Hieronymus Tobin L
Department of Anatomy and Neurobiology, Northeast Ohio Medical University (NEOMED), 4209 St Rt 44, Rootstown, 44272, OH, USA.
BMC Evol Biol. 2015 Feb 27;15:30. doi: 10.1186/s12862-015-0303-7.
Among living fliers (birds, bats, and insects), birds display relatively high aspect ratios, a dimensionless shape variable that distinguishes long and narrow vs. short and broad wings. Increasing aspect ratio results in a functional tradeoff between low induced drag (efficient cruise) and increased wing inertia (difficult takeoff). Given the wide scope of its functional effects, the pattern of aspect ratio evolution is an important factor that contributes to the substantial ecological and phylogenetic diversity of living birds. However, because the feathers that define the wingtip (and hence wingspan and aspect ratio) often do not fossilize, resolution in the pattern of avian wing shape evolution is obscured by missing information. Here I use a comparative approach to investigate the relationship between skeletal proxies of flight feather attachment and wing shape.
An accessory lobe of the internal index process of digit II-1, a bony correlate of distal primary attachment, shows weak but statistically significant relationships to aspect ratio and mass independent of other skeletal morphology. The dorsal phalangeal fossae of digit II-1, which house distal primaries VIII and IX, also show a trend of increased prominence with higher aspect ratio. Quill knobs on the ulna are examined concurrently, but do not show consistent signal with respect to wing shape.
Although quill knobs are cited as skeletal correlates of flight performance in birds, their relationship to wing shape is inconsistent among extant taxa, and may reflect diverging selection pressures acting on a conserved architecture. In contrast, correlates of distal primary feather attachment on the major digit show convergent responses to increasing aspect ratio. In light of the diversity of musculoskeletal and integumentary mophology that underlies wing shape in different avian clades, it is unlikely that a single skeletal feature will show consistent predictive power across Neoaves. Confident inference of wing shape in basal ornithurine birds will require multiple lines of evidence, together with an understanding of clade-specific evolutionary trends within the crown.
在现存的飞行生物（鸟类、蝙蝠和昆虫）中，鸟类展现出相对较高的展弦比，这是一个无量纲的形状变量，用于区分长而窄与短而宽的翅膀。展弦比的增加会在低诱导阻力（高效巡航）和增加的机翼惯性（起飞困难）之间产生功能权衡。鉴于其功能效应范围广泛，展弦比的进化模式是促成现存鸟类丰富的生态和系统发育多样性的一个重要因素。然而，由于界定翼尖（进而界定翼展和展弦比）的羽毛通常不会形成化石，鸟类翅膀形状进化模式的分辨率因信息缺失而变得模糊。在此，我采用比较方法来研究飞行羽毛附着的骨骼替代指标与翅膀形状之间的关系。
第II指第1节指骨内指标突起的一个附属叶，即远端初级飞羽附着的骨骼对应物，显示出与展弦比和质量之间存在微弱但具有统计学意义的确切关系，且与其他骨骼形态无关。容纳远端初级飞羽VIII和IX的第II指第1节指骨的背侧指骨窝，也呈现出随着展弦比增加而突出程度增加的趋势。同时对尺骨上的羽茎瘤进行了研究，但未发现其与翅膀形状存在一致的信号。
尽管羽茎瘤被认为是鸟类飞行性能的骨骼对应指标，但其与翅膀形状的关系在现存分类群中并不一致，可能反映了作用于保守结构的不同选择压力。相比之下，主要指骨上远端初级飞羽附着部位的对应指标对展弦比增加呈现出趋同反应。鉴于不同鸟类类群中构成翅膀形状基础的肌肉骨骼和皮肤形态的多样性，单一的骨骼特征不太可能在新鸟小纲中显示出一致的预测能力。要自信地推断基干今鸟型类鸟类的翅膀形状，需要多条证据线索，同时还要了解冠群内特定类群的进化趋势。
