Data from: Body shape diversity in Triassic‒Early Cretaceous neopterygian fishes: sustained holostean disparity and predominantly gradual increases in teleost phenotypic variety

Comprising Holostei and Teleostei, the ~32,000 species of neopterygian fishes are anatomically disparate and represent the dominant group of aquatic vertebrates today. However, the pattern by which teleosts rose to represent almost all of this diversity, while their holostean sister group dwindled to 8 extant species and two broad morphologies, is poorly constrained. A geometric morphometric approach was taken to generate a morphospace from over 400 fossil taxa, representing almost all articulated neopterygian taxa known from the first 150 million years—roughly 60%—of history (Triassic‒Early Cretaceous). Patterns of morphospace occupancy and disparity are examined in order to: assess evidence for a phenotypically 'dominant' holostean phase; evaluate whether expansions in teleost phenotypic variety are predominantly abrupt or gradual, including assessment of whether apomorphy-defined teleosts are as morphologically conservative as typically assumed; compare diversification in crown and stem teleosts. The systematic affinities of dapediiforms and pycnodontiforms, two extinct neopterygian clades of uncertain phylogenetic placement, significantly impact patterns of morphological diversification. For instance, alternative placements dictate whether or not holosteans possessed statistically higher disparity than teleosts in the Late Triassic and Jurassic. Despite this ambiguity, all scenarios agree that holosteans do not exhibit a decline in disparity during the Early Triassic‒Early Cretaceous interval, but instead maintain their Toarcian‒Callovian variety until the end of the Early Cretaceous without substantial further expansions. After a conservative Induan‒Carnian phase, teleosts colonize (and persistently occupy) novel regions of morphospace in a predominantly gradual manner until the Hauterivian, after which expansions are rare. Furthermore, apomorphy-defined teleosts possess greater phenotypic variety than typically assumed. Comparison of crown and stem teleost partial disparity indicates that, despite substantial expansion in crown teleosts between the Late Jurassic and earliest Cretaceous, stem teleosts remained important long-term contributors to overall teleost disparity during this time.

新鳍鱼类（Neopterygii）现存约32000个物种，涵盖全骨鱼下纲（Holostei）与真骨鱼下纲（Teleostei），其解剖学特征高度多样，是当前水生脊椎动物中的优势类群。然而，真骨鱼如何演化成为该类群多样性的绝对主体，而其姊妹群全骨鱼却锐减至仅存8个物种、仅保留两种宽泛形态类型的这一演化模式，目前仍缺乏明确约束。本研究采用几何形态测量法（geometric morphometrics），基于400余个化石类群构建形态空间（morphospace），这些类群涵盖了前1.5亿年（约占演化历史的60%）中已知的几乎所有关联保存的新鳍鱼类类群，时间跨度为三叠纪至早白垩世。本研究对形态空间占据模式与形态差异度展开分析，旨在达成以下目标：一是评估是否存在表型上占据优势的全骨鱼演化阶段；二是探究真骨鱼表型多样性的扩张主要以突发式还是渐进式为主，同时验证基于衍征（apomorphy）定义的真骨鱼是否如通常所假设的那样在形态上具有高度保守性；三是比较冠群真骨鱼与干群真骨鱼的多样化模式。褶外骨鱼目（Dapediiformes）与扁体鱼目（Pycnodontiformes）是两类系统发育位置尚不明确的已绝灭新鳍鱼类支系，它们的系统发育亲缘关系会显著影响形态多样化的分析结果。例如，不同的系统发育位置假设会决定：在晚三叠世与侏罗纪时期，全骨鱼的形态差异度是否在统计学上显著高于真骨鱼。尽管存在上述歧义，但所有分析场景均表明：全骨鱼在早三叠世至早白垩世期间并未出现形态差异度的下降，反而维持了其在托阿尔阶至卡洛夫阶时期的形态多样性，直至早白垩世末期都未出现显著的进一步扩张。在经历了印度阶至卡尼阶的保守演化阶段后，真骨鱼以渐进式扩张为主，持续占据新的形态空间区域，直至豪特里维阶；此后其多样性扩张事件则较为罕见。此外，基于衍征定义的真骨鱼所拥有的表型多样性，远超此前的普遍假设。对冠群与干群真骨鱼的部分形态差异度进行比较后发现：尽管晚侏罗世至早白垩世早期冠群真骨鱼的多样性出现了显著扩张，但干群真骨鱼在此期间仍是整体真骨鱼形态差异度的长期重要贡献者。