State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China.
Department of Biological Sciences, The George Washington University, Washington, DC, USA.
Nat Ecol Evol. 2018 Apr;2(4):623-627. doi: 10.1038/s41559-018-0475-9. Epub 2018 Feb 5.
Understanding the genealogical relationships among the arachnid orders is an onerous task, but fossils have aided in anchoring some branches of the arachnid tree of life. The discovery of Palaeozoic fossils with characters found in both extant spiders and other arachnids provided evidence for a series of extinctions of what was thought to be a grade, Uraraneida, that led to modern spiders. Here, we report two extraordinarily well-preserved Mesozoic members of Uraraneida with a segmented abdomen, multi-articulate spinnerets with well-defined spigots, modified male palps, spider-like chelicerae and a uropygid-like telson. The new fossils, belonging to the species Chimerarachne yingi, were analysed phylogenetically in a large data matrix of extant and extinct arachnids under a diverse regime of analytical conditions, most of which resulted in placing Uraraneida as the sister clade of Araneae (spiders). The phylogenetic placement of this arachnid fossil extends the presence of spinnerets and modified palps more basally in the arachnid tree than was previously thought. Ecologically, the new fossil extends the record of Uraraneida 170 million years towards the present, thus showing that uraraneids and spiders co-existed for a large fraction of their evolutionary history.
理解蛛形纲目之间的系统发育关系是一项艰巨的任务，但化石为确定蛛形纲生命之树的一些分支提供了依据。古生代化石的发现，其特征既存在于现存的蜘蛛中，也存在于其他蛛形纲动物中，为一系列被认为是一个等级的灭绝提供了证据，即 Uraraneida，这导致了现代蜘蛛的出现。在这里，我们报告了两个保存异常完好的中生代 Uraraneida 成员，它们具有分段的腹部、具有明确喷口的多关节纺器、改良的雄性触肢、类似蜘蛛的螯肢和类似尾骨的尾突。这些新化石属于 Chimerarachne yingi 物种，在一个包含现存和已灭绝蛛形纲动物的大型数据矩阵中，根据多种分析条件进行了系统发育分析，其中大多数结果表明 Uraraneida 是 Araneae（蜘蛛）的姐妹群。这种蛛形纲化石的系统发育位置将纺器和改良的触肢在蛛形纲动物树中的位置比以前认为的更加基础。从生态学角度来看，新化石将 Uraraneida 的记录延长了 1.7 亿年，表明 uraraneids 和蜘蛛在其进化历史的很大一部分时间里共存。
