Abstract: Statistic analyses of the proportions of the three major bones of the hindlimb (femur, tibiotarsus and tarsometatarsus) from 137 skeletons belonging to 59 families of 18 orders of living birds with different perching habits show that they can be used as a good indicator of their living styles. Measurements of the length of the hindlimb bones indicated that the tibiotarsus is invariably the largest among the three major leg bones. We also found that the femur is shorter than the tarsometatarsus in terrestrial birds while the reverse is true in arboreal birds. We also analyzed the leg bone proportions of 14 species of Mesozoic birds from the Early Cretaceous of China by using ternary diagrams and comparison with 21 specimens of Cenozoic (Paleogene and Neogene) birds，and concluded that the Early Cretaceous enantiornithines are typical arboreal birds, more basal birds from the Mesozoic are mainly arboreal with some adapted for scansorial life, and the ornithurines are characterized by both arboreal and terrestrial adaptations. Our work, combined with the phylogenetical framework of bird evolution, confirms that the arboreal adaptation represents a primitive condition for early birds, which provides further evidence for the arboreal hypothesis of the origin of bird flight. The differentiation of the perching habits of early birds demonstrates that they expanded their ecological niches and food resources during the competitions among themselves and with contemporaneous vertebrates.

摘要： 通过对18目59科137例现生不同栖息习性鸟类的后肢3块骨骼(股骨、胫跗骨和跗跖骨)长度比例的观察和特征分析，推断出鸟类的栖息习性与后肢3块骨骼中各骨骼长度所占总长度的比例存在密切的关系。即在所有鸟类的后肢骨骼中，胫跗骨的长度占3块骨骼的比例为最大；地栖鸟类后肢骨骼中股骨的长度要短于跗跖骨；树栖鸟类后肢骨骼中股骨的长度要长于跗跖骨。鸟类后肢3块骨骼的长度比例特征是鸟类长期对栖息等行为适应的结果。在此基础上，对中国中生代14例鸟类的栖息习性进行了分析，利用三元投影的统计方法，并以国内外新生代(古近纪和新近纪)21例鸟类标本作为对比参考，得出辽西中生代不同类型鸟类的栖息行为特征：基干鸟类以树栖为主要习性，其中个别鸟类还具有攀援的习性，而反鸟类则是典型的树栖鸟类，今鸟类兼有树、地栖的习性。研究表明，在现行的鸟类系统发育框架下，树栖适应(及攀援)代表了鸟类演化历史中最原始的生活方式。这一结论也支持鸟类飞行的树栖起源假说。中生代鸟类栖息习性分异的多样性反映了早期鸟类演化过程中自身以及与其他同期生物在生态空间和食物资源的竞争的加剧和对环境的不断适应。