The phylogenetic distribution of caudal pneumaticity in sauropods and other dinosaurs is complex.

<p>Boxes represent proximal, middle, and distal caudal vertebrae, arbitrarily defined for sauropods as caudals 1–10, 11–20, and 21 on, respectively; blue boxes indicate that pneumaticity is present in that part of the tail. Pneumaticity data for theropods come from Benson <i>et al</i> <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078213#pone.0078213-Benson1" target="_blank">[15]</a>—note that although Theropoda is collapsed to a single node in this figure, caudal pneumaticity is not primitive for the clade, but evolved independently several times in both non-avian theropods and birds <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078213#pone.0078213-OConnor1" target="_blank">[6]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078213#pone.0078213-Benson1" target="_blank">[15]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078213#pone.0078213-OConnor4" target="_blank">[29]</a>. Data from sauropods come from the sources listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078213#pone-0078213-t001" target="_blank">Table 1</a>. The figure also shows the phylogenetic framework we use in this paper. The phylogenetic framework is drawn from Whitlock <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078213#pone.0078213-Whitlock1" target="_blank">[44]</a> for diplodocoids, Mannion <i>et al</i> <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078213#pone.0078213-Mannion1" target="_blank">[30]</a> for basal macronarians and <i>Xianshanosaurus</i>, Calvo <i>et al</i> <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078213#pone.0078213-Calvo1" target="_blank">[96]</a> for most titanosaurs, and Campos <i>et al</i> <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0078213#pone.0078213-Campos1" target="_blank">[93]</a> for <i>Trigonosaurus</i>. Basal sauropodomorphs are a grade, not a clade, but they are listed together here for convenience since they all lack caudal pneumaticity.