Data from: Phylogenetic variation in hind-limb bone scaling of flightless theropods

The robusticity of the weight-bearing limbs of large terrestrial animals is expected to increase at a more rapid rate than in their smaller relatives. This scaling has been hypothesized to allow large species to maintain stresses in the limb bones that are similar to those seen in smaller ones. Curvilinear scaling has previously been found in mammals and nonavian theropods but has not been demonstrated in birds. In this study, polynomial regressions of leg-bone length and circumference in terrestrial flightless birds were carried out to test for a relationship similar to that seen in nonavian theropods. Flightless birds exhibit curvilinear scaling, with the femora of large taxa becoming thicker relative to length at a greater rate than in smaller taxa. Evidence was found for nonlinear scaling in the leg bones of nonavian theropods. However, unlike in avians, there is also phylogenetic variation between taxonomic groups, with tyrannosaur leg bones in particular scaling differently than other groups. Phylogenetically corrected quadratic regressions and separate analyses of taxonomic groupings found little phylogenetic variation in flightless birds. It is suggested here that the nonlinear scaling seen in avian femora is due to the need to maintain the position of the knee under a more anterior center of mass, thereby restricting femoral length. The femur of nonavian theropods is not so constrained, with greater variability of the linear scaling relationships between clades. Phylogenetic variation in limb-bone scaling may broaden the errors for mass-predictive scaling equations based on limb-bone measurements of nonavian theropods.

Usage Notes
Appendix S1Femur and tibia lengths and circumferences from flightless birds and non-avian theropods, including references for non-avian theropod data.Supplementary FiguresPhotographs of avian leg bones with key features labelled (Fig. S1A and S1B), and time scaled strict consenus trees of flightless birds (Fig. S2) and non-avian theropods (Fig. S3) included in regression analyses.Appendix S2Matrix representation parsimony codings for flightless avians and non-avian theropods with list of source phylogenies and first and last appearance dates of taxa with data sources listed.

大型陆生动物的承重肢粗壮度预计将以高于其小型近亲的速率增长。这一异速生长（scaling）假说认为，大型物种可维持其肢骨所受应力与小型物种相近的水平。此前在哺乳类与非鸟类兽脚类（nonavian theropods）中已观测到曲线异速生长现象，但在鸟类中尚未得到验证。
本研究针对陆生无翼鸟类的腿骨长度与周长开展多项式回归分析，以检验是否存在与非鸟类兽脚类相似的关联模式。
无翼鸟类呈现曲线异速生长特征：大型类群的股骨相较于长度的增厚速率高于小型类群。研究在非鸟类兽脚类的腿骨中发现了非线性异速生长的证据。不过与鸟类不同的是，非鸟类兽脚类的不同类群间存在系统发育变异，其中暴龙类（tyrannosaur）的腿骨异速生长模式与其他类群差异尤为显著。经系统发育校正的二次回归以及针对类群分组的独立分析显示，无翼鸟类几乎不存在系统发育变异。
本研究提出，鸟类股骨的非线性异速生长现象，源于需要将膝关节维持在更靠前的质心位置，进而限制了股骨长度。而非鸟类兽脚类的股骨并无此类约束，其不同演化支的线性异速生长关系具有更高的变异性。肢骨异速生长的系统发育变异，可能会增大基于非鸟类兽脚类肢骨测量数据构建的质量预测异速生长方程的误差。

使用说明
附录S1：收录无翼鸟类与非鸟类兽脚类的股骨、胫骨长度及周长数据，并附非鸟类兽脚类数据的参考文献。
补充图：包含标注了关键特征的鸟类腿骨照片（图S1A、S1B），以及纳入回归分析的无翼鸟类（图S2）与非鸟类兽脚类（图S3）的时间标度严格合意树。
附录S2：收录无翼鸟类与非鸟类兽脚类的矩阵表示简约编码表，附系统发育来源列表，以及带有数据来源的类群的首现与末现日期。