DOI: 10.5061/dryad.ft3ps
title: Data from: Comparative analysis of vestibular ecomorphology in birds

description: The bony labyrinth of vertebrates houses the semicircular canals. These
 sense rotational accelerations of the head and play an essential role in
 gaze stabilisation during locomotion. The sizes and shapes of the
 semicircular canals have hypothesised relationships to agility and
 locomotory modes in many groups, including birds, and a burgeoning
 palaeontological literature seeks to make ecological interpretations from
 the morphology of the labyrinth in extinct species. Rigorous tests of
 form–function relationships for the vestibular system are required to
 support these interpretations. We test the hypothesis that the lengths,
 streamlines and angles between the semicircular canals are related to body
 size, wing kinematics and flying style in birds. To do this, we applied
 geometric morphometrics and multivariate phylogenetic comparative methods
 to a dataset of 64 three-dimensional reconstructions of the endosseous
 labyrinth obtained using micro-computed tomography scanning of bird
 crania. A strong relationship between centroid size of the semicircular
 canals and body size indicates that larger birds have longer semicircular
 canals compared with their evolutionary relatives. Wing kinematics related
 to manoeuvrability (and quantified using the brachial index) explain a
 small additional portion of the variance in labyrinth size. We also find
 strong evidence for allometric shape change in the semicircular canals of
 birds, indicating that major aspects of the shape of the avian labyrinth
 are determined by spatial constraints. The avian braincase accommodates a
 large brain, a large eye and large semicircular canals compared with other
 tetrapods. Negative allometry of these structures means that the
 restriction of space within the braincase is intense in small birds. This
 may explain our observation that the angles between planes of the
 semicircular canals of birds deviate more strongly from orthogonality than
 those of mammals, and especially from agile, gliding and flying mammals.
 Furthermore, we find little support for relationships between labyrinth
 shape and flying style or wing kinematics. Overall, our results suggest
 that the topological problem of fitting long semicircular canals into a
 spatially constrained braincase is more important in determining the shape
 of the avian labyrinth than the specifics of locomotory style or agility.
 Our results tentatively indicate a link between visual acuity and
 proportional size of the labyrinth among birds. This suggests that the
 large labyrinths of birds compared with other tetrapods may result from
 their generally high visual acuities, and not directly from their ability
 to fly. The endosseous labyrinths of extinct birds and their close
 dinosaurian relatives may allow broad inferences about flight or vision,
 but so far provide few specific insights into detailed aspects of
 locomotion.
description: PC
 moviesZIPped folder containing
 .mov files showing the shape deformations along principal component axes
 (PC1-PC8) for our analyses at x1 magnification and x2 magnification of the
 observed magnitudes of shape change.3D labyrinth
 modelsZIPped folder containing
 3D virtual models in .ply format of the endosseous labyrinth and
 semicircular canals. These models, and the parent microCT data are also
 housed at Morphosource
 (http://morphosource.org/Detail/ProjectDetail/Show/project_id/377)Landmarks and semilandmarksLandmark and semi landmark data used in our analyses. Abbreviations: ASC, anterior semicircular canal; PSC, posterior semicircular canal; LSC, lateral semicircular canal.Landmarks.txtQuantitative data tableFlight mode classification, body mass, brachial index (BI), inter-canal plane angles (in radians), and PC scores (for PC1-PC65) used in our analyses.BirdTaxonData.csvPhylogenetic treesSet of 100 phylogenetic trees from Jetz et al (2008; Ericson backbone) used in our analyses)Trees.treSupplementary text figures tablesFig. S1. Summary of 2B-PLS results comparing multivariate flight style to PC shape axes for endosseous labyrinth morphology including outliers and including all shape axes. Fig. S2. Summary of 2B-PLS results comparing multivariate flight style to PC shape axes for endosseous labyrinth morphology including outliers and including all shape axes except PC1. Fig. S3. Summary of 2B-PLS results comparing multivariate flight style to PC shape axes for endosseous labyrinth morphology including outliers and including all shape axes, excluding four outlier taxa. Table S1. Results of regressions of labyrinth inter-canal angles on body mass and BI. Table S2. Results of regressions of positivised deviations of labyrinth inter-canal angles from 90 ° on body mass and BI. Table S3. Results of regressions of summed positivised devia- tions of labyrinth inter-canal angles from 90 ° on body mass and BI. Table S4. Regression model comparison results for principal component PC4. Table S5. Regression model comparison results for principal component PC5. Table S6. Regression model comparison results for principal component PC6. Table S7. Regression model comparison results for principal component PC7. Table S8. Regression model comparison results for principal component PC8. Appendix S1. Discussion of flight categories.