Highly elongate body plans have evolved multiple times in the Actinopterygii, and members of many of these groups are known to use lateral undulation on land. Here, we quantified components of the axial skeleton for four phylogenetically disparate actinopterygian fishes and one sarcopterygian to determine whether axial morphology may affect their locomotor kinematics. We tested species in water and on two terrestrial substrates: loose wet pebbles and wet sand. Differences in axial morphology translated to differences in wavelengths, amplitudes, and frequencies at the center of the body and tail while swimming, but overall, we consistently observed a similar shift in kinematic patterns when fish were moving on the two terrestrial treatments. Generally, our kinematic data support our hypothesis that elongate fishes increased their wave frequency and shorten their wavelengths on terrestrial substrates but we also observed lower wave amplitudes contrary to our prediction. As anticipated, animals exhibited a higher distance ratio (DR), our metric of locomotor efficiency, at the head, center of the body, and tail in aquatic trials. DRs were between 25% and 50% higher in water compared to terrestrial treatments. Locomotion was less effective on wet sand substrate compared to loose wet pebble substrate as exhibited by the discrepancy in DRs and wave patterns along the fish. These data suggest that loose wet pebble substrates do indeed provide vertical points for lateral force transmission and that highly elongate fish have an advantage when moving along this substrate. Our species varied greatly in their total vertebral numbers, 93–129, and in their proportion of precaudal (42–102) and caudal vertebral numbers (10–64). Therefore, despite major differences in vertebral proportions, we find that fishes with anguilliform body plans share similar suites of kinematic patterns within aquatic versus terrestrial treatments and that a pebble substrate can better facilitate axial movements.

中文翻译：

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细长鱼类的陆地运动：探索形态和基质在促进运动中的作用

Actinopterygii 中高度细长的身体结构已经进化了多次，并且已知这些群体中的许多成员在陆地上使用横向起伏。在这里，我们量化了四种系统发育不同的放线鱼类和一种肉翅目鱼类的轴向骨骼的组成部分，以确定轴向形态是否会影响它们的运动学。我们在水中和两个陆地基质上测试了物种：松散的湿鹅卵石和湿沙。轴向形态的差异转化为游泳时身体和尾部中心的波长、振幅和频率的差异，但总的来说，当鱼在两种陆地处理上移动时，我们始终观察到运动学模式的类似变化。一般来说，我们的运动学数据支持我们的假设，即细长的鱼类在陆地基底上增加了它们的波频率并缩短了它们的波长，但我们也观察到了与我们的预测相反的较低的波幅。正如预期的那样，在水生试验中，动物在头部、身体中心和尾部表现出更高的距离比 (DR)，这是我们衡量运动效率的指标。与陆地处理相比，水中的 DR 高出 25% 至 50%。与松散的湿卵石基质相比，湿砂基质上的运动效果较差，如 DR 和沿鱼的波浪图案的差异所表现出的那样。这些数据表明，松散的湿卵石基质确实为横向力传递提供了垂直点，并且高度细长的鱼在沿着该基质移动时具有优势。我们物种的总椎骨数（93-129）以及前尾椎骨数（42-102）和尾椎数（10-64）的比例差异很大。因此，尽管脊椎比例存在重大差异，我们发现具有鳗鱼形身体计划的鱼类在水生和陆生处理中具有相似的运动模式套件，并且卵石基质可以更好地促进轴向运动。