The caudal fin of teleosts is a highly diverse morphological structure and a valuable source of information for comparative analyses. Within the Atherinomorpha a high variation of conditions of the caudal-fin skeleton can be found. These range from complex but basal configurations to simple yet derived configurations. When comparing atherinomorph taxa, it is often difficult to decide on the homology of skeletal elements if only considering adult specimens. However, observing the development of caudal-fin skeletons allows one to evaluate complex structures, reveal homologies and developmental patterns, and even reconstruct the grundplan of the examined taxa. We studied the development of the caudal-fin skeleton in different atheriniform, beloniform and cyprinodontiform species using cleared and stained specimens. Subsequently we compared the development to find similarities and differences in terms of 1) which structures are formed and 2) which structures fuse during ontogeny. For many structures, i.e., the parhypural, the epural(s), the haemal and neural spines of the preural centra and the uroneural, there were either no or only minor differences visible between the three taxa. However, the development of the hypurals revealed a high variation of fusions within different taxa that partly occurred independently in atheriniforms, beloniforms and cyprinodontiforms. Moreover, comparing the development of the ural centra exposed two ways of formation of the compound centrum: 1) in atheriniforms and the beloniforms Oryzias and Hyporhamphus limbatus two ural centra develop and fuse during ontogeny while 2) in cyprinodontiforms and Exocoetidae (Beloniformes) only a single ural centrum is formed during ontogeny. We were able to reconstruct the grundplan of the developmental pattern of the caudal-fin skeleton of the Atheriniformes, Beloniformes and Cyprinodontiformes as well as their last common ancestors. We found two developmental modes of the compound centrum within the Atherinomorpha, i.e., the fusion of two developing ural centra in atheriniforms and beloniforms and the development of only one ural centrum in cyprinodontiforms. Further differences and similarities for the examined taxa are discussed, resulting in the hypothesis that the caudal-fin development of a last common ancestor to all atherinomorphs is very much similar to that of extant atheriniforms.

中文翻译：

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尾鳍骨架的发育揭示了Atherinomorpha内的多个会聚融合

硬骨鱼的尾鳍是高度多样的形态结构，是进行比较分析的有价值的信息来源。在Atherinomorpha内，可以发现尾鳍骨架状况的高度变化。这些范围从复杂但基本的配置到简单但派生的配置。比较动脉粥样硬化类群时，如果仅考虑成年标本，通常很难决定骨骼元素的同源性。但是，观察尾鳍骨骼的发育可以评估复杂的结构，揭示同质性和发育模式，甚至可以重建被检类群的整体计划。我们使用清洁和染色的标本研究了在不同的动脉粥样硬化，贝隆状和鲤齿状物种中尾鳍骨架的发育。随后，我们比较了开发过程，发现了以下方面的异同：1）形成了哪些结构，以及2）在个体发育过程中哪些结构融合了。对于许多结构，即前房中央和尿道神经的旁突，外膜，血和神经刺，这三个类群之间没有或只有很小的差异。然而，透明质酸的发展揭示了不同分类群内融合的高度变化，部分地独立发生于斑节状，贝隆状和犬齿状。此外，比较耳道中枢的发育揭示了复合中枢的两种形成方式：1）在动脉粥样虫和贝隆虫中，稻纵行的两个稻谷发育并融合，而2）在犬齿龙和外Ex科（Beloniformes）的个体发育过程中仅形成了一个单一的乌耳中枢。我们能够重建Atheriniformes，Beloniformes和Cyprinodontiformes以及它们的最后祖先的尾鳍骨架发育模式的grundplan。我们发现了Atherinomorpha内复合中心的两种发育模式，即在动脉粥样形式和贝尼状下的两个发育中的乌拉尔中心的融合，以及在cydonnodontiforms中仅一个乌拉尔中枢的发展。讨论了所检查的分类单元的其他差异和相似之处，