Alexander Bjarnason

Evolutionary shape changes of the vertebrate semicircular canals (SCCs) are often ascribed to evolutionary transitions in locomotion, including the origin of flight during the dinosaur–bird transition. However, the potential for transformations of braincase architecture to influence SCC shape independent of sensory-functional adaptation has generally been overlooked. We evaluate the influence of both factors using a large dataset of 146 living and recently extinct crown birds, including taxa representing ~24 independent evolutionary losses of flight, together with Mesozoic stem avialans, nonavialan dinosaurs, and pterosaurs. Among crown birds, evolutionary changes in locomotor capabilities, including the total loss of flight, have only weak effects on SCC shape, contrasting with large effects from changes in braincase geometry. Notably, rotation of the occiput toward a ventral orientation is associated with important changes to SCC shape that match those observed during the dinosaur–bird transition. This suggests that evolutionary transformations of SCC shape during the Mesozoic origin of avian flight resulted from evolutionary changes in the orientation of the craniocervical joint, and not from tuning of SCC sensory function. These findings illuminate the importance of integrated morphological changes to the head-neck system during bird origins and challenge the long-standing assumption that SCC morphology enables confident inferences of the locomotor capabilities of extinct vertebrates.

Birds show tremendous ecological disparity in spite of strong biomechanical constraints imposed by flight. Modular skeletal evolution is generally accepted to have facilitated this, with distinct body regions showing semi-independent evolutionary trajectories. However, this hypothesis has received little scrutiny. We analyse evolutionary modularity and ecomorphology using three-dimensional data from across the entire skeleton in a phylogenetically broad sample of extant birds. We find strongly modular evolution of skeletal element sizes within body regions (head, trunk, forelimb and hindlimb). However, element shapes show substantially less modularity, have stronger relationships to ecology, and provide evidence that ecological adaptation involves coordinated evolution of elements across different body regions. This complicates the straightforward paradigm in which modular evolution facilitated the ecological diversification of birds. Our findings suggest the potential for undetected patterns of morphological evolution in even well-studied groups, and advance the understanding of the interface between evolutionary integration and ecomorphology.

Invasive alien species cause major changes to ecosystem functioning and patterns of biodiversity, and the main factors involved in invasion success remain contested. Using the Mediterranean island of Crete as a case study, we present a framework for analyzing spatial data of alien species distributions, based on environmental predictors, aiming to gain an understanding of their spatial patterns and spread. Mediterranean islands are under strong ecological pressure from invading species due to their restricted size and increased human impact. Four hypotheses of invasibility, the ‘propagule pressure hypothesis’ (H1), ‘biotic resistance hypothesis vs. acceptance hypothesis’ (H2), ‘disturbance-mediated hypothesis’ (H3), and ‘environmental heterogeneity hypothesis’ (H4) were tested. Using data from alien, native, and endemic vascular plant species, the propagule pressure, biotic resistance versus acceptance, disturbance-mediated, and environmental heterogeneity hypotheses were tested with Generalized Additive Modelling (GAM) of 39 models. Based on model selection, the optimal model includes the positive covariates of native species richness, the negative covariates of endemic species richness, and land area. Variance partitioning between the four hypotheses indicated that the biotic resistance versus acceptance hypothesis explained the vast majority of the total variance. These results show that areas of high species richness have greater invasibility and support the acceptance hypothesis and “rich-get-richer” distribution of alien species. The negative correlation between alien and endemic species appears to be predominantly driven by altitude, with fewer alien and more endemic species at greater altitudes, and habitat richness. The negative relationship between alien and endemic species richness provides potential for understanding patterns of endemic and alien species on islands, contributing to more effective conservation strategies.

Pitheciids, one of the major radiations of New World monkeys endemic to South and Central America, are distributed in the Amazon and Orinoco basins, and include Callicebus, Cacajao, Chiropotes, and Pithecia. Molecular phylogenetics strongly support pitheciid monophyly, whereas morphological analyses infer a range of phylogenies including a sister relationship between Aotus and Callicebus. We collected geometric morphometric cranial data from pitheciids and Aotus, and used cranial data for distance‐based phylogenetic analysis and tests of phylogenetic signal. Phylogenetic analyses of pitheciids were repeated with Lagothrix, Callimico, and Saimiri outgroups for Procrustes shape with and without Aotus based on the whole cranium and six anatomical regions. All phylogenetic signal tests were significant, and tree lengths were shortest and had the least morphological change over the phylogeny for Procrustes residuals from the cranial base and palate. The majority of phylogenetic analyses of Procrustes shape for pitheciids without Aotus supported the molecular phylogeny, and with Aotus included the majority inferred an Aotus–Callicebus clade, although three analyses with Callimico as outgroup supported the molecular phylogeny. The morphological similarity of Aotus and Callicebus is likely a mix of plesiomorphy, allometry, and homoplasy, and future phylogenetic inference of living and extinct platyrrhine taxa should consider the impact of these factors alongside outgroup selection and cranial region.