Coordinated transformations of the labyrinth and occiput during the dinosaur-bird transition.

October 20, 2026| Source: Proceedings of the National Academy of Sciences of the United States of America

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.

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Extensive glacier loss in the coterminous United States.

Glaciers populate the mountain ranges of the western conterminous United States and despite their importance to alpine hydrology, their area and volume change have never been comprehensively evaluated. Our study shows that since the mid-twentieth century about one-quarter of the glaciers have disappeared and the overall area and volume are reduced by one-third. The pattern of glacier shrinkage suggests most glaciers in the conterminous United States are largely maintained by local topographic in

Physical/TechOctober 20, 2026

Reaction-based cryo-EM resolves the continuous conformational spectrum of CTP synthase catalysis.

Capturing enzymes under native turnover conditions remains a grand challenge in structural biology. Here, we develop a reaction-based cryo-electron microscopy (cryo-EM) strategy that directly samples Drosophila melanogaster cytidine triphosphate synthase (CTPS) from actively catalyzing mixtures containing only natural substrates and allosteric effectors. By integrating reaction-based sampling with three-dimensional variability analysis, we resolve a continuous conformational spectrum of CTPS dur

Physical/TechOctober 20, 2026

GTP orchestrates CTP synthase via an allosteric effector-cycling mechanism.

Cytidine triphosphate (CTP), a fundamental building block of RNA, plays vital roles in diverse biological processes. CTP synthase (CTPS) is the only known enzyme for de novo synthesis of CTP. Efficient CTPS catalysis requires guanosine triphosphate (GTP) in a dose-dependent, nonconsumptive manner; however, the precise mechanism by which GTP drives CTP formation remains unclear. Here, we integrate a series of cryo-EM structures of Drosophila melanogaster CTPS captured from actively catalyzing sam

Physical/TechOctober 20, 2026

Antiferromagnetism and tightly bound Cooper pairs induced by kinetic frustration.

Antiferromagnetism and superconductivity are often viewed as competing orders in correlated electron systems. Here, we demonstrate that kinetic frustration in hole motion facilitates their coexistence within the square-lattice repulsive Hubbard model. Combining exact analytical solutions on tailored geometries with large-scale numerical simulations, we reveal a robust pairing mechanism: Holes on opposite sublattices behave as if they carry opposite effective charges due to spin singlet formation

Physical/TechOctober 20, 2026

Heterochronicity shapes brain network formation.

Brain network formation unfolds on a nonuniform developmental timetable, with different cortical regions generating connections at different developmental phases. Generative network models (GNMs) aim to uncover the principles underpinning the organization of connectomes by creating synthetic networks according to simple computational rules. These models capture the connectome's topology, operationalized here as the cumulative distributions of network metrics (e.g., modularity, small-worldness, r