Papers by Jana Makedonska
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This paper describes the initial findings of the Balkan Paleo Project (BPP). The project seeks: 1... more This paper describes the initial findings of the Balkan Paleo Project (BPP). The project seeks: 1 – to augment the evidence that can be used to test hypotheses about hominin and faunal dispersals into and out of Europe during the Pleistocene; 2 – to gather data for testing the hypotheses regarding the adaptation of early human populations to Eurasian ecosystems, the adjustment of their tool technologies, anatomical characteristics and behaviors in response to local climates and faunal evidence. These research objectives can only be achieved by identifying and excavating a broad spectrum of archaeological and paleontological sties that span the Pleistocene within the Balkan Peninsula. Results of BPP activities conducted in southern Bulgaria are reported here. These include excavations at the Arkata rockshelter and associated caves overlooking the Arda River near (Eastern Rhodopes, Krumovgrad district), the Leyarna caves and the previously known paleontological locality of Mechata Dup...
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Background
The tools and techniques used in morphometrics have always aimed to transform the phy... more Background
The tools and techniques used in morphometrics have always aimed to transform the physical shape of an object into a concise set of numerical data for mathematical analysis. The advent of landmark-based morphometrics opened new avenues of research, but these methods are not without drawbacks. The time investment required of trained individuals to accurately landmark a data set is significant, and the reliance on readily-identifiable physical features can hamper research efforts. This is especially true of those investigating smooth or featureless surfaces.
Methods
In this paper, we present a new method to perform this transformation for data obtained from high-resolution scanning technology. This method uses surface scans, instead of landmarks, to calculate a shape difference metric analogous to Procrustes distance and perform superimposition. This is accomplished by building upon and extending the Iterative Closest Point algorithm. We also explore some new ways this data can be used; for example, we can calculate an averaged surface directly and visualize point-wise shape information over this surface. Finally, we briefly demonstrate this method on a set of primate skulls and compare the results of the new methodology with traditional geometric morphometric analysis.
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Two trenches excavated at Magura Cave, north-west Bulgaria, have provided Late Pleistocene lithic... more Two trenches excavated at Magura Cave, north-west Bulgaria, have provided Late Pleistocene lithic artefacts as well as environmental evidence in the form of large and small mammals, herpetofauna and pollen recovered from Crocuta coprolites. One of the trenches also has a visible tephra layer which has been confirmed as representing the major Campanian Ignimbrite eruption and is accurately dated at the source area to 39,280 ± 55 yrs and radiocarbon determinations have added to chronological resolution at the site. The palaeoenvironment of the region during the Late Pleistocene is discussed in the context of hominin presence and shows a mosaic landscape in a region considered a crucial refugium for both plants and mammals, including hominins.
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In complex organisms, suites of non-random, highly intercorrelated phenotypic traits, organized a... more In complex organisms, suites of non-random, highly intercorrelated phenotypic traits, organized according to their developmental history and forming semi-autonomous units (i.e. modules), have the potential to impose constraints on morphological diversification or to improve evolvability. Because of its structural, developmental and functional complexity, the cranium is arguably one of the best models for studying the interplay between developmental history and the need for various parts of a structure to specialize in different functions.
This study evaluated the significance of two specific types of developmental imprints in the adult anthropoid cranium, those imposed by ossification pattern (i.e. ossification with and without a pre-existing cartilaginous phase) and those imposed by tissue origin (i.e. tissues derived principally from neural-crest vs. those derived from paraxial mesoderm). Specifically, this study tests the hypothesis that the face and the basicranium form two distinct modules with higher within-unit trait integration magnitudes compared with the cranium as a whole.
Data on 12 anthropoid primate species were collected in the form of 20 3-dimensional landmarks digitized on cranial surface models that sample the basicranium as well as regions of functional importance during feeding. The presence of a significant modularity imprint in the adult cranium was assessed using a between-region within-species comparison of multivariate correlations (RV coefficients) obtained with partial least-squares, using within-module within-species eigenvalue variance (EV), and using cluster analyses and non-metric multidimensional scaling. In addition to addressing the validity of the cranial modularity hypothesis in anthropoids, this study addressed methodological aspects of the interspecific comparison of morphological integration, namely the effect of sample size and the effect of landmark number on integration magnitudes.
Two methodological findings that are of significance to research in morphological integration are that: (i) a smaller sample size increases integration magnitude, but preserves the pattern of variation of integration magnitudes from block to block within species; and that (ii) the number of landmarks per cranial block does not significantly impact block integration magnitude measured as EV.
Results from the analyses testing for cranial modularity imprints in the adult anthropoid cranium show that some facial landmarks covary more strongly with basicranial landmarks than with other facial landmarks. Cluster methods, non-metric multidimensional scaling and, to an extent, RV results show that the rostral and the zygomatic landmarks covary more strongly with the basicranial landmarks than they do with the molar landmarks. However, the rostral–zygomatic–basicranial block, the molar block, the facial block, the basicranial block and the other analyzed cranial and facial blocks are not more integrated than the cranium. Thus, the morphological variation in the adult anthropoid cranium is not significantly constrained by at least two of the potential developmental sources of its covariance structure.
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A fundamental challenge of morphology is to identify the underlying evolutionary and developmenta... more A fundamental challenge of morphology is to identify the underlying evolutionary and developmental mechanisms leading to correlated phenotypic characters. Patterns and magnitudes of morphological integration and their association with environmental variables are essential for understanding the evolution of complex phenotypes, yet the nature of the relevant selective pressures remains poorly understood.
In this study, the adaptive significance of morphological integration was evaluated through the association between feeding mechanics, ingestive behavior and craniofacial variation. Five capuchin species were examined, Cebus apella sensu stricto, Cebus libidinosus, Cebus nigritus, Cebus olivaceus and Cebus albifrons.
Twenty three-dimensional landmarks were chosen to sample facial regions experiencing high strains during feeding, characteristics affecting muscular mechanical advantage and basicranial regions. Integration structure and magnitude between and within the oral and zygomatic subunits, between and within blocks maximizing modularity and within the face, the basicranium and the cranium were examined using partial-least squares, eigenvalue variance, integration indices compared inter-specifically at a common level of sampled population variance and cluster analyses.
Results are consistent with previous findings reporting a relative constancy of facial and cranial correlation patterns across mammals, while covariance magnitudes vary.
Results further suggest that food material properties structure integration among functionally-linked facial elements and possibly integration between the face and the basicranium. Hard-object-feeding capuchins, especially C.apella s.s., whose faces experience particularly high biomechanical loads are characterized by higher facial and cranial integration especially compared to C.albifrons, likely because morphotypes compromising feeding performance are selected against in species relying on obdurate fallback foods.
This is the first study to report a link between food material properties and facial and cranial integration. Furthermore, results do not identify the consistent presence of cranial modules yielding support to suggestions that despite the distinct embryological imprints of its elements the cranium of placental mammals is not characterized by a modular architecture.
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Hypothesis testing is used to guide scientific
research by narrowing down possible explanations
f... more Hypothesis testing is used to guide scientific
research by narrowing down possible explanations
for a phenomenon, using the principle of elimination
of alternative scenarios. Thus, scientists
test hypotheses by attempting to falsify them.
A hypothesis is deduced from observed patterns
and aims at linking those patterns to the factors
proposed to have caused it. Hypothesis testing is
frequently accompanied by statistical tests of null
hypotheses, focusing on the inferential analysis
of sample properties such as the mean and the
variance. For instance, if there is less than a 5%
chance that two samples are drawn from the same
entity, we reject the null hypothesis and claim that
these samples are significantly different. A salient
point to keep in mind when testing hypotheses
is that a successful evaluation of a hypothesis
depends critically on the manner in which it was
formulated. Hypotheses pertaining to the origin
of modern humans are reviewed and evaluated.
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A central topic in human evolution pertains to
the emergence of habitual bipedalism [i.e., uprig... more A central topic in human evolution pertains to
the emergence of habitual bipedalism [i.e., upright
walking (UW)], a behavioural characteristic that
defines the human lineage and is unique among
primates. To pinpoint the factors that led to the
appearance of UW, one has to reconstruct the locomotor
behaviour of the last common ancestor of
humans and their closest living relatives, the chimpanzees.
Chimpanzees and gorillas adopt a peculiar
mode of locomotion when travelling on the
ground, knuckle-walking (KW). This article evaluates
the evidence for and against the hypothesis
that humans have descended from a KW ancestor.
The conflicting nature of this evidence does
not allow firm conclusions, but future avenues of
research are proposed.
Bookmarks Related papers MentionsView impact
Conference Presentations by Jana Makedonska
In mammals, the inside of the braincase is molded by the brain so that an internal cast of the br... more In mammals, the inside of the braincase is molded by the brain so that an internal cast of the braincase (=an endocast) duplicates, with more or less clarity, the external anatomy of the brain (Radinsky, 1972). The advent of CT technology, on the other hand, has revolutionized the collection of data on internal biological structures, such as the vertebrate endocranial morphology. For these reasons, numerous authors suggested the potential for incorporating these data into phylogenetic analyses and for inferring the degree of evolution of different sensory and motor systems associated with the brains of modern and extinct taxa.
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This study aims to directly evaluate the adaptive significance of morphological integration by ... more This study aims to directly evaluate the adaptive significance of morphological integration by testing for the existence of a causal link between feeding biomechanics and patterned variation in the masticatory apparatus, with a focus on the effect of mechanical constraints imposed by diet. Although the functional utility of integration is implicitly assumed, to our knowledge this will be the first attempt to systematically assess its ecological determinants.
HYPOTHESES
Two sets of hypotheses named food-material-properties (HFMP) and heterochrony (HHET) hypotheses are tested.
HFMP0: Predicts no consistent differences in the patterns and/or intensities of morphological integration between species whose faces experience significantly different biomechanical loads.
HFMP1: Predicts that species relying on selectively important but mechanically resistant foods will have more strongly morphologically integrated faces than species lacking such adaptations.
HFMP2: Predicts the opposite of HFMP1.
HHET0: Predicts no consistent differences in facial integration between the sexes.
HHET1: Predicts that males in dimorphic species will display higher levels of facial integration than conspecific females.
HHET2: Predicts the opposite of HHET1.
BACKGROUND TO HYPOTHESES
HFMP1 expects that facial morphologies which compromise feeding performance and thus have a negative impact on fitness will be selected against resulting in the spread of a functionally advantageous pattern in the population, and by extension in an increase in integration intensity. Such adaptation could also affect the number of functionally-linked elements, since when bite force increases more regions will be subjected to high magnitude strain (Hylander, 1977). The premise of HFMP1 is justified by: 1) numerous studies suggesting that the face, particularly its oral and zygomatic subunits, is the module contributing most extensively to cranial integration in primates (e.g., Marroig and Cheverud, 2001; Ackermann, 2005); 2) reports indicating that groups of mice and primates fed artificially soft diets during development exhibit increased morphological variability and decreased dentognathic integration relative to groups fed harder diets (Beecher and Corruccini, 1981; Beecher et al., 1983; Corruccini and Beecher, 1984).
HFMP2 represents an extrapolation of the Wood-and-Lieberman-2001 hypothesis, which postulates that skeletal structures subject to high or frequent magnitudes of masticatory strain would be more variable within species than those subjected to lower strain magnitudes. One might extrapolate from this hypothesis that if epigenetic stimuli increase variation, that process might also decrease covariance among traits. The hypotheses expecting integration to be sexually dimorphic follow logically from the observations that the face does not terminate its growth until early adulthood (Enlow and Hans, 1996), while growth spurts are sex-dependent (Leigh, 1992). An expectation of HHET1 would further be that integration increa
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Craniofacial sutures are major sites of bone expansion during postnatal skull growth (Opperman,... more Craniofacial sutures are major sites of bone expansion during postnatal skull growth (Opperman, 2000). It is generally thought that the growth and morphology of craniofacial
sutures reflect their functional environment (Rafferty and Herring, 1999). Craniofacial sutures can be viewed weak bone “growth” sites characterized by very different material
properties than the surrounding rigid skull bones; thence they must be shielded from unduly high stresses so as not to disrupt vital growth processes and skeletal functions.
Thus, it is hypothesized that the placement of craniofacial sutures should maximize their growth potentials yet minimize their negative biomechanical impacts, especially in areas
under high stress during dietary activities, such as the midface. Specifically, for any given suture, it is hypothesized that suture position would be different in skulls of different form
and/or adapted to different dietary ecology.
In this pilot study, we investigated the position of the Maxillo-Zygomatic suture (MZS) and the covariance patterns between zygomatic bone 3D sutural and geometric landmarks in a sample including Old World Monkeys (OWMs) and New World Monkeys (NWMs) with the aim to identify phylogenetic (including allometric) effects and distinctions among dietary groups. Further, we studied the association of the zygomatic bone with maxillary and premaxillary traits and neurocranial traits.
Bookmarks Related papers MentionsView impact
Teaching Documents by Jana Makedonska
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Papers by Jana Makedonska
The tools and techniques used in morphometrics have always aimed to transform the physical shape of an object into a concise set of numerical data for mathematical analysis. The advent of landmark-based morphometrics opened new avenues of research, but these methods are not without drawbacks. The time investment required of trained individuals to accurately landmark a data set is significant, and the reliance on readily-identifiable physical features can hamper research efforts. This is especially true of those investigating smooth or featureless surfaces.
Methods
In this paper, we present a new method to perform this transformation for data obtained from high-resolution scanning technology. This method uses surface scans, instead of landmarks, to calculate a shape difference metric analogous to Procrustes distance and perform superimposition. This is accomplished by building upon and extending the Iterative Closest Point algorithm. We also explore some new ways this data can be used; for example, we can calculate an averaged surface directly and visualize point-wise shape information over this surface. Finally, we briefly demonstrate this method on a set of primate skulls and compare the results of the new methodology with traditional geometric morphometric analysis.
This study evaluated the significance of two specific types of developmental imprints in the adult anthropoid cranium, those imposed by ossification pattern (i.e. ossification with and without a pre-existing cartilaginous phase) and those imposed by tissue origin (i.e. tissues derived principally from neural-crest vs. those derived from paraxial mesoderm). Specifically, this study tests the hypothesis that the face and the basicranium form two distinct modules with higher within-unit trait integration magnitudes compared with the cranium as a whole.
Data on 12 anthropoid primate species were collected in the form of 20 3-dimensional landmarks digitized on cranial surface models that sample the basicranium as well as regions of functional importance during feeding. The presence of a significant modularity imprint in the adult cranium was assessed using a between-region within-species comparison of multivariate correlations (RV coefficients) obtained with partial least-squares, using within-module within-species eigenvalue variance (EV), and using cluster analyses and non-metric multidimensional scaling. In addition to addressing the validity of the cranial modularity hypothesis in anthropoids, this study addressed methodological aspects of the interspecific comparison of morphological integration, namely the effect of sample size and the effect of landmark number on integration magnitudes.
Two methodological findings that are of significance to research in morphological integration are that: (i) a smaller sample size increases integration magnitude, but preserves the pattern of variation of integration magnitudes from block to block within species; and that (ii) the number of landmarks per cranial block does not significantly impact block integration magnitude measured as EV.
Results from the analyses testing for cranial modularity imprints in the adult anthropoid cranium show that some facial landmarks covary more strongly with basicranial landmarks than with other facial landmarks. Cluster methods, non-metric multidimensional scaling and, to an extent, RV results show that the rostral and the zygomatic landmarks covary more strongly with the basicranial landmarks than they do with the molar landmarks. However, the rostral–zygomatic–basicranial block, the molar block, the facial block, the basicranial block and the other analyzed cranial and facial blocks are not more integrated than the cranium. Thus, the morphological variation in the adult anthropoid cranium is not significantly constrained by at least two of the potential developmental sources of its covariance structure.
In this study, the adaptive significance of morphological integration was evaluated through the association between feeding mechanics, ingestive behavior and craniofacial variation. Five capuchin species were examined, Cebus apella sensu stricto, Cebus libidinosus, Cebus nigritus, Cebus olivaceus and Cebus albifrons.
Twenty three-dimensional landmarks were chosen to sample facial regions experiencing high strains during feeding, characteristics affecting muscular mechanical advantage and basicranial regions. Integration structure and magnitude between and within the oral and zygomatic subunits, between and within blocks maximizing modularity and within the face, the basicranium and the cranium were examined using partial-least squares, eigenvalue variance, integration indices compared inter-specifically at a common level of sampled population variance and cluster analyses.
Results are consistent with previous findings reporting a relative constancy of facial and cranial correlation patterns across mammals, while covariance magnitudes vary.
Results further suggest that food material properties structure integration among functionally-linked facial elements and possibly integration between the face and the basicranium. Hard-object-feeding capuchins, especially C.apella s.s., whose faces experience particularly high biomechanical loads are characterized by higher facial and cranial integration especially compared to C.albifrons, likely because morphotypes compromising feeding performance are selected against in species relying on obdurate fallback foods.
This is the first study to report a link between food material properties and facial and cranial integration. Furthermore, results do not identify the consistent presence of cranial modules yielding support to suggestions that despite the distinct embryological imprints of its elements the cranium of placental mammals is not characterized by a modular architecture.
research by narrowing down possible explanations
for a phenomenon, using the principle of elimination
of alternative scenarios. Thus, scientists
test hypotheses by attempting to falsify them.
A hypothesis is deduced from observed patterns
and aims at linking those patterns to the factors
proposed to have caused it. Hypothesis testing is
frequently accompanied by statistical tests of null
hypotheses, focusing on the inferential analysis
of sample properties such as the mean and the
variance. For instance, if there is less than a 5%
chance that two samples are drawn from the same
entity, we reject the null hypothesis and claim that
these samples are significantly different. A salient
point to keep in mind when testing hypotheses
is that a successful evaluation of a hypothesis
depends critically on the manner in which it was
formulated. Hypotheses pertaining to the origin
of modern humans are reviewed and evaluated.
the emergence of habitual bipedalism [i.e., upright
walking (UW)], a behavioural characteristic that
defines the human lineage and is unique among
primates. To pinpoint the factors that led to the
appearance of UW, one has to reconstruct the locomotor
behaviour of the last common ancestor of
humans and their closest living relatives, the chimpanzees.
Chimpanzees and gorillas adopt a peculiar
mode of locomotion when travelling on the
ground, knuckle-walking (KW). This article evaluates
the evidence for and against the hypothesis
that humans have descended from a KW ancestor.
The conflicting nature of this evidence does
not allow firm conclusions, but future avenues of
research are proposed.
Conference Presentations by Jana Makedonska
HYPOTHESES
Two sets of hypotheses named food-material-properties (HFMP) and heterochrony (HHET) hypotheses are tested.
HFMP0: Predicts no consistent differences in the patterns and/or intensities of morphological integration between species whose faces experience significantly different biomechanical loads.
HFMP1: Predicts that species relying on selectively important but mechanically resistant foods will have more strongly morphologically integrated faces than species lacking such adaptations.
HFMP2: Predicts the opposite of HFMP1.
HHET0: Predicts no consistent differences in facial integration between the sexes.
HHET1: Predicts that males in dimorphic species will display higher levels of facial integration than conspecific females.
HHET2: Predicts the opposite of HHET1.
BACKGROUND TO HYPOTHESES
HFMP1 expects that facial morphologies which compromise feeding performance and thus have a negative impact on fitness will be selected against resulting in the spread of a functionally advantageous pattern in the population, and by extension in an increase in integration intensity. Such adaptation could also affect the number of functionally-linked elements, since when bite force increases more regions will be subjected to high magnitude strain (Hylander, 1977). The premise of HFMP1 is justified by: 1) numerous studies suggesting that the face, particularly its oral and zygomatic subunits, is the module contributing most extensively to cranial integration in primates (e.g., Marroig and Cheverud, 2001; Ackermann, 2005); 2) reports indicating that groups of mice and primates fed artificially soft diets during development exhibit increased morphological variability and decreased dentognathic integration relative to groups fed harder diets (Beecher and Corruccini, 1981; Beecher et al., 1983; Corruccini and Beecher, 1984).
HFMP2 represents an extrapolation of the Wood-and-Lieberman-2001 hypothesis, which postulates that skeletal structures subject to high or frequent magnitudes of masticatory strain would be more variable within species than those subjected to lower strain magnitudes. One might extrapolate from this hypothesis that if epigenetic stimuli increase variation, that process might also decrease covariance among traits. The hypotheses expecting integration to be sexually dimorphic follow logically from the observations that the face does not terminate its growth until early adulthood (Enlow and Hans, 1996), while growth spurts are sex-dependent (Leigh, 1992). An expectation of HHET1 would further be that integration increa
sutures reflect their functional environment (Rafferty and Herring, 1999). Craniofacial sutures can be viewed weak bone “growth” sites characterized by very different material
properties than the surrounding rigid skull bones; thence they must be shielded from unduly high stresses so as not to disrupt vital growth processes and skeletal functions.
Thus, it is hypothesized that the placement of craniofacial sutures should maximize their growth potentials yet minimize their negative biomechanical impacts, especially in areas
under high stress during dietary activities, such as the midface. Specifically, for any given suture, it is hypothesized that suture position would be different in skulls of different form
and/or adapted to different dietary ecology.
In this pilot study, we investigated the position of the Maxillo-Zygomatic suture (MZS) and the covariance patterns between zygomatic bone 3D sutural and geometric landmarks in a sample including Old World Monkeys (OWMs) and New World Monkeys (NWMs) with the aim to identify phylogenetic (including allometric) effects and distinctions among dietary groups. Further, we studied the association of the zygomatic bone with maxillary and premaxillary traits and neurocranial traits.
Teaching Documents by Jana Makedonska
The tools and techniques used in morphometrics have always aimed to transform the physical shape of an object into a concise set of numerical data for mathematical analysis. The advent of landmark-based morphometrics opened new avenues of research, but these methods are not without drawbacks. The time investment required of trained individuals to accurately landmark a data set is significant, and the reliance on readily-identifiable physical features can hamper research efforts. This is especially true of those investigating smooth or featureless surfaces.
Methods
In this paper, we present a new method to perform this transformation for data obtained from high-resolution scanning technology. This method uses surface scans, instead of landmarks, to calculate a shape difference metric analogous to Procrustes distance and perform superimposition. This is accomplished by building upon and extending the Iterative Closest Point algorithm. We also explore some new ways this data can be used; for example, we can calculate an averaged surface directly and visualize point-wise shape information over this surface. Finally, we briefly demonstrate this method on a set of primate skulls and compare the results of the new methodology with traditional geometric morphometric analysis.
This study evaluated the significance of two specific types of developmental imprints in the adult anthropoid cranium, those imposed by ossification pattern (i.e. ossification with and without a pre-existing cartilaginous phase) and those imposed by tissue origin (i.e. tissues derived principally from neural-crest vs. those derived from paraxial mesoderm). Specifically, this study tests the hypothesis that the face and the basicranium form two distinct modules with higher within-unit trait integration magnitudes compared with the cranium as a whole.
Data on 12 anthropoid primate species were collected in the form of 20 3-dimensional landmarks digitized on cranial surface models that sample the basicranium as well as regions of functional importance during feeding. The presence of a significant modularity imprint in the adult cranium was assessed using a between-region within-species comparison of multivariate correlations (RV coefficients) obtained with partial least-squares, using within-module within-species eigenvalue variance (EV), and using cluster analyses and non-metric multidimensional scaling. In addition to addressing the validity of the cranial modularity hypothesis in anthropoids, this study addressed methodological aspects of the interspecific comparison of morphological integration, namely the effect of sample size and the effect of landmark number on integration magnitudes.
Two methodological findings that are of significance to research in morphological integration are that: (i) a smaller sample size increases integration magnitude, but preserves the pattern of variation of integration magnitudes from block to block within species; and that (ii) the number of landmarks per cranial block does not significantly impact block integration magnitude measured as EV.
Results from the analyses testing for cranial modularity imprints in the adult anthropoid cranium show that some facial landmarks covary more strongly with basicranial landmarks than with other facial landmarks. Cluster methods, non-metric multidimensional scaling and, to an extent, RV results show that the rostral and the zygomatic landmarks covary more strongly with the basicranial landmarks than they do with the molar landmarks. However, the rostral–zygomatic–basicranial block, the molar block, the facial block, the basicranial block and the other analyzed cranial and facial blocks are not more integrated than the cranium. Thus, the morphological variation in the adult anthropoid cranium is not significantly constrained by at least two of the potential developmental sources of its covariance structure.
In this study, the adaptive significance of morphological integration was evaluated through the association between feeding mechanics, ingestive behavior and craniofacial variation. Five capuchin species were examined, Cebus apella sensu stricto, Cebus libidinosus, Cebus nigritus, Cebus olivaceus and Cebus albifrons.
Twenty three-dimensional landmarks were chosen to sample facial regions experiencing high strains during feeding, characteristics affecting muscular mechanical advantage and basicranial regions. Integration structure and magnitude between and within the oral and zygomatic subunits, between and within blocks maximizing modularity and within the face, the basicranium and the cranium were examined using partial-least squares, eigenvalue variance, integration indices compared inter-specifically at a common level of sampled population variance and cluster analyses.
Results are consistent with previous findings reporting a relative constancy of facial and cranial correlation patterns across mammals, while covariance magnitudes vary.
Results further suggest that food material properties structure integration among functionally-linked facial elements and possibly integration between the face and the basicranium. Hard-object-feeding capuchins, especially C.apella s.s., whose faces experience particularly high biomechanical loads are characterized by higher facial and cranial integration especially compared to C.albifrons, likely because morphotypes compromising feeding performance are selected against in species relying on obdurate fallback foods.
This is the first study to report a link between food material properties and facial and cranial integration. Furthermore, results do not identify the consistent presence of cranial modules yielding support to suggestions that despite the distinct embryological imprints of its elements the cranium of placental mammals is not characterized by a modular architecture.
research by narrowing down possible explanations
for a phenomenon, using the principle of elimination
of alternative scenarios. Thus, scientists
test hypotheses by attempting to falsify them.
A hypothesis is deduced from observed patterns
and aims at linking those patterns to the factors
proposed to have caused it. Hypothesis testing is
frequently accompanied by statistical tests of null
hypotheses, focusing on the inferential analysis
of sample properties such as the mean and the
variance. For instance, if there is less than a 5%
chance that two samples are drawn from the same
entity, we reject the null hypothesis and claim that
these samples are significantly different. A salient
point to keep in mind when testing hypotheses
is that a successful evaluation of a hypothesis
depends critically on the manner in which it was
formulated. Hypotheses pertaining to the origin
of modern humans are reviewed and evaluated.
the emergence of habitual bipedalism [i.e., upright
walking (UW)], a behavioural characteristic that
defines the human lineage and is unique among
primates. To pinpoint the factors that led to the
appearance of UW, one has to reconstruct the locomotor
behaviour of the last common ancestor of
humans and their closest living relatives, the chimpanzees.
Chimpanzees and gorillas adopt a peculiar
mode of locomotion when travelling on the
ground, knuckle-walking (KW). This article evaluates
the evidence for and against the hypothesis
that humans have descended from a KW ancestor.
The conflicting nature of this evidence does
not allow firm conclusions, but future avenues of
research are proposed.
HYPOTHESES
Two sets of hypotheses named food-material-properties (HFMP) and heterochrony (HHET) hypotheses are tested.
HFMP0: Predicts no consistent differences in the patterns and/or intensities of morphological integration between species whose faces experience significantly different biomechanical loads.
HFMP1: Predicts that species relying on selectively important but mechanically resistant foods will have more strongly morphologically integrated faces than species lacking such adaptations.
HFMP2: Predicts the opposite of HFMP1.
HHET0: Predicts no consistent differences in facial integration between the sexes.
HHET1: Predicts that males in dimorphic species will display higher levels of facial integration than conspecific females.
HHET2: Predicts the opposite of HHET1.
BACKGROUND TO HYPOTHESES
HFMP1 expects that facial morphologies which compromise feeding performance and thus have a negative impact on fitness will be selected against resulting in the spread of a functionally advantageous pattern in the population, and by extension in an increase in integration intensity. Such adaptation could also affect the number of functionally-linked elements, since when bite force increases more regions will be subjected to high magnitude strain (Hylander, 1977). The premise of HFMP1 is justified by: 1) numerous studies suggesting that the face, particularly its oral and zygomatic subunits, is the module contributing most extensively to cranial integration in primates (e.g., Marroig and Cheverud, 2001; Ackermann, 2005); 2) reports indicating that groups of mice and primates fed artificially soft diets during development exhibit increased morphological variability and decreased dentognathic integration relative to groups fed harder diets (Beecher and Corruccini, 1981; Beecher et al., 1983; Corruccini and Beecher, 1984).
HFMP2 represents an extrapolation of the Wood-and-Lieberman-2001 hypothesis, which postulates that skeletal structures subject to high or frequent magnitudes of masticatory strain would be more variable within species than those subjected to lower strain magnitudes. One might extrapolate from this hypothesis that if epigenetic stimuli increase variation, that process might also decrease covariance among traits. The hypotheses expecting integration to be sexually dimorphic follow logically from the observations that the face does not terminate its growth until early adulthood (Enlow and Hans, 1996), while growth spurts are sex-dependent (Leigh, 1992). An expectation of HHET1 would further be that integration increa
sutures reflect their functional environment (Rafferty and Herring, 1999). Craniofacial sutures can be viewed weak bone “growth” sites characterized by very different material
properties than the surrounding rigid skull bones; thence they must be shielded from unduly high stresses so as not to disrupt vital growth processes and skeletal functions.
Thus, it is hypothesized that the placement of craniofacial sutures should maximize their growth potentials yet minimize their negative biomechanical impacts, especially in areas
under high stress during dietary activities, such as the midface. Specifically, for any given suture, it is hypothesized that suture position would be different in skulls of different form
and/or adapted to different dietary ecology.
In this pilot study, we investigated the position of the Maxillo-Zygomatic suture (MZS) and the covariance patterns between zygomatic bone 3D sutural and geometric landmarks in a sample including Old World Monkeys (OWMs) and New World Monkeys (NWMs) with the aim to identify phylogenetic (including allometric) effects and distinctions among dietary groups. Further, we studied the association of the zygomatic bone with maxillary and premaxillary traits and neurocranial traits.