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Matthew J. Ravosa - One of the best experts on this subject based on the ideXlab platform.
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Masticatory Loading, Function, and Plasticity: A Microanatomical Analysis of Mammalian Circumorbital Soft-Tissue Structures
Anatomical record (Hoboken N.J. : 2007), 2010Co-Authors: Eldin Jašarević, Jie Ning, Ashley N. Daniel, Rachel A. Menegaz, Jeffrey Johnson, M. Sharon Stack, Matthew J. RavosaAbstract:In contrast to experimental evidence regarding the Postorbital Bar, Postorbital septum, and browridge, there is exceedingly little evidence regarding the load-bearing nature of soft-tissue structures of the mammalian circumorbital region. This hinders our understanding of pronounced transformations during primate origins, in which euprimates evolved a Postorbital Bar from an ancestor with the primitive mammalian condition where only soft tissues spanned the lateral orbital margin between frontal bone and zygomatic arch. To address this significant gap, we investigated the Postorbital microanatomy of rabbits subjected to long-term variation in diet-induced masticatory stresses. Rabbits exhibit a masticatory complex and feeding behaviors similar to primates, yet retain a more primitive mammalian circumorbital region. Three cohorts were obtained as weanlings and raised on different diets until adult. Following euthanasia, Postorbital soft tissues were dissected away, fixed, and decalcified. These soft tissues were divided into inferior, intermediate, and superior units and then dehydrated, embedded, and sectioned. H&E staining was used to characterize overall architecture. Collagen orientation and complexity were evaluated via picrosirius-red staining. Safranin-O identified proteoglycan content with additional immunostaining performed to assess Type-II collagen expression. Surprisingly, the ligament along the lateral orbital wall was composed of elastic fibrocartilage. A more degraded organization of collagen fibers in this Postorbital fibrocartilage is correlated with increased masticatory forces due to a more fracture-resistant diet. Furthermore, the lack of marked changes in the extracellular composition of the lateral orbital wall related to tissue viscoelasticity suggests it is unlikely that long-term exposure to elevated masticatory stresses underlies the development of a bony Postorbital Bar.
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PRIMATE ORIGINS: Adaptations and Evolution - PRIMATE ORIGINS: Adaptations and evolution
2007Co-Authors: Matthew J. Ravosa, Marian DagostoAbstract:Supraordinal Relationships of Primates and Their Time of Origin.- A Molecular Classification for the Living Orders of Placental Mammals and the Phylogenetic Placement of Primates.- New Light on the Dates of Primate Origins and Divergence.- The Postcranial Morphology of Ptilocercus lowii (Scandentia, Tupaiidae) and its Implications for Primate Supraordinal Relationships.- Primate Origins: A Reappraisal of Historical Data Favoring Tupaiid Affinities.- Primate Taxonomy, Plesiadapiforms, and Approaches to Primate Origins.- Adaptations and Evolution of the Cranium.- Jaw-Muscle Function and the Origin of Primates.- Were Basal Primates Nocturnal? Evidence From Eye and Orbit Shape.- Oculomotor Stability and the Functions of the Postorbital Bar and Septum.- Primate Origins and the Function of the Circumorbital Region: What's Load Got to Do with It?.- Adaptations and Evolution of the Postcranium.- Origins of Grasping and Locomotor Adaptations in Primates: Comparative and Experimental Approaches Using an Opossum Model.- Evolvability, Limb Morphology, and Primate Origins.- Primate Gaits and Primate Origins.- Morphological Correlates of Forelimb Protraction in Quadrupedal Primates.- Ancestral Locomotor Modes, Placental Mammals, and the Origin of Euprimates: Lessons From History.- The Postcranial Morphotype of Primates.- New Skeletons of Paleocene-Eocene Plesiadapiformes: A Diversity of Arboreal Positional Behaviors in Early Primates.- Adaptations and Evolution of the Brain, Behavior, Physiology, and Ecology.- Start Small and Live Slow: Encephalization, Body Size, and Life History Strategies in Primate Origins and Evolution.- Evolutionary Specializations of Primate Brain Systems.- New Views on the Origin of Primate Social Organization.- Primate Bioenergetics: An Evolutionary Perspective.- Episodic Molecular Evolution of Some Protein Hormones in Primates and Its Implications for Primate Adaptation.- Parallelisms Among Primates and Possums.- Perspectives on Primate Color Vision.
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Masticatory stress, orbital orientation and the evolution of the primate Postorbital Bar.
Journal of human evolution, 2000Co-Authors: Matthew J. Ravosa, William L. Hylander, Vivian E. Noble, Kirk R. Johnson, Erica M. KowalskiAbstract: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.
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Orbit orientation and the function of the mammalian Postorbital Bar
Journal of Zoology, 2000Co-Authors: Vivian E. Noble, Erica M. Kowalski, Matthew J. RavosaAbstract:The visual predation hypothesis of primate origins was introduced by M. Cartmill in the 1970s. In outlining a series of predictions regarding changes in orbital orientation, he further posits that the formation of a bony Postorbital Bar is correlated with greater orbital convergence, which in turn appears to be linked to selection for increased stereoscopic visual acuity in a nocturnal milieu. A series of predictions related to this model is tested in living analogues that vary in Postorbital Bar formation: felid and herpestid carnivorans and the pteropodid megabats. Bivariate correlations and regressions, ANOVA and ANCOVA are used to assess the intrinsic allometric and non-allometric factors thought to affect two aspects of orbital orientation, convergence and frontation. These angles of orbital orientation are then examined in an effort to determine how they are associated with the development of a Postorbital Bar. Cartmill suggested that convergent orbits develop from changes in relative orbit diameter and relative interorbital breadth. This study indicates that felids show only weak support for these predictions, while herpestids do not provide support and pteropodids show some support. Instead, in response to natural selection, convergence seems to develop to improve stereoscopic vision and depth perception in nocturnal predators. As predicted, felids show a significant positive relationship between orbital frontation and relative brain size. Analyses in herpestids, however, do not show significant relationships between frontation and relative palate length or relative brain mass. Pteropodids also do not support the model regarding intrinsic frontation factors. In both carnivoran groups, convergence and frontation are positively correlated, whereas they are not correlated in Pteropodidae. In partial contrast to Cartmill's predictions, we found that orbital convergence and/or orbital frontation are generally higher in carnivorans and bats with Postorbital Bars. Therefore, a greater emphasis on nocturnal stereoscopic visual predation and increased relative brain size both move the orbital aperture out of the plane of the temporal fossa and a Postorbital Bar thus provides adequate rigidity to the lateral orbital margin. In the more encephalized Felidae, orbital frontation is positively correlated with relative brain size; as smaller mammals have relatively larger brains, this explains why Postorbital Bars tend to be found in smaller felids. In herpestids and pteropodids, Postorbital Bars tend to occur in larger taxa which are more convergent than smaller forms.
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Strain in the Galago facial skull
Journal of morphology, 2000Co-Authors: Matthew J. Ravosa, Kirk R. Johnson, William L. HylanderAbstract: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.
Alfred L. Rosenberger - One of the best experts on this subject based on the ideXlab platform.
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Membranous Support for Eyes of Strepsirrhine Primates and Fruit Bats.
Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2016Co-Authors: Brianna M Harvey, Robert Jeffrey Schenck, Valerie Burke Deleon, Susan J. Rehorek, Kunwar P. Bhatnagar, Alfred L. Rosenberger, Anne M Burrows, Timothy D SmithAbstract:: Living primates have relatively large eyes and support orbital tissues with a Postorbital Bar (POB) and/or septum. Some mammals with large eyes lack a POB, and presumably rely on soft tissues. Here, we examined the orbits of four species of strepsirrhine primates (Galagidae, Cheirogaleidae) and three species of fruit bats (Pteropodidae). Microdissection and light microscopy were employed to identify support structures of the orbit. In bats and primates, there are two layers of fascial sheets that border the eye laterally. The outer membrane is the most superficial layer of deep fascia, and has connections to the POB in primates. In fruit bats, which lacked a POB or analogous ligament, the deep fascia is reinforced by transverse ligaments. Bats and primates have a deeper membrane supporting the eye, identified as the periorbita (PA) based on the presence of elastic fibers and smooth muscle. The PA merges with periostea deep within the orbit, but has no periosteal attachment to the POB of primates. These findings demonstrate that relatively big eyes can be supported primarily with fibrous connective tissues as well as the PA, in absence of a POB or ligament. The well-developed smooth muscle component within the PA of fruit bats likely helps to protrude the eye, maintaining a more convergent eye orientation, with greater overlap of the visual fields. The possibility should be considered that early euprimates, and even stem primates that may have lacked a POB, also had more convergent eyes than indicated by osseous measurements of orbital orientation. Anat Rec, 299:1690-1703, 2016. © 2016 Wiley Periodicals, Inc.
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Ontogeny of the Postorbital Region in Tarsiers and Other Primates.
Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2016Co-Authors: Valerie Burke Deleon, Timothy D Smith, Alfred L. RosenbergerAbstract:Bony structure of the Postorbital region is a key trait distinguishing major clades of primates. Strepsirrhines share a Postorbital Bar, and anthropoids share a complete Postorbital septum. At issue is whether the partial Postorbital septum of tarsiers unites living tarsiers more closely with anthropoids than with certain large-eyed Eocene fossils. Previously we reported incomplete Postorbital closure in tarsiers at birth. In this article, we document comparative analyses of the Postorbital region in a broad range of perinatal primates. Virtual reconstructions of microCT data were used to study three-dimensional structure of the perinatal cranium in these taxa. We also describe and illustrate formation of the tarsier partial Postorbital septum through the perinatal period using a growth series of Tarsius syrichta. Our results support the hypothesis that partial Postorbital septation in the tarsier is secondary to eye hypertrophy. Based on these observations, we propose a structural hypothesis for phylogenetic differences observed in the primate Postorbital region. Specifically, we propose that key Postorbital traits, including the frontal spur in strepsirrhines and the posterior lamina of the zygomatic in anthropoids, develop as a result of the spatial relationships of brain, eyes, and teeth. Haplorhines are united by expansion of the anterior cranial fossa and loss of the frontal spur. Anthropoids are further united to the exclusion of tarsiers by expansion of the temporal lobes and associated formation of the posterior lamina of the zygomatic. Mechanical forces related to these spatial relationships may be modulated by deep fascia of the orbit to induce formation of the Postorbital septum. Anat Rec, 299:1631–1645, 2016. © 2016 Wiley Periodicals, Inc.
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Eye Size and Set in Small-Bodied Fossil Primates: A Three-Dimensional Method
Anatomical record (Hoboken N.J. : 2007), 2016Co-Authors: Alfred L. Rosenberger, Valerie Burke Deleon, Timothy D Smith, Anne M Burrows, Robert J. Schenck, Lauren B. HalenarAbstract:We introduce a new method to geometrically reconstruct eye volume and placement in small-bodied primates based on the three-dimensional contour of the intraorbital surface. We validate it using seven species of living primates, with dry skulls and wet dissections, and test its application on seven species of Paleogene fossils of interest. The method performs well even when the orbit is damaged and incomplete, lacking the Postorbital Bar and represented only by the orbital floor. Eye volume is an important quantity for anatomic and metabolic reasons, which due to differences in eye set, or position within (or outside) the bony orbit, can be underestimated in living and fossil forms when calculated from aperture diameter. Our Ectopic Index quantifies how much the globe's volume protrudes anteriorly from the aperture. Lemur, Notharctus and Rooneyia resemble anthropoids, with deeply recessed eyes protruding 11%–13%. Galago and Tarsius are the other extreme, at 47%–56%. We argue that a laterally oriented aperture has little to do with line-of-sight in euprimates, as large ectopic eyes can position the cornea to enable a directly forward viewing axis, and soft tissue positions the eyes facing forward in megachiropteran bats, which have unenclosed, open eye sockets. The size and set of virtual eyes reconstructed from 3D cranial models confirm that eyes were large to hypertrophic in Hemiacodon, Necrolemur, Microchoerus, Pseudoloris and Shoshonius, but eye size in Rooneyia may have been underestimated by measuring the aperture, as in Aotus. Anat Rec, 299:1671–1689, 2016. © 2016 Wiley Periodicals, Inc.
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At Birth, Tarsiers Lack a Postorbital Bar or Septum
Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2013Co-Authors: Timothy D Smith, Valerie Burke Deleon, Alfred L. RosenbergerAbstract:Among primates, partial or complete posterior closure of the orbit has been widely accepted as a shared derived characteristic justifying an exclusive tarsier-anthropoid clade, while some regard the tarsier lateral orbit as an elaborated Postorbital Bar (POB). To test these competing hypotheses while minimizing the confounding effect of tarsier orbital hypertrophy, we compared tarsiers and other primates at early (fetal and newborn) ages using dissection, micro-CT scans and soft tissue histology. Our findings demonstrate unanticipated variation in the anatomy and development of the zygomaticofrontal (ZFA) articulation, which forms the orbit’s lateral framework. Tarsiers uniquely exhibit a combination of two features: absence of a pre- and peri-natal frontal spur to join with the zygomatic to form the ZFA; and, the spur’s substitution by an elaborate ligament, which envelops the eye laterally as an expansive Postorbital membrane (POM) that merges with the anterolateral fontanelle of the lateral cranial vault. In lacking a frontal spur, tarsiers are distinct from strepsirhines, while the ligamentous structure of the POM distinguishes its ZFA from that of anthropoids, which is a typical facial suture at and prior to birth. The POM of tarsiers may be thought of as an accessory fontanelle, a structural compromise that provides flexible stability and spatial separation of bones while anticipating rapid postnatal growth of an enormously enlarged eye. We regard the tarsier POM as part of a neomorphic eyeball hypertrophy complex, and reject the hypothesis of derived homology of the Postorbital septa of adult tarsiers and anthropoids on histological, developmental and functional grounds. Anat Rec, 00:000–000, 2013. V C 2013 Wiley Periodicals, Inc.
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Protoanthropoidea (Primates, Simiiformes): A New Primate Higher Taxon and a Solution to the Rooneyia Problem
Journal of Mammalian Evolution, 2006Co-Authors: Alfred L. RosenbergerAbstract:As a derivative of the hypothesis that anthropoids evolved from omomyid-like primates, the enigmatic North American fossil Rooneyia viejaensis , from the latest Eocene of Texas, is placed in a new higher taxon, Protoanthropoidea, which is proposed as the sister-group of Anthropoidea. Rooneyia and anthropoids share synapomorphically a pattern of character states relating to the unique orbital morphology of higher primates, including; highly convergent and frontated orbits roofed above by an extended frontal bone; funnel-shaped orbital fossae; orbital apices that are recessed beneath the forebrain; a deep, large lateral process of the frontal bone (upper portion of the Postorbital Bar) that may presage closure of the orbit by an enlarged ascending process of the zygomatic. If the sister-group of anthropoids occupied North America as part of a Laurasian geographic distribution during the Paleogene, as some primate genera did, ancestral anthropoids may likewise have occurred across Laurasia, prestaging them to enter Africa and Central/South America in two independent episodes of dispersal—without having the ancestral platyrrhines crossing the daunting Atlantic Ocean.
Bruce S. Rubidge - One of the best experts on this subject based on the ideXlab platform.
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A juvenile specimen of Anteosaurus magnificus Watson, 1921 (Therapsida: Dinocephalia) from the South African Karoo, and its implications for understanding dinocephalian ontogeny
Journal of Systematic Palaeontology, 2017Co-Authors: Ashley Kruger, Bruce S. Rubidge, Fernando AbdalaAbstract:Anteosaurid dinocephalians were the apex terrestrial predators of the latter part of the Guadalupian (middle Permian) and became extinct at the end of that epoch. The group was relatively diverse in Russia, but represented by only two genera, Australosyodon and Anteosaurus, in the Karoo rocks of South Africa. A newly discovered skull of Anteosaurus magnificus from the Abrahamskraal Formation is unique among specimens of this taxon in having most of the individual cranial bones disarticulated, permitting accurate delimitation of cranial sutures for the first time. The relatively large orbits and unfused nature of the cranial sutures suggest juvenile status for the specimen. A computer-aided 3D reconstruction of the skull, and comparison with 11 additional individuals, enabled an allometric study of cranial growth in the species. Positive allometry for four of the measurements suggests rapid growth in the temporal region, and a significant difference in the development of the Postorbital Bar and suborbital ...
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New Material of Microgomphodon oligocynus (Eutherapsida, Therocephalia) and the Taxonomy of Southern African Bauriidae
Vertebrate Paleobiology and Paleoanthropology, 2013Co-Authors: Fernando Abdala, Bruce S. Rubidge, Tea Jashashvili, Juri Van Den HeeverAbstract:An exceptionally well-preserved specimen of the bauriid therocephalian Microgomphodon oligocynus from the Burgersdorp Formation (Early-Middle Triassic, Cynognathus Assemblage Zone) of the South African Karoo is described. In addition, a taxonomic revision of bauriid therocephalians from southern Africa, based on firsthand examination of almost all know specimens, is presented. Microgomphodon oligocynus and Bauria cynops are recognized as the only valid species of southern African bauriids. Microgomphodon oligocynus is differentiated from B. cynops on the basis of clear-cut morphological features such as the presence of a complete Postorbital Bar, pineal foramen, contribution of the vomer to the osseous secondary palate, comparatively large orbits, presence of a lateral fossa on the posterior portion of the horizontal ramus and on the coronoid process of the dentary, and reduced number of postcanines. Procrustes analysis of the two best-preserved specimens of these species allowed recognition of further shape differences: M. oligocynus has a taller but narrower cranium, taller snout, temporal opening more expanded laterally, pterygoid process located more anteriorly, and smaller suborbital vacuity. The mandible of M. oligocynus has a higher symphysis, relatively short corpus, and more laterally-directed coronoid process. Microgomphodon oligocynus is known from the Olenekian to what are probably late Anisian levels in South Africa and Namibia, whereas B. cynops is restricted to the early Anisian of South Africa.
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Skeletal morphology, phylogenetic relationships and stratigraphic range of Eosimops newtoni Broom, 1921, a pylaecephalid dicynodont (Therapsida, Anomodontia) from the Middle Permian of South Africa
Journal of Systematic Palaeontology, 2012Co-Authors: Kenneth D. Angielczyk, Bruce S. RubidgeAbstract:Robert Broom described Eosimops newtoni in 1921 based on a skull collected in Tapinocephalus Assemblage Zone strata in South Africa, and the species has been largely overlooked since that time. Here we present several new specimens of E. newtoni, including a nearly complete skeleton, that allow a much more thorough description of its morphology. Eosimops newtoni is diagnosed by two autapomorphies, a Postorbital Bar that is anteroposteriorly expanded in lateral view and a posterior median palatal ridge that forms a flattened, Y-shaped platform surrounding the anterior median palatal ridges. Other characters include a single median nasal boss; parietals widely exposed on the skull roof; presence of lateral anterior palatal ridges; anterior edge of caniniform process set off from the palatal rim forming a notch; a small number of ‘postcanine' teeth on the maxilla; a large, ventrally directed transverse flange on the anterior pterygoid ramus; a robust, tall, blocky crista oesophagea; a shovel-shaped jaw symph...
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A new Burnetiamorph (Therapsida: Biarmosuchia) from the Middle Permian of South Africa
Journal of Paleontology, 2006Co-Authors: Bruce S. Rubidge, Christian A. Sidor, Sean P. ModestoAbstract:Abstract The skull of a carnivorous therapsid from the Tapinocephalus Assemblage Zone of the Beaufort Group, Middle Permian of South Africa, is described as a new burnetiamorph biarmosuchian. Pachydectes elsi n. gen. and sp. is distinguished from all other therapsids by its possession of a conspicuous pachyostotic maxillary boss that sheathes the root of the upper canine. It shares the presence of a preparietal ossification with other biarmosuchians and a pachyostotic boss below the Postorbital Bar with other burnetiamorphs. Pachydectes is the first burnetiamorph known from along the Ecca-Beaufort contact in the eastern part of the Karoo Basin and only the second burnetiamorph to be described from the Tapinocephalus Assemblage Zone. All other South African burnetiamorphs, save Bullacephalus jacksoni, are known from much younger biozones of the Beaufort Group. Our phylogenetic analysis links Pachydectes and Bullacephalus, which are the stratigraphically lowest-occurring taxa, with Burnetia, the burnetiamor...
William L. Hylander - One of the best experts on this subject based on the ideXlab platform.
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Strain in the Galago facial skull
Journal of morphology, 2000Co-Authors: Matthew J. Ravosa, Kirk R. Johnson, William L. HylanderAbstract: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.
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Masticatory stress, orbital orientation and the evolution of the primate Postorbital Bar.
Journal of human evolution, 2000Co-Authors: Matthew J. Ravosa, William L. Hylander, Vivian E. Noble, Kirk R. Johnson, Erica M. KowalskiAbstract: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.
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In vivo and in vitro bone strain in the owl monkey circumorbital region and the function of the Postorbital septum.
American Journal of Physical Anthropology, 1996Co-Authors: Callum F. Ross, William L. HylanderAbstract:Anthropoids and tarsiers are the only vertebrates possessing a Postorbital septum. This septum, formed by the frontal, alisphenoid, and zygomatic bones, separates the orbital contents from the temporal muscles. Three hypotheses suggest that the Postorbital septum evolved to resist stresses acting on the skull during mastication or incision. The facial-torsion hypothesis posits that the septum resists twisting of the face about a rostrocaudal axis during unilateral mastication; the transverse-bending hypothesis argues that the septum resists caudally directed forces acting at the lateral orbital margin during mastication or incision; and the tension hypothesis suggests that the septum resists ventrally directed components of masseter muscle force during mastication and incision. This study evaluates these hypotheses using in vitro and in vivo bone strain data recorded from the circumorbital region of owl monkeys. Incisor loading of an owl monkey skull in vitro bends the face upward in the sagittal plane, compressing the interorbital region rostrocaudally and buckling the lateral orbital walls. Unilateral loading of the toothrow in vitro also bends the face in the sagittal plane, compressing the interorbital region rostrocaudally and buckling the working side lateral orbital wall. When the lateral orbital wall is partially cut, so as to reduce the width of its attachment to the braincase, the following changes in circumorbital bone strain patterns occur. During loading of the incisors, lower bone strain magnitudes are recorded in the interorbital region and lateral orbital walls. In contrast, during unilateral loading of the P 3 , higher bone strain magnitudes are observed in the interorbital region, and generally lower bone strain magnitudes are observed in the lateral orbital walls. During unilateral loading of the M 2 , higher bone strain magnitudes are observed in both the interorbital region and in the lateral orbital wall ipsilateral to the loaded molar. Comparisons of the in vitro results with data gathered in vivo suggest that, during incision and unilateral mastication, the face is subjected to upward bending in the sagittal plane resulting in rostrocaudal compression of the interorbital region. Modeling the lateral orbital walls as curved plates suggests that during mastication the working side wall is buckled due to the dorsally directed component of the maxillary bite force which causes upward bending of the face in the sagittal plane. The balancing side lateral orbital wall may also be buckled due to upward bending of the face in the sagittal plane as well as being twisted by the caudoventrally directed components of the superficial masseter muscle force. The in vivo data do not exclude the possibility that the Postorbital septum functions to improve the structural integrity of the Postorbital Bar during mastication. However, there is no reason to believe that a more robust Postorbital Bar could not also perform this function. Hypotheses stating that the Postorbital septum originally evolved to reinforce the skull against routine masticatory loads must explain why, rather than evolving a Postorbital septum, the stem anthropoids did not simply enlarge their Postorbital Bars.
Erica M. Kowalski - One of the best experts on this subject based on the ideXlab platform.
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Masticatory stress, orbital orientation and the evolution of the primate Postorbital Bar.
Journal of human evolution, 2000Co-Authors: Matthew J. Ravosa, William L. Hylander, Vivian E. Noble, Kirk R. Johnson, Erica M. KowalskiAbstract: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.
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Orbit orientation and the function of the mammalian Postorbital Bar
Journal of Zoology, 2000Co-Authors: Vivian E. Noble, Erica M. Kowalski, Matthew J. RavosaAbstract:The visual predation hypothesis of primate origins was introduced by M. Cartmill in the 1970s. In outlining a series of predictions regarding changes in orbital orientation, he further posits that the formation of a bony Postorbital Bar is correlated with greater orbital convergence, which in turn appears to be linked to selection for increased stereoscopic visual acuity in a nocturnal milieu. A series of predictions related to this model is tested in living analogues that vary in Postorbital Bar formation: felid and herpestid carnivorans and the pteropodid megabats. Bivariate correlations and regressions, ANOVA and ANCOVA are used to assess the intrinsic allometric and non-allometric factors thought to affect two aspects of orbital orientation, convergence and frontation. These angles of orbital orientation are then examined in an effort to determine how they are associated with the development of a Postorbital Bar. Cartmill suggested that convergent orbits develop from changes in relative orbit diameter and relative interorbital breadth. This study indicates that felids show only weak support for these predictions, while herpestids do not provide support and pteropodids show some support. Instead, in response to natural selection, convergence seems to develop to improve stereoscopic vision and depth perception in nocturnal predators. As predicted, felids show a significant positive relationship between orbital frontation and relative brain size. Analyses in herpestids, however, do not show significant relationships between frontation and relative palate length or relative brain mass. Pteropodids also do not support the model regarding intrinsic frontation factors. In both carnivoran groups, convergence and frontation are positively correlated, whereas they are not correlated in Pteropodidae. In partial contrast to Cartmill's predictions, we found that orbital convergence and/or orbital frontation are generally higher in carnivorans and bats with Postorbital Bars. Therefore, a greater emphasis on nocturnal stereoscopic visual predation and increased relative brain size both move the orbital aperture out of the plane of the temporal fossa and a Postorbital Bar thus provides adequate rigidity to the lateral orbital margin. In the more encephalized Felidae, orbital frontation is positively correlated with relative brain size; as smaller mammals have relatively larger brains, this explains why Postorbital Bars tend to be found in smaller felids. In herpestids and pteropodids, Postorbital Bars tend to occur in larger taxa which are more convergent than smaller forms.