Jaw elements in Plumulites bengtsoni confirm that machaeridians are extinct armoured scaleworms
Jaw elements in Plumulites bengtsoni confirm that machaeridians are extinct armoured scaleworms
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DOI：
10.1098/rspb.2019.1247
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发表时间：
2019-07-24
影响因子：
4.7
通讯作者：
Vinther, Jakob
中科院分区：
文献类型：
--
作者：
Parry, Luke A.;Edgecombe, Gregory D.;Vinther, Jakob
马凯里迪亚人是一种古生代动物，其背部覆盖着覆盖或包裹身体的序列化、叠瓦状壳板。在发现来自摩洛哥早奥陶世的一个有关节的plumulitid machaeridian之前，它保留了明确的环节动物特征（带有毛的节段副足），machaeridian是一个古生物学上的谜团，以前与棘皮动物，藤壶，tommotiids（假定的茎组腕足动物）或软体动物有关。虽然现在已经确定了Machaeridians的环节动物亲缘关系，但它们在门内的位置和理解环节动物早期进化的相关性并不那么安全，与竞争的假设将Machaeridia放在船尾或深深嵌套在环节动物的冠群中。我们描述了从摩洛哥的Fezouata组的Plumulites bengtsoni的scleritome，保留了前颚装置组成的至少两个离散的元素，表现出生长线。虽然颚有多个独立的起源环节动物的冠组，可比的颚只存在于Phyllodocida，林间空地，包含现代aphroditiforms（scaleworms和亲戚）。系统发育分析的地方单系Machaeridia内冠组Phyllodocida总组Aphroditiformia，符合一个共同的起源Machaeridian壳板和scaleworm elytrae。在Aphroditiformia中包含Machaeridians使Phyllodocida的幽灵谱系缩短了近一亿年。
Machaeridians are Palaeozoic animals that are dorsally armoured with serialized, imbricating shell plates that cover or enclose the body. Prior to the discovery of an articulated plumulitid machaeridian from the Early Ordovician of Morocco that preserved unambiguous annelid characters (segmental parapodia with chaetae), machaeridians were a palaeontological mystery, having been previously linked to echinoderms, barnacles, tommotiids (putative stem-group brachiopods) or molluscs. Although the annelid affinities of machaeridians are now firmly established, their position within the phylum and relevance for understanding the early evolution of Annelida is less secure, with competing hypotheses placing Machaeridia in the stern or deeply nested within the crown group of annelids. We describe a scleritome of Plumulites bengtsoni from the Fezouata Formation of Morocco that preserves an anterior jaw apparatus consisting of at least two discrete elements that exhibit growth lines. Although jaws have multiple independent origins within the annelid crown group, comparable jaws are present only within Phyllodocida, the Glade that contains modern aphroditiforms (scaleworms and relatives). Phylogenetic analysis places a monophyletic Machaeridia within the crown group of Phyllodocida in total-group Aphroditiformia, consistent with a common origin of machaeridian shell plates and scaleworm elytrae. The inclusion of machaeridians in Aphroditiformia truncates the ghost lineage of Phyllodocida by almost a hundred million years.