Department of Earth Sciences, University of Bristol, Queens Road, Bristol, UK.
Proc Biol Sci. 2010 Apr 7;277(1684):1121-7. doi: 10.1098/rspb.2009.1899. Epub 2009 Dec 9.
Pterosaurs, flying reptiles from the Mesozoic, had wing membranes that were supported by their arm bones and a super-elongate fourth finger. Associated with the wing, pterosaurs also possessed a unique wrist bone--the pteroid--that functioned to support the forward part of the membrane in front of the leading edge, the propatagium. Pteroid shape varies across pterosaurs and reconstructions of its orientation vary (projecting anteriorly to the wing leading edge or medially, lying alongside it) and imply differences in the way that pterosaurs controlled their wings. Here we show, using biomechanical analysis and considerations of aerodynamic efficiency of a representative ornithocheirid pterosaur, that an anteriorly orientated pteroid is highly unlikely. Unless these pterosaurs only flew steadily and had very low body masses, their pteroids would have been likely to break if orientated anteriorly; the degree of movement required for a forward orientation would have introduced extreme membrane strains and required impractical tensioning in the propatagium membrane. This result can be generalized for other pterodactyloid pterosaurs because the resultant geometry of an anteriorly orientated pteroid would have reduced the aerodynamic performance of all wings and required the same impractical properties in the propatagium membrane. We demonstrate quantitatively that the more traditional reconstruction of a medially orientated pteroid was much more stable both structurally and aerodynamically, reflecting likely life position.
翼龙是中生代的飞行爬行动物，它们的翅膀膜由臂骨和超级细长的第四指支撑。与翅膀相关联的是，翼龙还拥有独特的腕骨——翼骨，它的作用是支撑膜的前缘部分，即前翼膜。翼骨形状在翼龙之间有所不同，对其方向的重建也有所不同（向前翼前缘或向中线突出，与翼前缘并排），这表明翼龙控制翅膀的方式存在差异。在这里，我们使用生物力学分析和对代表性的鸟掌翼龙的空气动力学效率的考虑，表明向前定向的翼骨极不可能。除非这些翼龙只稳定地飞行且体重非常低，否则如果向前定向，它们的翼骨很可能会断裂；向前定向所需的运动程度会引入极端的膜应变，并需要在前翼膜中使用不切实际的张力。这个结果可以推广到其他翼手龙类翼龙，因为向前定向的翼骨的结果几何形状会降低所有翅膀的空气动力学性能，并在前翼膜中需要相同的不切实际的特性。我们定量地证明，更传统的中线定向翼骨在结构和空气动力学上都更加稳定，反映了可能的生活位置。
