State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering and Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing 210023, China.
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences, Nanjing 210008, China.
Science. 2022 Jul 8;377(6602):218-222. doi: 10.1126/science.abm2708. Epub 2022 Jul 7.
Pharyngeal arches are a key innovation that likely contributed to the evolution of the jaws and braincase of vertebrates. It has long been hypothesized that the pharyngeal (branchial) arch evolved from an unjointed cartilaginous rod in vertebrate ancestors such as that in the nonvertebrate chordate amphioxus, but whether such ancestral anatomy existed remains unknown. The pharyngeal skeleton of controversial Cambrian animals called yunnanozoans may contain the oldest fossil evidence constraining the early evolution of the arches, yet its correlation with that of vertebrates is still disputed. By examining additional specimens in previously unexplored techniques (for example, x-ray microtomography, scanning and transmission electron microscopy, and energy dispersive spectrometry element mapping), we found evidence that yunnanozoan branchial arches consist of cellular cartilage with an extracellular matrix dominated by microfibrils, a feature hitherto considered specific to vertebrates. Our phylogenetic analysis provides further support that yunnanozoans are stem vertebrates.
咽弓是一个关键的创新，可能有助于脊椎动物的颌骨和脑壳的进化。长期以来，人们一直假设咽（鳃）弓是从无关节的软骨杆进化而来的，这种软骨杆存在于脊椎动物的祖先中，如非脊椎动物脊索动物文昌鱼，但这种祖先解剖结构是否存在仍然未知。被称为昆明鱼形动物的有争议的寒武纪动物的咽骨可能包含最古老的化石证据，限制了拱的早期进化，但它与脊椎动物的相关性仍然存在争议。通过使用以前未探索过的技术（例如，X 射线微断层扫描、扫描和透射电子显微镜以及能量色散光谱元素映射）检查更多的标本，我们发现了证据表明，昆明鱼形动物的鳃弓由细胞软骨组成，细胞外基质主要由微纤维组成，这一特征迄今被认为是脊椎动物所特有的。我们的系统发育分析进一步支持了昆明鱼形动物是脊椎动物的祖先。
