Three-dimentionally preserved appendages in an early Cambrian stem-group pancrustacean
Three-dimentionally preserved appendages in an early Cambrian stem-group pancrustacean
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早期寒武纪干群胰甲壳动物三维保存的附肢
DOI：
10.1016/j.cub.2018.11.060
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发表时间：
2018
期刊：
影响因子：
9.2
通讯作者：
翟大有
中科院分区：
文献类型：
--
作者：
翟大有
泛甲壳类动物在整个中生代的生物圈中拥有令人印象深刻的多样性，丰富性和生态影响[1]。分子钟估计表明寒武纪早期泛甲壳类的分歧[2，3]。尽管拥有丰富的古生代特殊化石沉积物[4-7]，但由于难以识别寒武纪形式和现存代表之间的共形，因此Pancrustacea的早期进化仍然难以捉摸。虽然早期的研究表明甲壳类动物与寒武纪双壳真节肢动物有亲缘关系[8-11]，但最近对其形态的重新评估[12-16]已经不再支持这种观点。全甲壳类最好的证据来自于寒武纪微体化石，它们以三维磷酸盐复制物的形式保存在奥斯滕型组合中[4，17-19]或作为“小碳质化石”（SCF）[20，21]。虽然这些埋藏窗口捕捉微小的形态，使现存的代表进行详细的比较，这些微体化石仅限于幼虫阶段（Orsten）或残体（SCF）限制其系统发育的精度[5，12，19，20，22，23]。我们利用X射线计算机断层扫描[24]揭示了中国早寒武世澄江双瓣真节肢动物Ercaicinia multinodosa[25]的三维附肢形态。多节棘皮蛛与clypecaridids [9]、waptiids [16]和hymenocarines [11，14]的相似性表明，这些真节肢动物也可能具有类似的分化附属物，但这些细节受到压实的大型化石保存的限制。E. multinodosa阐明了泛甲壳动物附属物分化的早期演化，并代表了从完整的大型化石中已知的最古老的明确的冠群下颌骨[22]。
Pancrustaceans boast impressive diversity, abundance, and ecological impact in the biosphere throughout the Phanerozoic [1]. Molecular clock estimates suggest an early Cambrian divergence for pancrustaceans [2, 3]. Despite the wealth of Palaeozoic exceptional fossiliferous deposits [4–7], the early evolution of Pancrustacea remains elusive given the difficulty of recognizing synapomorphies between Cambrian forms and extant representatives. Although early studies suggested crustacean affinities for Cambrian bivalved euarthropods [8–11], this view has fallen out of favor by recent reappraisals of their morphology [12–16]. The best evidence for total-group pancrustaceans comes from Cambrian microfossils preserved as three-dimensional phosphatic replicates in Orsten-type assemblages [4, 17–19] or as "small carbonaceous fossils" (SCFs) [20, 21]. Although these taphonomic windows capture minute morphology enabling detailed comparisons with extant representatives, these microfossils are limited to larval stages (Orsten) or recalcitrant fragmentary remains (SCFs) restricting their phylogenetic precision [5, 12, 19, 20, 22, 23]. We employed X-ray computed tomography [24] to reveal the three-dimensionally appendage morphology of the Chengjiang bivalved euarthropodErcaicunia multinodosa[25] from the early Cambrian of China.E. multinodosapossesses characters uniquely shared with extant crustaceans, including differentiated tritocerebral antennae and epipodite-bearing biramous trunk appendages. Similarities betweenE. multinodosawith clypecaridids [9], waptiids [16] and hymenocarines [11, 14] suggest that these euarthropods may also possess similarly differentiated appendages, but these details are obstructed by the limits of preservation of compacted macrofossils.E. multinodosailluminates the early evolution of pancrustacean appendage differentiation and represents the oldest unequivocal crown-group mandibulate known from complete macrofossils [22].