The magnitude and ontogenetic patterns of intraspecific variation can provide important insights into the evolution and development of organisms. Understanding the intraspecific variation of organisms is also a key to correctly pursuing studies in major fields of palaeontology. However, intraspecific variation has been largely overlooked in ectocochleate cephalopods, particularly nautilids. Furthermore, little is known regarding the evolutionary pattern. Here, we present morphological data for the Cretaceous nautilid Eutrephoceras dekayi (Morton) and the modern nautilid Nautilus pompilius Linnaeus through ontogeny. The data are used to describe conch morphology and to elucidate the evolutionary patterns of intraspecific variation. We discovered a similar overall pattern of growth trajectories and the presence of morphological changes at hatching and maturity in both taxa. We also found that intraspecific variation is higher in earlier ontogeny than in later ontogeny in both taxa. The high variation in earlier ontogeny may imply increased flexibility in changing the timing of developmental events, which probably played an important role in nautilid evolution. We assume that the decrease in variation in later ontogeny reflects developmental constraints. Lastly, we compared the similarity/dissimilarity of ontogenetic patterns of variation between taxa. Results reveal that the similarity/dissimilarity of the ontogenetic pattern differs between E. dekayi and N. pompilius. We conclude that this shift in the ontogenetic pattern of variation may be rooted in changes in the developmental programme of nautilids through time. We propose that studying ontogenetic patterns of intraspecific variation can provide new insights into the evolution and development of organisms.

中文翻译：

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通过个体发育的种内变异模式：以白垩纪鹦鹉螺Eutrephoceras dekayi和现代鹦鹉螺为例

种内变异的大小和个体发育模式可以为生物的进化和发育提供重要的见识。理解生物的种内变异也是正确开展古生物学主要领域研究的关键。然而，种内变异在外胚突头足类特别是鹦鹉螺中已被大大忽略。此外，关于进化模式知之甚少。在这里，我们介绍了白垩纪鹦鹉螺Eutrephoceras dekayi（莫顿）和现代鹦鹉螺鹦鹉螺的形态学数据。林奈通过个体发育。该数据用于描述海螺形态并阐明种内变异的进化模式。我们发现了两个类群中相似的生长轨迹总体模式以及孵化和成熟时的形态变化。我们还发现在两个类群中，较早的个体发育中种内变异高于较晚的个体发育。早期个体发育的高变异性可能意味着在改变发育事件发生的时间方面增加了灵活性，这可能在鹦鹉螺的进化中起了重要作用。我们假设后期个体差异的减少反映了发育方面的限制。最后，我们比较了分类单元之间个体发生模式变异的相似性/不相似性。E. dekayi和N. pompilius。我们得出的结论是，个体发生方式的这种转变可能是由于鹦鹉螺随着时间的发展而发生的变化。我们建议研究种内变异的遗传模式可以为生物的进化和发展提供新的见解。