulus variation in the macaque mandibular symphysis is unclear; this variation may not confer adaptive benefit in terms of structural integrity despite the fact that such variation has discernible functional consequences. Am J Phys Anthropol 156:649–660, 2015. © 2014 Wiley Periodicals, Inc.     

Primary homologies of the circumorbital bones of snakes

Some snakes have two circumorbital ossifications that in the current literature are usually referred to as the postorbital and supraorbital. We review the arguments that have been proposed to justify this interpretation and provide counter‐arguments that reject those conjectures of primary homology based on the observation of 32 species of lizards and 81 species of snakes (both extant and fossil). We present similarity arguments, both topological and structural, for reinterpretation of the primary homologies of the dorsal and posterior orbital ossifications of snakes. Applying the test of similarity, we conclude that the posterior orbital ossification of snakes is topologically consistent as the homolog of the lacertilian jugal, and that the dorsal orbital ossification present in some snakes (e.g., pythons, Loxocemus, and Calabaria) is the homolog of the lacertilian postfrontal. We therefore propose that the terms postorbital and supraorbital should be abandoned as reference language for the circumorbital bones of snakes, and be replaced with the terms jugal and postfrontal, respectively. The primary homology claim for the snake “postorbital” fails the test of similarity, while the term “supraorbital” is an unnecessary and inaccurate application of the concept of a neomorphic ossification, for an element that passes the test of similarity as a postfrontal. This reinterpretation of the circumorbital bones of snakes is bound to have important repercussions for future phylogenetic analyses and consequently for our understanding of the origin and evolution of snakes. J. Morphol. 274:973–986, 2013. © 2013 Wiley Periodicals, Inc.     

Skull ontogeny in Arrhinoceratops brachyops (Ornithischia: Ceratopsidae) and other horned dinosaurs

Disentangling ontogenetic from interspecific variation is key to understanding biodiversity in the fossil record, yet information on growth in the ceratopsid subfamily Chasmosaurinae is sparse. Here, we describe the partial skull of a juvenile chasmosaurine, attributed to Arrhinoceratops brachyops, within the context of more mature specimens of this species, to better understand the ontogenetic transformations therein. We show that as A. brachyops matured, the postorbital horncores became longer and shifted from a posterior to an anterior inclination, the delta‐shaped frill epiossifications became lower and fused to the underlying frill, and the face became more elongate. In these respects, A. brachyops closely resembled Triceratops, suggesting that these ontogenetic changes may have been common to all long‐horned chasmosaurines. However, an event‐paired cladistic analysis of Chasmosaurinae using a standardized matrix of 24 developmental characters reveals that the relative timing of ontogenetic events in Arrhinoceratops was more like that of Chasmosaurus, particularly in the relatively late reduction in scalloping around the frill margins. Thus, the ontogenetic similarities between Arrhinoceratops and Triceratops appear to be plesiomorphic, partly related to the retention of the elongate postorbital horncores, which are primitive for Ceratopsidae. This study elucidates the otherwise contentious evolutionary relationships of Arrhinoceratops, and highlights the importance of ontogenetic data for resolving phylogenies when morphological data from adults alone are inadequate. © 2015 The Linnean Society of London     

Morphological relationship between the cranial and supraorbital regions in Homo sapiens

Although some hypotheses that attempt to explain the variation in supraorbital region morphology in modern humans have been proposed, this issue is still not well understood. In this study, the craniofacial size and spatial models were tested using a sample of modern human crania from geographically diverse populations, and the co‐occurrence of the degrees of glabella (GL) and superciliary arch (ST) expression were analyzed. The two supraorbital structures were examined by visual assessment, and eight quantitative variables were included in the three‐way ANOVA, canonical variates analysis and partial rank correlation. The influences of sex and the region of origin of the cranial samples on the relationships between the examined variables and the degrees of supraorbital structures expression were also considered. The results only partially supported the craniofacial size and spatial models and suggested that GL and ST experienced separate influences during development. In the sample of all crania, the neurocranial size more strongly influenced the morphological variation of the ST than of the GL, and sex influenced both of these structures the most. The results suggest that sex may be the main factor (having an influence independent of the other traits) on the morphological variation of the GL and ST. Am J Phys Anthropol 156:110–124, 2015 © 2014 Wiley Periodicals, Inc.     

Homology between the recessus lateralis and cephalic sensory canals, with the proposition of additional synapomorphies for the Clupeiformes and the Clupeoidei

The recessus lateralis , a complex structure in the otic region of the skull that is probably associated with detection and analysis of small vibrational pressures and displacements, is widely recognized as a synapomorphy of the Clupeiformes. The Clupeiformes includes the Denticipitoidei, with one living species, Denticeps clupeoides , and the Clupeoidei, with about 360 living species commonly known as herrings and anchovies. Comparisons between details of the recessus lateralis of the Clupeoidei and Denticipitoidei, and the sensory cephalic canals of other teleosts, lead to hypotheses of a series of transformations of the cephalic sensory canals . Treating that complex as a single binary 'presence vs. absence' character as was traditional practice obscures important phylogenetically informative variation. Specific synapomorphies in that system exist for the Clupeiformes and the Clupeoidei. Hypothesized synapomorphies in the recessus lateralis for the Clupeiformes are the presence of a dilated internal temporal sensory canal in the pterotic, a postorbital branch of the supraorbital sensory canal located in a bony groove in the lateral wing of the frontal, and the terminal portions of preopercular and infraorbital sensory canals closely positioned. Hypothesized synapomorphies for the Clupeoidei are the presence of a postorbital branch of the supraorbital sensory canal located deep within the body of the lateral wing of the frontal, with the distal portion of that branch totally internal on the cranium, and the expanded distal portion of the postorbital branch of the supraorbital sensory canal. The homology of the sinus temporalis of Clupeoidei, and of the dermosphenotic of both Denticeps and the Clupeoidei, with those of other teleosts is also considered.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 141 , 257–270.     

Allometry and developmental integration of body growth in a piranha,Pygocentrus nattereri (Teleostei: Ostariophysi)

Piranhas, like many teleosts, change their diets on both ontogenetic and phylogenetic time scales. Prior studies have suggested that pervasive morphological changes in body form on a phylogenetic time scale may be related to changes in diet, but previous reports have found little shape change in piranhas on an ontogenetic time scale. We re-examine the post-transformational allometry of body form in one piranha, Pygocentrus nattereri (Kner), using the method of thin-plate splines decomposed by their partial warps. We find substantial evidence of allometry, primarily elongation of the mid-body relative to the more anterior and posterior regions, elongation of the postorbital and nape regions relative to the more anterior head and posterior body, and deepening of the head relative to the body. In addition to these pervasive changes throughout the body, there are some that are more localized, especially elongation of the postorbital region relative to eye diameter and snout, and an even more localized elongation of the snout relative to eye diameter. Initial dietary transitions are associated with changes in head and jaw proportions, but rates of shape change decelerate through growth, so that the final transition to a diet increasingly dominated by small whole fish appears associated with change largely in overall body size. © 1995 Wiley-Liss, Inc.     

The postorbital palatoquadrate articulation in elasmobranchs

Although modern hexanchiforms are the only extant elasmobranchs with a postorbital articulation, according to most morphological and molecular cladistic analyses they are not basal, suggesting that Huxley ( 1876 Proc Zool Soc 1876;24–59) correctly identified this articulation as “an altogether secondary connection.” A postorbital articulation is present in many Paleozoic sharks, but differs from that found in hexanchiforms in its morphology, topographic position on the braincase, and inferred ontogenetic origins. Furthermore, a postorbital articulation is absent in hybodonts (the putative extinct sister group to neoselachians). It is proposed that the term amphistylic should be restricted to the modern hexanchiform condition, where the articular facet is located on the primary postorbital process. An identical articulation probably existed in some extinct galeomorphs (e.g., ?Synechodus dubrisiensis, ?Paraorthacodus), but is not widespread within elasmobranchs generally. The term archaeostylic (“ancient pillar”) is proposed here for the suspensorial arrangement in Paleozic sharks with a postorbital articulation on the ventrolateral part of the lateral commissure. Such an articulation is not known in other gnathostomes and may represent a basal chondrichthyan synapomophy (especially if ?Pucapampella is a stem chondrichthyan), suggesting that the autodiastylic pattern is not primitive for chondrichthyans and that holocephalans have secondarily lost a postorbital articulation. The amphistylic condition may have arisen from the archaeostylic, or it could have been acquired independently within neoselachians, but in either case it is most parsimoniously viewed as apomorphic. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Craniofacial ontogeny in centrosaurine dinosaurs (Ornithischia: Geratopsidae): taxonomic and behavioral implications

Centrosaurine ceratopsians are characterized by well developed nasal horncores or bosses, relatively abbreviated supraorbital horncores or bosses, and adorned parietosquamosal frills. Recent study of several paucispecific (low diversity) bonebed assemblages in Alberta and Montana has contributed greatly to our understanding of ontogenetic and taxonomic variation in the skulls of centrosaurines. Relative age determination of centrosaurines is now possible through examination of ontogenetic change in several characters, including the surface bone morphology of specific skeletal elements. The within-group taxonomy of centrosaurines is based almost entirely on characters of the skull roof, relating particularly to horns and frills. Juvenile and sub-adult centrosaurines are characterized by relatively simple, unadorned skulls compared to their adult counterparts. As in numerous living taxa, the cranial ornaments of centrosaurines developed late in ontogeny, as individuals approached or attained adult size. An important implication arising directly from this study is that juvenile and sub-adult centrosaurines are difficult to distinguish taxonomically at the specific level. Two monospecific genera represented only by immature materials, Brachyceratops montanensis and Monoclonius crassus , cannot be defended and should be considered nomina dubia . The late ontogenetic development and diverse taxonomic variation of horn and frill morphologies support the contention diat these structures are best interpreted as reproductive characters employed in mate competition.     

Muscular and osseous anatomy of the primate anterior temporal fossa and the functions of the postorbital septum

Many adaptive explanations for anthropoid origins incorporate hypotheses regarding the function of the postorbital septum. Two hypotheses are evaluated here: Cachel's ([1979b] Am. J. Phys. Anthropol. 50:1–18) hypothesis that the anthropoid postorbital septum evolved to augment muscle attachment area in the anterior temporal fossa and Cartmill's ([1980] in RL Ciochon and AB Chiarelli (eds.): Evolutionary Biology of the New World Monkeys and Continental Drift. New York: Plenum, pp. 243–274.) hypothesis that the septum evolved to insulate the foveate eye of haplorhines from movements in the temporal fossa during mastication. Dissections of the masticatory muscles of 55 species of primates, with emphasis on the anatomy of the anterior temporal fossa, reveal that in all anthropoids the temporal muscles take origin from the portion of the septum formed by the frontal bone. In some platyrrhines this muscle is anterior temporalis, and in others it is zygomatico-mandibularis. In tarsiers and most platyrrhines, muscle attachment to the zygomatic portion of the postorbital septum is very restricted (and of possibly varying homologies), whereas in catarrhines the zygomatico-mandibularis arises from the postorbital ridge on the zygomatic portion of the septum. This suggests that, contrary to Cachel's hypothesis, the earliest anthropoids did not have extensive areas of muscle attachment on the postorbital septum, a suggestion supported by the bony morphology of Catopithecus browni. Dissections also indicate that in all haplorhines the anteriormost temporal fibers curve around the postorbital septum between origin and insertion, implying that, were the septum not present, the anterior temporal muscles would disturb the orbital contents when contracting. This suggests that insulation may have been the septum's original function, even in the absence of a retinal fovea. In anthropoids, the rostral migration of the line of action of the anterior temporal muscles relative to the eye is attributed to their possession of extreme degrees of both orbital frontation and convergence; in tarsiers it is attributed to their possession of both massively hypertrophied eyes and moderately convergent and frontated orbits. It is argued that the postorbital septum is most likely to have evolved in a morphological context similar to that exhibited by omomyids. © 1995 Wiley-Liss, Inc.     

Morphological affinities of the Sal'a 1 frontal bone

The human frontal bone from Sal'a, Slovak Republic, has previously entered into discussions of the morphological patterns of Central European Neandertals and the origins of early modern humans in that region. A morphological reassessment of its supraorbital region and a morphometric analysis of its overall proportions indicate that it falls well within expected ranges of variation of Late Pleistocene Neandertals and is separate from European earlier Upper Paleolithic early modern human crania. It is similar to the Qafzeh-Skhul sample in some metrical and supraorbital robusticity measures, but it contrasts with them in mid-sagittal curvature and supraorbital torus morphology. In the context of its probable oxygen isotope stage 5 age based on inferred biostratigraphic associations, it should not be employed directly for arguments relating to the emergence of modern humans in Central Europe.     

Morphological affinities of the al’a 1 frontal bone

The human frontal bone from al’a, Slovak Republic, has previously entered into discussions of the morphological patterns of Central European Neandertals and the origins of early modern humans in that region. A morphological reassessment of its supraorbital region and a morphometric analysis of its overall proportions indicate that it falls well within expected ranges of variation of Late Pleistocene Neandertals and is separate from European earlier Upper Paleolithic early modern human crania. It is similar to the Qafzeh-Skhul sample in some metrical and supraorbital robusticity measures, but it contrasts with them in mid-sagittal curvature and supraorbital torus morphology. In the context of its probable oxygen isotope stage 5 age based on inferred biostratigraphic associations, it should not be employed directly for arguments relating to the emergence of modern humans in Central Europe.