A Silurian pseudocolonial pterobranch
A Silurian pseudocolonial pterobranch
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DOI：
10.1016/j.cub.2023.10.024
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发表时间：
2023-12-04
期刊：
影响因子：
9.2
通讯作者：
Koch，Nicolas Mongiardino
中科院分区：
文献类型：
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作者：
Briggs，Derek E. G.;Koch，Nicolas Mongiardino
翼鳃类是半索动物门的一个主要类群，最早出现在寒武纪的化石记录中1，有600多个化石属，以古生代的浮游笔石为主，广泛用作对比沉积岩序列的带状化石。2翼鳃类现今已很少见；它们是无柄的海洋形态，以横纹石（被认为是唯一活着的笔石）和头盘石为代表。与它们的姊妹类群笔石不同，头盘类是假殖民性的。3,4在这里，我们描述了来自安大略省志留纪（普里多利）伯蒂群（420 mya）的一个有问题的化石，这是一系列近岸沉积物，以其显着保存的广翅类（海蝎）多样性而闻名。5该化石，Rotaciurca superbus，一个新的属和新种，是众所周知的作为以西结的轮子，5参考了组成它的管子的不寻常的圆形排列。管的结构和排列将轮形鱼确定为翼目，系统发育分析将其与头盘类分类。我们将其归入一个新科 Rotaciurcidae 中，以将其与 Cephalodiscidae 区分开来。与管子相关的大型结构被解释为漂浮物，这将 Rotaciurca 区分为唯一已知的浮游头盘类动物，因此头盘类动物像笔石一样侵入了水柱。这种生活方式反映了浮游海洋群落中伪群落大型无脊椎动物的稀有性，而这一角色由今天被称为樽海鞘的被囊动物（脊索动物）占据。我们对分歧时间的估计，第一次使用宽松的全证据时钟，将半索动物和翼鳃类的起源追溯到最早的寒武纪（福图尼亚）。
Pterobranchs, a major group of the phylum Hemichordata, first appear in the fossil record during the Cambrian,1and there are more than 600 fossil genera dominated by the mainly planktic graptolites of the Paleozoic, which are widely used as zone fossils for correlating sedimentary rock sequences.2Pterobranchs are rare today; they are sessile marine forms represented byRhabdopleura, which is considered the only living graptolite, andCephalodiscus. Unlike their sister taxon, the colonial graptolites, cephalodiscids are pseudocolonial.3,4Here, we describe a problematic fossil from the Silurian (Pridoli) Bertie Group of Ontario (420 mya), a sequence of near-shore sediments well known for its remarkably preserved diversity of eurypterids (sea scorpions).5The fossil,Rotaciurca superbus, a new genus and species, was familiarly known as Ezekiel's Wheel,5with reference to the unusual circular arrangement of the tubes that compose it. The structure and arrangement of the tubes identifyRotaciurcaas a pterobranch, and phylogenetic analysis groups it with the cephalodiscids. We place it in a new family Rotaciurcidae to distinguish it from Cephalodiscidae. A large structure associated with the tubes is interpreted as a float, which would distinguishRotaciurcaas the only known planktic cephalodiscid—thus cephalodiscids, like the graptolites, invaded the water column. This mode of life reflects the rarity of pseudocolonial macroinvertebrates in planktic ocean communities, a role occupied by the tunicates (Chordata) known as salps today. Our estimates of divergence times, the first using relaxed total-evidence clocks, date the origins of both hemichordates and pterobranchs to the earliest Cambrian (Fortunian).