Sharks vary greatly in morphology, physiology, and ecology. Differences in whole body shape, swimming style, and physiological parameters have previously been linked to varied habitat uses. Pectoral fin morphology has been used to taxonomically classify species and hypotheses on the functional differences in shape are noted throughout the literature; however, there are limited comparative datasets that quantify external and skeletal morphology. Further, fins were previously categorized into two discrete groups based on the amount of skeletal support present: (a) aplesodic, where less than half of the fin is supported and (b) plesodic where greater than half of the fin is supported. These discrete classifications have been used to phylogenetically place species, though the methodology of classification is infrequently described. In this study, we sampled fins from 18 species, 6 families, and 3 orders, which were also grouped into five ecomorphotype classifications. We examined the external morphology, extent of skeletal support, and cross‐sectional shape of individual cartilaginous elements. Using phylogenetic comparative methods, we show that fin shape does not differ significantly between ecomorphotypes, suggesting there may be some mechanical constraint. However, we find that the internal anatomy of the fin does vary significantly between ecomorphotypes, especially the extent and distribution of calcification of skeletal support, suggesting that the superficial similarity of fin shapes across ecomorphotypes may belie differences in function. Finally, we find that a number of morphological variables such as number of radials, radial calcification and shape, and fin taper all correlate with the extent of skeletal support. Within these morphospaces, we also describe that some orders/families tend to occupy certain areas with limited overlap. While we demonstrate that there is some mechanical constraint limiting external variations in shark pectoral fin morphology, there are compounding differences in skeletal anatomy that occur within ecomorphotypes which we propose may affect function.

中文翻译：

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鲨鱼胸鳍形态比较

鲨鱼在形态、生理和生态方面差异很大。全身形状、游泳方式和生理参数的差异以前与栖息地的不同用途有关。胸鳍形态已被用于对物种进行分类，并且在整个文献中都提到了关于形状功能差异的假设；然而，量化外部和骨骼形态的比较数据集有限。此外，根据存在的骨骼支撑量，鳍先前被分为两个独立的组：(a) aplesodic，其中支撑少于一半的鳍；(b) plesodic，其中支撑超过一半的鳍。尽管很少描述分类方法，但这些离散分类已被用于对物种进行系统发育定位。在这项研究中，我们从 18 个物种、6 个科和 3 个目中取样，它们也被分为五个生态形态分类。我们检查了单个软骨元素的外部形态、骨骼支撑范围和横截面形状。使用系统发育比较方法，我们表明不同生态形态类型之间的鳍形状没有显着差异，这表明可能存在一些机械约束。然而，我们发现不同生态形态类型的鳍的内部解剖结构确实存在显着差异，尤其是骨骼支持钙化的程度和分布，这表明不同生态形态类型的鳍形状的表面相似性可能掩盖了功能的差异。最后，我们发现许多形态变量，如放射状数量、放射状钙化和形状，和鳍锥度都与骨骼支撑的程度相关。在这些形态空间中，我们还描述了一些订单/家庭倾向于占据某些重叠有限的区域。虽然我们证明有一些机械约束限制了鲨鱼胸鳍形态的外部变化，但在我们提出的可能影响功能的生态形态类型中，骨骼解剖结构存在复合差异。