Common Functional Correlates of Head-Strike Behavior in the Pachycephalosaur Stegoceras validum (Ornithischia, Dinosauria) and Combative Artiodactyls

BACKGROUND: Pachycephalosaurs were bipedal herbivorous dinosaurs with bony domes on their heads, suggestive of head-butting as seen in bighorn sheep and musk oxen. Previous biomechanical studies indicate potential for pachycephalosaur head-butting, but bone histology appears to contradict the behavior in young and old individuals. Comparing pachycephalosaurs with fighting artiodactyls tests for common correlates of head-butting in their cranial structure and mechanics. METHODS/PRINCIPAL FINDINGS: Computed tomographic (CT) scans and physical sectioning revealed internal cranial structure of ten artiodactyls and pachycephalosaurs Stegoceras validum and Prenocephale prenes. Finite element analyses (FEA), incorporating bone and keratin tissue types, determined cranial stress and strain from simulated head impacts. Recursive partition analysis quantified strengths of correlation between functional morphology and actual or hypothesized behavior. Strong head-strike correlates include a dome-like cephalic morphology, neurovascular canals exiting onto the cranium surface, large neck muscle attachments, and dense cortical bone above a sparse cancellous layer in line with the force of impact. The head-butting duiker Cephalophus leucogaster is the closest morphological analog to Stegoceras, with a smaller yet similarly rounded dome. Crania of the duiker, pachycephalosaurs, and bighorn sheep Ovis canadensis share stratification of thick cortical and cancellous layers. Stegoceras, Cephalophus, and musk ox crania experience lower stress and higher safety factors for a given impact force than giraffe, pronghorn, or the non-combative llama. CONCLUSIONS/SIGNIFICANCE: Anatomy, biomechanics, and statistical correlation suggest that some pachycephalosaurs were as competent at head-to-head impacts as extant analogs displaying such combat. Large-scale comparisons and recursive partitioning can greatly refine inference of behavioral capability for fossil animals

Data from: Incomplete specimens in geometric morphometric analyses

1.The analysis of morphological diversity frequently relies on the use of multivariate methods for characterizing biological shape. However, many of these methods are intolerant of missing data, which can limit the use of rare taxa and hinder the study of broad patterns of ecological diversity and morphological evolution. This study applied a mutli-dataset approach to compare variation in missing data estimation and its effect on geometric morphometric analysis across taxonomically-variable groups, landmark position and sample sizes. 2.Missing morphometric landmark data was simulated from five real, complete datasets, including modern fish, primates and extinct theropod dinosaurs. Missing landmarks were then estimated using several standard approaches and a geometric-morphometric-specific method. The accuracy of missing data estimation was determined for each estimation method, landmark position, and morphological dataset. Procrustes superimposition was used to compare the eigenvectors and principal component scores of a geometric morphometric analysis of the original landmark data, to datasets with A) missing values estimated, or B) simulated incomplete specimens excluded, for varying levels of specimens incompleteness and sample sizes. 3.Standard estimation techniques were more reliable estimators and had lower impacts on morphometric analysis compared to a geometric-morphometric-specific estimator. For most datasets and estimation techniques, estimating missing data produced a better fit to the structure of the original data than exclusion of incomplete specimens, and this was maintained even at considerably reduced sample sizes. The impact of missing data on geometric morphometric analysis was disproportionately affected by the most fragmentary specimens. 4.Missing data estimation was influenced by variability of specific anatomical features, and may be improved by a better understanding of shape variation present in a dataset. Our results suggest that the inclusion of incomplete specimens through the use of effective missing data estimators better reflects the patterns of shape variation within a dataset than using only complete specimens, however the effectiveness of missing data estimation can be maximized by excluding only the most incomplete specimens. It is advised that missing data estimators be evaluated for each dataset and landmark independently, as the effectiveness of estimators can vary strongly and unpredictably between different taxa and structures

Data from: A major shift in diversification rate helps explain macroevolutionary patterns in primate species diversity

Primates represent one of the most species rich, wide ranging and ecologically diverse clades of mammals. What major macroevolutionary factors have driven their diversification and contributed to the modern distribution of primate species remains widely debated. We employed phylogenetic comparative methods to examine the role of clade age and evolutionary rate heterogeneity in the modern distribution of species diversity of Primates. Primate diversification has accelerated since its origin, with decreased extinction leading to a shift to even higher evolutionary rates in the most species rich family (Cercopithecidae). Older primate clades tended to be more diverse, however a shift in evolutionary rate was necessary to adequately explain the imbalance in species diversity. Species richness was also poorly explained by geographic distribution, especially once clade age and evolutionary rate shifts were accounted for, and may relate instead to other ecological factors. The global distribution of primate species diversity appears to have been strongly impacted by heterogeneity in evolutionary rates

Data from: Adaptive landscape and functional diversity of Neotropical cichlids: implications for the ecology and evolution of Cichlinae (Cichlidae; Cichliformes)

Morphological, lineage and ecological diversity can vary substantially even among closely related lineages. Factors that influence morphological diversification, especially in functionally relevant traits, can help to explain the modern distribution of disparity across phylogenies and communities. Multivariate axes of feeding functional morphology from 75 species of Neotropical cichlid and a stepwise-AIC algorithm were used to estimate the adaptive landscape of functional morphospace in Cichlinae. Adaptive landscape complexity and convergence, as well as the functional diversity of Cichlinae, were compared with expectations under null evolutionary models. Neotropical cichlid feeding function varied primarily between traits associated with ram feeding vs. suction feeding/biting and secondarily with oral jaw muscle size and pharyngeal crushing capacity. The number of changes in selective regimes and the amount of convergence between lineages was higher than expected under a null model of evolution, but convergence was not higher than expected under a similarly complex adaptive landscape. Functional disparity was compatible with an adaptive landscape model, whereas the distribution of evolutionary change through morphospace corresponded with a process of evolution towards a single adaptive peak. The continentally distributed Neotropical cichlids have evolved relatively rapidly towards a number of adaptive peaks in functional trait space. Selection in Cichlinae functional morphospace is more complex than expected under null evolutionary models. The complexity of selective constraints in feeding morphology has likely been a significant contributor to the diversity of feeding ecology in this clade

Guianacara dacrya, a new species from the rio Branco and Essequibo River drainages of the Guiana Shield (Perciformes: Cichlidae)

A new species of Guianacara is described from tributaries of the Essequibo River and the rio Branco in Guyana and northern Brazil. Guianacara dacrya, new species, can be diagnosed from all congeners by the possession of a unique infraorbital stripe and by the shape of the lateral margin of the lower pharyngeal jaw tooth plate. Guianacara dacrya can be further distinguished from G. geayi, G. owroewefi, G. sphenozona and G. stergiosi by the possession of a thin midlateral bar, from G. cuyunii by the possession of dusky branchiostegal membranes and from G. oelemariensis by the possession of two supraneurals. This species differs from most congeners by the presence of white spots on the spiny portion of the dorsal fin, the placement of the midlateral spot, the presence of filaments on the dorsal, anal and in rare cases the caudal-fin and from at least the Venezuelan species by several morphometric variables. Guianacara dacrya is known from the Essequibo, Takutu and Ireng River basins of Guyana and possibly from the rio Uraricoera in the rio Branco basin in Brazil. A key to the species is provided

Table 2 Guianacara dacrya landmarks

Sixteen landmarks from 73 specimens, from the description of Guianacara dacrya (see Arbour and Lopez-Fernandez, 2011, Neotropical Ichthyology 9(1):87-96.

Functional morphology of 75 species of Cichlinae

Table includes mean values for functional morphology and body size from 75 species of Neotropical cichlids from both South and Central America and including all tribes of Cichlinae

Data from: Selection towards different adaptive optima drove the early diversification of locomotor phenotypes in the radiation of Neotropical geophagine cichlids

Background: Simpson envisaged a conceptual model of adaptive radiation in which lineages diversify into "adaptive zones" within a broad adaptive landscape. However only a handful of studies have actually investigated the adaptive landscape and its implication for our interpretation of the underlying mechanisms of phenotypic evolution. In fishes the evolution of locomotor phenotypes may represent an important dimension of ecomorphological diversification during an adaptive radiation given its implications for feeding and habitat use. Neotropical geophagine cichlids represent a newly identified adaptive radiation and provide a useful system for studying patterns of locomotor diversification and the implications of selective constraints on phenotypic divergence in general. Results: We use multivariate ordination models of phenotypic evolution and posterior predictive approaches to investigate the adaptive landscape and test for evidence of early diversification of locomotor phenotypes in Geophagini. The evolution of locomotor phenotypes was characterized by divergent selection towards two distinct adaptive peaks and the early divergence of modern morphological disparity. Evolutionary models and posterior predictive approaches favoured constant-rate divergent selection over decreasing rates of phenotypic evolution as the underlying process driving the early divergence of locomotor phenotypes. Conclusions: The influence of multiple adaptive peaks on the divergence of locomotor attributes in Geophagini is compatible with the expectations of an ecologically-driven adaptive radiation. This study confirms that the diversification of locomotor morphology represents an important dimension of phenotypic evolution in the geophagine adaptive radiation. It also suggests that the commonly observed early burst of phenotypic evolution during adaptive radiations is best explained by a model that incorporates divergent selection deep in the phylogeny