Yunnan Key Laboratory for Palaeobiology, Yunnan University, 2 North Cuihu Road, Kunming, 650091, People's Republic of China.
MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, 2 North Cuihu Road, Kunming, 650091, People's Republic of China.
BMC Biol. 2024 Apr 29;22(1):96. doi: 10.1186/s12915-024-01889-y.
The early Cambrian arthropod clade Megacheira, also referred to as great appendage arthropods, comprised a group of diminutive and elongated predators during the early Palaeozoic era, around 518 million years ago. In addition to those identified in the mid-Cambrian Burgess Shale biota, numerous species are documented in the renowned 518-million-year-old Chengjiang biota of South China. Notably, one species, Tanglangia longicaudata, has remained inadequately understood due to limited available material and technological constraints. In this study, we, for the first time, examined eight fossil specimens (six individuals) utilizing state-of-the-art μCT and computer-based 3D rendering techniques to unveil the hitherto hidden ventral and appendicular morphology of this species.
We have identified a set of slender endopodites gradually narrowing distally, along with a leaf-shaped exopodite adorned with fringed setae along its margins, and a small putative exite attached to the basipodite. Our techniques have further revealed the presence of four pairs of biramous appendages in the head, aligning with the recently reported six-segmented head in other early euarthropods. Additionally, we have discerned two peduncle elements for the great appendage. These findings underscore that, despite the morphological diversity observed in early euarthropods, there exists similarity in appendicular morphology across various groups. In addition, we critically examine the existing literature on this taxon, disentangling previous mislabelings, mentions, descriptions, and, most importantly, illustrations.
The μCT-based investigation of fossil material of Tanglangia longicaudata, a distinctive early Cambrian euarthropod from the renowned Chengjiang biota, enhances our comprehensive understanding of the evolutionary morphology of the Megacheira. Its overall morphological features, including large cup-shaped eyes, raptorial great appendages, and a remarkably elongated telson, suggest its potential ecological role as a crepuscular predator and adept swimmer in turbid waters.
早寒武纪节肢动物巨肢类，也被称为大附肢节肢动物，是一组在大约 5.18 亿年前的古生代早期出现的小型、细长的掠食者。除了在中寒武纪伯吉斯页岩生物群中发现的物种外，在中国南方著名的 5.18 亿年前澄江生物群中也有大量物种被记录。值得注意的是，有一种名为长尾巨肢虾的物种由于可用材料有限和技术限制，其了解程度仍然不够。在这项研究中，我们首次使用最先进的μCT 和基于计算机的 3D 渲染技术检查了 8 个化石标本（6 个个体），揭示了该物种迄今为止隐藏的腹侧和附肢形态。
我们已经确定了一组逐渐变细的内附肢，远端逐渐变细，还有一个带有羽状外肢的叶状外肢，边缘有带毛的刚毛，以及一个附着在基节上的小外突。我们的技术还进一步揭示了头部存在四对双肢的附肢，与最近在其他早期真节肢动物中报告的六节头部相吻合。此外，我们还发现了两个用于大附肢的花梗元素。这些发现表明，尽管早期真节肢动物表现出形态多样性，但不同群体之间的附肢形态存在相似性。此外，我们还批判性地检查了该分类群的现有文献，梳理了以前的错误标记、提及、描述，最重要的是，插图。
基于μCT 的对来自著名澄江生物群的早期寒武纪真节肢动物长尾巨肢虾化石材料的研究，增强了我们对巨肢类进化形态的全面理解。它的整体形态特征，包括大型杯状眼睛、捕食性的大附肢和非常长的尾刺，表明它可能在黄昏时作为掠食者和在浑浊的水中游泳的能手存在。
