Enlargement of sternum traits facilitated the evolution of powered flight in birds

An enlarged sternum with a prominent keel is a central feature of the flight apparatus of modern birds. However, sterna of near-bird dinosaurs (Pennaraptora) and early avialans are either significantly different from those of living birds or absent altogether, raising questions on how specialized sternal structures evolved in birds and how they are related to function. This remains poorly understood due to the fragmentary nature of the fossil record, and the challenges in inferring form and function from crushed fossils. We employ ancestral character estimations to trace sternal trait acquisition through the bird stem group, and multivariate phylogenetic regressions to analyze relationships between sternum morphology, body mass, and flight capabilities. We find that sternum evolution was episodic: basal members of Pennaraptora had proportionally small sterna, which became larger and more craniocaudally elongated in Avialae. This enlargement precedes the appearance of a midline ridge, a ..., , # Data from: Enlargement of sternum traits facilitated the evolution of powered flight in birds Associated publication: Lowi-Merri, T.M., Benson, R., Hu, H., et al. Enlargement of sternum traits facilitated the evolution of powered flight in birds. Nat. Ecol. Evol. ## Dryad dataset Dataset DOI: [10.5061/dryad.jsxksn0ng](10.5061/dryad.jsxksn0ng) ## Description of the data and file structure Comparative analysis of fossil stem avian sternum size and dimensions to determine the evolutionary trajectory of the sternum across the dinosaur-bird transition and during the evolution of flight. ### Files and variables Most variables are self-explanatory and are defined when deemed necessary. All units of measurement are in millimetres (mm) unless specified otherwise. #### File: Fossils25.csv **Description:**Â Morphological data on fossil specimens for which sternum size and metrics were collected. ##### Variables * Taxon * Specimen number * Higher Classification: larger clade that the ta...,现代鸟类飞行装置的核心特征为胸骨膨大且龙骨突显著。然而，近鸟类恐龙（Pennaraptora）与早期初鸟类（Avialae）的胸骨要么与现生鸟类差异显著，要么完全缺失，这引发了学界对鸟类胸骨特化结构的演化路径及其与功能的关联的诸多疑问。 由于化石记录零碎不全，且从受压破碎的化石中推断形态与功能存在诸多挑战，该问题至今仍未得到充分解答。本研究采用祖先性状估计法追踪鸟类干群（bird stem group）的胸骨性状演化历程，并通过多变量系统发育回归分析胸骨形态、体重与飞行能力之间的关联。 研究发现胸骨演化具有阶段性：近鸟类恐龙（Pennaraptora）的基干类群胸骨比例偏小，而在初鸟类（Avialae）中，胸骨逐渐变大且沿颅尾轴向延长。这种膨大先于中线脊等结构的出现…… # 数据来源：《胸骨性状膨大助力鸟类动力飞行的演化》 关联发表文献：Lowi-Merri, T.M.、Benson, R.、Hu, H. 等. 胸骨性状膨大助力鸟类动力飞行的演化. 《自然·生态与演化》(Nat. Ecol. Evol.) ## Dryad数据集 数据集DOI：10.5061/dryad.jsxksn0ng ## 数据与文件结构说明 本研究通过对化石鸟类干群的胸骨尺寸与形态参数开展比较分析，旨在明确恐龙向鸟类过渡过程中以及飞行演化历程中胸骨的演化轨迹。 ### 文件与变量 多数变量含义明确，必要时会附详细定义。除特殊说明外，所有测量单位均为毫米（mm）。 #### 文件：Fossils25.csv **描述：** 包含已采集胸骨尺寸与形态参数的化石标本的形态学数据。 ##### 变量 * 分类单元（Taxon） * 标本编号 * 高级分类：该类群所属的更大演化支……