Budd Graham E
Department of Earth Sciences (Historical Geology and Palaeontology), Uppsala University, Norbyvägen 22, Uppsala, Sweden.
Nature. 2002 May 16;417(6886):271-5. doi: 10.1038/417271a.
The composition of the arthropod head has been one of the most controversial topics in zoology, with a large number of theories being proposed to account for it over the last century. Although fossils have been recognized as being of potential importance in resolving the issue, a lack of consensus over their systematics has obscured their contribution. Here, I show that a group of previously problematic Cambrian arthropods from the Burgess Shale and Chengjiang faunas form a clade close to crown-group euarthropods, the group containing myriapods, chelicerates, insects and crustaceans. They are characterized by modified or even absent endopods, and two pre-oral appendages. Comparison with reconstructions of the crown-group euarthropod ground plan and recent investigations into onychophorans demonstrates that these two appendages are the first antenna (of extant crustaceans) and a more anterior appendage associated with an ocular segment. The latter appendage has been reduced in all crown-group euarthropods. Its most likely relic is as a component of the labrum. These fossils thus tie together results from disparate living groups (onychophorans and euarthropods).
节肢动物头部的组成一直是动物学中最具争议的话题之一，在过去的一个世纪里，人们提出了大量理论来解释这一问题。尽管化石被认为在解决该问题方面具有潜在重要性，但对其分类学缺乏共识掩盖了它们的贡献。在这里，我表明，来自布尔吉斯页岩和澄江动物群的一组先前存在问题的寒武纪节肢动物形成了一个与冠群真节肢动物接近的进化枝，冠群真节肢动物包括多足类、螯肢类、昆虫和甲壳类。它们的特征是内肢经过修饰甚至缺失，以及两个口前附肢。与冠群真节肢动物基础形态的重建以及近期对有爪动物的研究进行比较表明，这两个附肢分别是（现存甲壳类动物的）第一触角和与眼节相关的更靠前的附肢。后一个附肢在所有冠群真节肢动物中都已退化。它最可能的遗迹是上唇的一个组成部分。因此，这些化石将来自不同生物类群（有爪动物和真节肢动物）的研究结果联系在了一起。
