Figure 1.
Phylogeny used for data mapping.
The composite theropod evolutionary tree used in this study was compiled for non-avian coelurosaurs and for birds from [47], [57], [58], [98], [99], [100] with outgroups from [101]. The names and numbers of the nodes along the theropod lineage between Theropoda and Phasianidae refer to those used in the text.
Figure 2.
Hypothetical vertebral morphologies associated with ‘high’ and ‘low’ joint stiffness properties and the positions of the soft tissues of interest.
Hypothetical models of vertebral morphologies (in lateral and anterior view) that are associated with, A, ‘high’, and, B, ‘low’ intervertebral joint stiffness (after [33]). The position of the ‘vertebral disc’ as well as the interspinalis and intertransversarius ligaments are marked.
Figure 3.
Vertebral parameters measured to reconstruct intervertebral joint stiffness.
Eight biomechanically-informative measurements taken from caudal vertebrae to reconstruct intervertebral joint stiffnesses (Caudal from oviraptorosaurid Citipati osmolskae (MPC 100/978)).
Figure 4.
PCA results: vertebral parameter loadings for PCs 1–3.
PCAs of complete, theropod-only and non-avian theropod-only datasets - vertebral parameter loadings for PCs 1–3. A, complete dataset. For PC1, neural spine height, chevron depth, and vertebral width explained relatively large portions of the variance. B, theropod-only (outgroups excluded) dataset. For PC1, neural spine height and vertebral width explained large portions of the variance. C, non-avian theropod (no outgroups and Avialae/Aves) dataset. For PC1, neural spine height and vertebral width explained the largest portions of the variance.
Table 1.
Percentage variance explained by the principal components for the complete dataset.
Table 2.
Percentage variance explained by the principal components for the theropod dataset.
Table 3.
Percentage variance explained by the principal components for the non-avian theropod dataset.
Figure 5.
Size-normalised tail length and caudal count nodal values reconstructed for amniotes.
Size-normalised amniote nodal values (See Fig. 1; also Materials and Methods): A, tail length, and B, caudal count. Nodes 5–11 are non-avian theropods whereas nodes 12 onwards are birds. Mapping results under EBL and SBL branch length assumptions are labelled as “EBL” and “SBL” respectively. C, tail length and caudal count appear to be proportional (EBL data: y = 0.1233x+0.2553, R2 = 0.9697, r = 0.985 which is significant at the 0.01 level (p (2-tailed) = 0.000); SBL data: y = 0.1217x+0.4225, R2 = 0.9789, r = 0.989 which is significant at the 0.01 level (p (2-tailed) = 0.000)). Node numbers (1–21) are marked next to each EBL and SBL data point.
Figure 6.
Size-normalised height and depth nodal values reconstructed for amniotes.
Size-normalised amniote nodal values: A, neural spine height, B, transverse process height, C, centrum height, and D, chevron depth. The proximal, middle and distal regions of the tail are abbreviated as: “prox”, “mid” and “dist”. See Figure 5 for more information.
Figure 7.
Size-normalised length and width nodal values reconstructed for amniotes.
Size-normalised amniote nodal values: A, neural spine length, B, transverse process length, C, centrum length, and D, vertebral width. See Figures 5 and 6 for more information.
Figure 8.
Qualitative character mapping results for the complete amniote dataset.
Qualitative tail characteristics reconstructed at amniote nodes using a matrix of data compiled from the entire dataset, and first-hand observations of specimens.
Figure 9.
Pictorial renderings of hypothetical proximal, middle and distal caudal vertebrae reconstructed at theropod nodes.
Figure 9. Hypothetical pictorial renderings of proximal, middle and distal caudal vertebrae reconstructed at the nodes: A, Theropoda (node 5), B, Avialae (node 12), C, Pygostylia (node 15), and D, Neornithes (node 19).