BackgroundThe 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.MethodsIn 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.

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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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 23-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 nonmetric 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 sign...

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. Key Concepts A hypothesis links observed patterns to the factors proposed to have caused it. Scientists do not attempt to prove that a hypothesis is true. Hypothesis testing guides scientific research by narrowing down possible explanations for a phenomenon, using the principle of elimination of alternative scenarios. Statistical tests assess the probability that a hypothesis is true or false. It is important for hypotheses to specify testable predictions. Several hypotheses have been proposed to explain the origin of modern humans. Hypotheses explaining modern human origins each make several predictions, some of which can be readily tested using paleontological and genetic data.