Small body size is associated with increased evolutionary lability of wing skeleton proportions in birds.

Birds are represented by 11,000 species and a great variety of body masses. Modular organisation of trait evolution across birds has facilitated simultaneous adaptation of different body regions to divergent ecological requirements. However, the role modularity has played in avian body size evolution, especially small-bodied, rapidly evolving and diverse avian subclades, such as hummingbirds and songbirds, is unknown. Modularity is influenced by the intersection of biomechanical restrictions, adaptation, and developmental controls, making it difficult to uncover the contributions of single factors such as body mass to skeletal organisation. We develop a novel framework to decompose this complexity, assessing factors underlying the modularity of skeletal proportions in fore-limb propelled birds distributed across a range of body masses. We demonstrate that differences in body size across birds triggers a modular reorganisation of flight apparatus proportions consistent with biomechanical expectations. We suggest weakened integration within the wing facilitates radiation in small birds. Our framework is generalisable to other groups and has the capacity to untangle the multi-layered complexity intrinsic to modular evolution.

Subaqueous foraging among carnivorous dinosaurs.

Secondary aquatic adaptations evolved independently more than 30 times from terrestrial vertebrate ancestors1,2. For decades, non-avian dinosaurs were believed to be an exception to this pattern. Only a few species have been hypothesized to be partly or predominantly aquatic3-11. However, these hypotheses remain controversial12,13, largely owing to the difficulty of identifying unambiguous anatomical adaptations for aquatic habits in extinct animals. Here we demonstrate that the relationship between bone density and aquatic ecologies across extant amniotes provides a reliable inference of aquatic habits in extinct species. We use this approach to evaluate the distribution of aquatic adaptations among non-avian dinosaurs. We find strong support for aquatic habits in spinosaurids, associated with a marked increase in bone density, which precedes the evolution of more conspicuous anatomical modifications, a pattern also observed in other aquatic reptiles and mammals14-16. Spinosaurids are revealed to be aquatic specialists with surprising ecological disparity, including subaqueous foraging behaviour in Spinosaurus and Baryonyx, and non-diving habits in Suchomimus. Adaptation to aquatic environments appeared in spinosaurids during the Early Cretaceous, following their divergence from other tetanuran theropods during the Early Jurassic17.

Shine a light: Under-ice light and its ecological implications in a changing Arctic Ocean.

The Arctic marine ecosystem is shaped by the seasonality of the solar cycle, spanning from 24-h light at the sea surface in summer to 24-h darkness in winter. The amount of light available for under-ice ecosystems is the result of different physical and biological processes that affect its path through atmosphere, snow, sea ice and water. In this article, we review the present state of knowledge of the abiotic (clouds, sea ice, snow, suspended matter) and biotic (sea ice algae and phytoplankton) controls on the underwater light field. We focus on how the available light affects the seasonal cycle of primary production (sympagic and pelagic) and discuss the sensitivity of ecosystems to changes in the light field based on model simulations. Lastly, we discuss predicted future changes in under-ice light as a consequence of climate change and their potential ecological implications, with the aim of providing a guide for future research.

Patterns of skeletal integration in birds reveal that adaptation of element shapes enables coordinated evolution between anatomical modules.

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.