Gayford Joel H, Jambura Patrick L, Türtscher Julia, Sternes Phillip C, Seamone Scott G, Shimada Kenshu
College of Science and Engineering James Cook University Townsville Queensland Australia.
Shark Measurements London UK.
Ecol Evol. 2025 Aug 29;15(9):e72082. doi: 10.1002/ece3.72082. eCollection 2025 Sep.
Macroevolutionary trends in vertebrate morphology fundamentally shape our understanding of marine ecosystems through deep time. Body form influences interactions between organisms and their environment, dictating their locomotor capabilities and ability to hunt/escape from other species. Sharks (Elasmobranchii: Selachii) have been suggested to broadly exhibit two discrete body forms: one 'shallow-bodied' form associated with slow-moving benthic species and a 'deep-bodied' form typified by highly active pelagic taxa. Until now, no study has addressed the validity or evolution of these body forms in a phylogenetic framework. Hence, we lack understanding of when, why and how the body forms observed in extant species originally evolved. In this study, we reconstruct the evolutionary history of shark body form and provide statistical evidence to suggest three broadly discrete body forms among extant species. We find support for a benthic origin of sharks, with four discrete transitions to a pelagic-type morphology occurring during the Jurassic and Cretaceous. Increased habitat availability during this time, driven by a combination of elevated sea temperature, eustatic sea level rise, continental fragmentation and diversification trends of actinopterygians and marine reptiles, could have facilitated the colonisation of the pelagic realm by Mesozoic sharks and the repeated independent evolution of body form consistent with extant pelagic species. We also propose that habitat availability and its taphonomic consequences may explain discordance between origination times suggested by molecular phylogenies and the fossil record.
脊椎动物形态的宏观进化趋势从根本上塑造了我们对漫长地质时期海洋生态系统的理解。身体形态影响着生物体与其环境之间的相互作用，决定了它们的运动能力以及捕食/躲避其他物种的能力。鲨鱼（板鳃亚纲：鲨总目）被认为大致呈现出两种截然不同的身体形态：一种是与行动缓慢的底栖物种相关的“浅体型 ”形态，另一种是以高度活跃的远洋类群为代表的“深体型 ”形态。到目前为止，尚无研究在系统发育框架内探讨这些身体形态的有效性或进化情况。因此，我们对现存物种中观察到的身体形态最初何时、为何以及如何进化缺乏了解。在这项研究中，我们重建了鲨鱼身体形态的进化历史，并提供统计证据表明现存物种中存在三种大致不同的身体形态。我们发现支持鲨鱼起源于底栖环境的观点，在侏罗纪和白垩纪期间发生了四次向远洋型形态的离散转变。在此期间，由于海水温度升高、海平面上升、大陆分裂以及硬骨鱼类和海洋爬行动物的多样化趋势共同作用，栖息地可用性增加，这可能促进了中生代鲨鱼对远洋领域的殖民以及与现存远洋物种一致的身体形态的反复独立进化。我们还提出，栖息地可用性及其埋藏学后果可能解释了分子系统发育所暗示的起源时间与化石记录之间的不一致。
