Department of Paleontology, University of Vienna, Vienna, Austria.
School of Marine Science and Technology, Faculty of Marine Science and Technology, Tokai University, Shizuoka Shimizu-ku, Japan.
J Fish Biol. 2020 Jul;97(1):212-224. doi: 10.1111/jfb.14352. Epub 2020 May 19.
Chlamydoselachus anguineus, Garman 1884, commonly called the frilled shark, is a deep-sea shark species occurring up to depths of 1300 m. It is assumed to represent an ancient morphotype of sharks (e.g., terminal mouth opening, more than five gill slits) and thus is often considered to represent plesiomorphic traits for sharks. Therefore, its early ontogenetic developmental traits are important for understanding the evolution of its particular phenotype. Here, we established six stages for prenatal embryos and used linear measurements and geometric morphometrics to analyse changes in shape and size as well as their timing during different embryonic stages. Our results show a change in head shape and a relocation of the mouth opening at a late stage of development. We also detected a negative allometric growth of the head and especially the eye compared to the rest of the body and a sexual dimorphism in total body length, which differs from the known data for adults. A multivariate analysis of covariance shows a significant interaction of shape related to the logarithm of centroid size and developmental stage. Geometric morphometrics results indicate that the head shape changes as a covariate of body size while not accounting for differences between sexes. The growth pattern of stages 32 and 33 indicates a shift in head shape, thus highlighting the moment in development when the jaws start to elongate anteriorly to finally achieve the adult condition of terminal mouth opening rather than retaining the early embryonic subterminal position as is typical for sharks. Thus, the antero-terminal mouth opening of the frilled shark has to be considered a derived feature.
皱鳃鲨，又称拟鳗鲛，是一种深海鲨鱼，生活在水深 1300 米的海域。它被认为是鲨鱼古老形态的代表（例如，嘴部末端开口，超过五对鳃裂），因此通常被认为代表了鲨鱼的原始特征。因此，它早期的个体发育特征对于理解其特殊表型的进化至关重要。在这里，我们确定了产前胚胎的六个阶段，并使用线性测量和几何形态测量来分析形状和大小的变化以及它们在不同胚胎阶段的发生时间。我们的结果表明，在发育后期，头部形状发生了变化，口部开口的位置发生了迁移。我们还检测到头和眼睛相对于身体其他部分的负异速生长，以及全长的性二型性，这与已知的成年数据不同。协方差的多元分析表明，形状与中心体大小对数和发育阶段的交互作用具有统计学意义。几何形态测量结果表明，头部形状随身体大小的变化而变化，而不考虑性别差异。阶段 32 和 33 的生长模式表明头部形状发生了变化，从而突出了在发育过程中，颌骨开始向前伸长以最终达到成年的末端开口状态，而不是保留早期胚胎的次末端位置，这是鲨鱼的典型特征。因此，皱鳃鲨的前末端开口必须被视为衍生特征。
