Artificial neural networks and geometric morphometric methods as a means for classification: A case-study using teeth from Carcharhinus sp. (Carcharhinidae).

Over the past few decades, geometric morphometric methods have become increasingly popular and powerful tools to describe morphological data while over the same period artificial neural networks have had a similar rise in the classification of specimens to preconceived groups. However, there has been little research into how well these two systems operate together, particularly in comparison to preexisting techniques. In this study, geometric morphometric data and multilayer perceptrons, a style of artificial neural network, were used to classify shark teeth from the genus Carcharhinus to species. Three datasets of varying size and species differences were used. We compared the performance of this combination with geometric morphometric data in a linear discriminate function analysis, linear measurements in a linear discriminate function analysis, and a preexisting methodology from the literature that incorporates linear measurements and a two-layered discriminate function analysis. Across datasets, geometric morphometric data in a multilayer perceptron tended to yield modest accuracies but accuracies that varied less across species whereas other methods were able to achieve higher accuracies in some species at the expense of lower accuracies in others. Further, the performance of the two-layered discriminate function analysis illustrates that constraining what material is classified can increase the accuracy of a method. Based on this tradeoff, the best methodology will then depend on the scope of the study and the amount of material available. J. Morphol. 278:131-141, 2017. ©© 2016 Wiley Periodicals,Inc.

The utility of cranial ontogeny for phylogenetic inference: a case study in crocodylians using geometric morphometrics.

The degree to which the ontogeny of organisms could facilitate our understanding of phylogenetic relationships has long been a subject of contention in evolutionary biology. The famed notion that 'ontogeny recapitulates phylogeny' has been largely discredited, but there remains an expectation that closely related organisms undergo similar morphological transformations throughout ontogeny. To test this assumption, we used three-dimensional geometric morphometric methods to characterize the cranial morphology of 10 extant crocodylian species and construct allometric trajectories that model the post-natal ontogenetic shape changes. Using time-calibrated molecular and morphological trees, we employed a suite of comparative phylogenetic methods to assess the extent of phylogenetic signal in these trajectories. All analyses largely demonstrated a lack of significant phylogenetic signal, indicating that ontogenetic shape changes contain little phylogenetic information. Notably, some Mantel tests yielded marginally significant results when analysed with the morphological tree, which suggest that the underlying signal in these trajectories is correlated with similarities in the adult cranial morphology. However, despite these instances, all other analyses, including more powerful tests for phylogenetic signal, recovered statistical and visual evidence against the assumption that similarities in ontogenetic shape changes are commensurate with phylogenetic relatedness and thus bring into question the efficacy of using allometric trajectories for phylogenetic inference.

Aging and the shape of the mandible.

BACKGROUND: The clinical observation has been made that the shape of the mandible changes with age in certain individuals. Because the shape and size of the mandible are so important to the human perception of youth, this observation was subjected to a pilot study. METHODS: Longitudinal data available at the Bolton Brush Growth Study were evaluated. Only dentate individuals were included in the study. Serial frontal radiographs were analyzed from the same individual taken during youth and maturity for 16 individuals, eight female subjects and eight male subjects (n = 16). The mean age for youth was 16.2 years for female and male subjects. The mean age at maturity was 56.1 years for female subjects and 56.4 years for male subjects. Tracings were made of the mandibular border for each individual, at youth and at maturity. The only reliable way to analyze shape is the modern technique of geometric morphometric analysis, which was therefore used in this study. Other techniques, such as angular values and two-dimensional linear measurements, were dismissed because they have been shown to be unreliable for evaluating shape. RESULTS: There was a statistically significant difference in shape for both male subjects and female subjects that occurred with age (p = 0.02 for female subjects and p = 0.001 for male subjects). The mandible continued to grow: the shape changed because some areas continued to grow faster than other areas. This is in accordance with the principle of differential growth of the facial skeleton. CONCLUSIONS: It is important for the cosmetic surgeon to evaluate the lower face before surgery and to understand that both bone and soft tissue can play a role in the appearance of the lower face in older individuals. A small lower face is highly attractive and conveys the impression of youth, and any soft-tissue procedure that can create the illusion of a diminutive lower face will improve the cosmetic result of the face lift procedure.

A geometric morphometric assessment of change in midline brain structural shape following a first episode of schizophrenia.

BACKGROUND: Previous reports indicate that brain structural abnormalities may be progressive in some patients with schizophrenia. Our study was designed to determine deviations in the shape of midline brain structures at the time of onset of symptoms of schizophrenia and 3-5 years later. METHODS: Eleven landmarks were located on the midsagittal magnetic resonance imagery brain scans of 55 patients with schizophrenia and 22 nonpsychiatric control individuals. Geometric morphometric methods were used for the extraction of shape variables from landmark coordinates. Permutation tests were used to test the effects of gender, diagnosis, time elapsed since illness onset, and age on brain shape. RESULTS: The diagnosis-by-time interaction and the effect of gender were significantly different from zero (p<.027 and p <.039, respectively). The effect of time was significant in patients (p <.002), but not in control subjects. Some anatomical abnormalities in mean patient brain morphology seem to be present both at the time of diagnosis and at follow-up. These are similar to anomalies reported by previous geometric morphometrics studies. CONCLUSIONS: Some previously identified brain abnormalities are detectable at the time of first hospitalization. The rapid change in midline brain morphology in patients with schizophrenia during the subsequent 3-5 years is consistent with either a neurodegenerative disease process or an effect of treatment with psychiatric drugs. There is a sexual dimorphism in brain morphology that might be reduced by schizophrenia.

Comparing frontal cranial profiles in archaic and modern homo by morphometric analysis.

Archaic and modern human frontal bones are known to be quite distinct externally, by both conventional visual and metric evaluation. Internally this area of the skull has been considerably less well-studied. Here we present results from a comparison of interior, as well as exterior, frontal bone profiles from CT scans of five mid-Pleistocene and Neanderthal crania and 16 modern humans. Analysis was by a new morphometric method, Procrustes analysis of semi-landmarks, that permits the statistical comparison of curves between landmarks. As expected, we found substantial external differences between archaic and modern samples, differences that are mainly confined to the region around the brow ridge. However, in the inner median-sagittal profile, the shape remained remarkably stable over all 21 specimens. This implies that no significant alteration in this region has taken place over a period of a half-million years or more of evolution, even as considerable external change occurred within the hominid clade spanning several species. This confirms that the forms of the inner and outer aspects of the human frontal bone are determined by entirely independent factors, and further indicates unexpected stability in anterior brain morphology over the period during which modern human cognitive capacities emerged. Anat Rec (New Anat): 257:217-224, 1999.