Stephanie E. Pierce2014-05-06 2:38 PM

早期四足鱼石螈的三维肢体关节活动度  Three-dimensional limb joint mobility in the early tetrapod Ichthyostega

论文摘要

四足动物的起源以及从游泳到步行的转变是陆生脊椎动物进化和多样化的一个关键步骤。在此期间,四肢的进化,尤其是关节的专门分化和控制运动的结构,从根本上改变了早期四足动物的行动方式。尽管如此,很少有人了解早期四足动物肢体解剖学的功能性后果以及该解剖学如何影响脊椎动物在该进化的非常关键阶段中的运动能力。在此,我们提出了一个标志性泥盆纪四足鱼石螈的三维重建以及进行了该早期四足动物肢体活动功能的定量和比较分析。 我们表明鱼石螈不可能具有如横向行走的四足动物典型运动行为。特别是它的四肢无法进行能将身体推离地面以及无法交替移动四肢的必需性旋转动作。 由于长轴旋转功能表现在四足变形的鱼类鳍部上,由此可见要么是早期四足动物经历了限制肩关节和髋关节灵活性的初始阶段进行进化要么就是鱼石螈是该方面具有这种唯一性的物种。 我们表明具有鱼石螈骨骼形态和肢体活动的早期四足动物不太可能具有近期所描述的泥盆纪进化轨迹。


Abstract

The origin of tetrapods and the transition from swimming to walking was a pivotal step in the evolution and diversification of terrestrial vertebrates. During this time, modifications of the limbs—particularly the specialization of joints and the structures that guide their motions—fundamentally changed the ways in which early tetrapods could move. Nonetheless, little is known about the functional consequences of limb anatomy in early tetrapods and how that anatomy influenced locomotion capabilities at this very critical stage in vertebrate evolution. Here we present a three-dimensional reconstruction of the iconic Devonian tetrapod Ichthyostega and a quantitative and comparative analysis of limb mobility in this early tetrapod. We show that Ichthyostega could not have employed typical tetrapod locomotory behaviours, such as lateral sequence walking. In particular, it lacked the necessary rotary motions in its limbs to push the body off the ground and move the limbs in an alternating sequence. Given that long-axis rotation was present in the fins of tetrapodomorph fishes, it seems that either early tetrapods evolved through an initial stage of restricted shoulder and hip joint mobility or that Ichthyostega was unique in this respect. We conclude that early tetrapods with the skeletal morphology and limb mobility of Ichthyostega were unlikely to have made some of the recently described Middle Devonian trackways.

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Stephanie E. Pierce

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