Principal coordinates analysis (PCoA) is a statistical ordination technique commonly applied to morphology-based cladistic matrices to study macroevolutionary patterns, morphospace occupation, and disparity. However, PCoA-based morphospaces are dissociated from the original data; therefore, whether such morphospaces accurately reflect body-plan disparity or extrinsic factors, such as body size, remains uncertain. We collated nine character–taxon matrices of dinosaurs together with body-mass estimates for all taxa and tested for relationships between body size and both the principal axis of variation (i.e., PCo1) and the entire set of PCo scores. The possible effects of body size on macroevolutionary hypotheses derived from ordinated matrices were tested by reevaluating evidence for the accelerated accumulation of avian-type traits indicated by a strong directional shift in PCo1 scores in hypothetical ancestors of modern birds. Body mass significantly accounted for, on average, approximately 50% and 16% of the phylogenetically corrected variance in PCo1 and all PCo scores, respectively. Along the avian stem lineage, approximately 30% of the morphological variation is attributed to the reconstructed body masses of each ancestor. When the effects of body size are adjusted, the period of accelerated trait accumulation is replaced by a more gradual, additive process. Our results indicate that even at low proportions of variance, body size can noticeably affect macroevolutionary hypotheses generated from ordinated morphospaces. Future studies should thoroughly explore the nature of their character data in association with PCoA-based morphospaces and use a residual/covariate approach to account for potential correlations with body size.

中文翻译：

---

体型与离散特征形态代理相关

主坐标分析 (PCoA) 是一种统计排序技术，通常应用于基于形态学的分支矩阵，以研究宏观进化模式、形态空间占用和视差。然而，基于 PCoA 的形态空间与原始数据分离；因此，这些形态空间是否准确地反映了身体计划差异或外部因素，如身体大小，仍然不确定。我们整理了恐龙的九个特征分类单元矩阵以及所有分类单元的体重估计值，并测试了体型与变异主轴（即 PCo1）和整个 PCo 分数之间的关系。通过重新评估禽类特征加速积累的证据，测试了体型大小对源自纵坐标矩阵的宏观进化假设的可能影响，这表明现代鸟类的假设祖先中 PCo1 分数的强烈方向变化表明。平均而言，体重显着分别占 PCo1 和所有 PCo 分数的系统发育校正方差的约 50% 和 16%。沿着鸟类的茎谱系，大约 30% 的形态变异归因于每个祖先的重建体重。当调整体型的影响时，加速性状积累的时期被一个更渐进的、附加的过程所取代。我们的结果表明，即使在低比例的方差下，体型可以显着影响由协调形态空间产生的宏观进化假设。未来的研究应彻底探索其特征数据与基于 PCoA 的形态空间相关的性质，并使用残差/协变量方法来解释与体型的潜在相关性。