Palaeo-Evo-Devo of Malacostraca – quantifying crabs and their relatives

螃蟹及其近亲共同代表着Meiura组，今天存在于具有大量物种的不同生态系统中。除了不同的海洋栖息地外，在淡水和陆地栖息地也可以找到Meiura的代表。Meiura群具有相当大的经济重要性，其代表发挥着不同的生态作用。Meiura组的很大一部分生态多样性是由幼虫阶段代表的，幼虫阶段构成了浮游生物的重要组成部分。此外，在化石记录中，已知大量的美村代表，最早的记录来自中生代。据推测，这些甲壳类动物在当时的生态系统中已经发挥了重要作用。特别是在白垩纪，基于大量的成年蟹和近亲的化石，美浦组的代表似乎有了显著的多样化。不幸的是，人们对未成熟阶段几乎一无所知，包括以Meiura为代表的化石的幼虫，尽管这些知识对于了解化石生态系统很重要。在这个项目中，计划采用一种新的方法来解决缺乏Meiura组化石幼虫的问题。我们假设，这种缺失并不一定意味着这些化石不存在，相反，它们往往没有被认识到。其原因是，特别是后期的幼虫，即所谓的巨眼幼虫，可以根据躯干和附属物的特征确定为这样的幼虫。然而，在恐龙化石中，通常只发现盾牌和/或海龟。在现存的三栖动物中，这些结构的个体发育变化是已知的，但这些变化相当微妙，不容易被检测为定性和离散的特征。因此，我们在这个项目中的方法是收集盾牌和螯合体形状的定量数据，并对它们进行比较。通过这种方式，可以得出一些结论：1)可以这样识别不同的巨眼幼虫和早期幼虫阶段。2)现代与化石的个体发育模式可以进行比较(古生-演化-演化)。3)可以检测到不同阶段的体型变化。为了量化形状，将使用椭圆傅立叶分析来研究轮廓，该分析已经成功地应用于类似的研究。利用这些数据，应该比较美浦组内不同进化谱系的变化。在同一时间，不同血统的类似变化意味着对相同环境变化的相同方向的反应。通过这种方式，这些数据也有助于对气候变化的总体理解。

Crabs and their closer relatives, together representing the group Meiura, are today present in diverse ecosystems with a large number of species. Besides different marine habitats, representatives of Meiura can also be found in freshwater and terrestrial habitats. The group Meiura is of considerable economic importance, and its representatives fulfil diverse ecological roles. A large part of the ecological diversity of the group Meiura is represented by the larval stages, which comprise a significant part of the plankton. Also in the fossil record, representatives of Meiura are known in large numbers, the earliest record being from the Mesozoic. Presumably, these crustaceans have already played an important role in the ecosystems at that time. Especially in the Cretaceous representatives of the group Meiura appear to have diversified significantly, based on numerous fossils of adult crabs and close relatives. Unfortunately, almost nothing is known about the immature stages including the larvae of the fossil representatives of Meiura, even though this knowledge would be important for the understanding of fossil ecosystems. In this project, it is planned to follow a new approach to tackle the problem of the lack of fossil larvae of the group Meiura. We assume that this lack does not necessarily mean that those fossils do not exist, but instead that they are often not recognised as such. The reason for this is that especially the later larval stages, the so-called megalopa larvae, can be determined as such based on characters of the trunk and the appendages. In fossil meiurans, however, usually only the shield and/or the chelae are found. In extant meiurans, ontogenetic changes of these structures are known, yet these are rather subtle and cannot easily be detected as qualitative and discrete characters. Hence, our approach in this project is to gather quantitative data of the shape of shield and chelae and to compare these. In this way, a number of conclusions can be drawn: 1) Distinct megalopa larvae and early juvenile stages can be identified as such. 2) Ontogenetic patterns can be compared between modern and fossil representatives (palaeo-evo-devo). 3) Changes in body size of distinct stages can be detected. To quantify the shape, the outline will be investigated with Elliptic Fourier Analysis, which has already been successfully applied for similar studies. With these data, changes in different evolutionary lineages within the group Meiura should be compared. Similar changes in different lineages at the same time would imply reactions in the same direction on the same changes of the environment. In this way, such data also contribute to a general understanding of a changing climate.