Re-description of the Spence Shale palaeoscolecids in light of new morphological features with comments on palaeoscolecid taxonomy and taphonomy
Re-description of the Spence Shale palaeoscolecids in light of new morphological features with comments on palaeoscolecid taxonomy and taphonomy
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DOI：
10.1007/s12542-020-00516-9
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发表时间：
2020-02
期刊：
影响因子：
1.8
通讯作者：
A. Whitaker;Paul G. Jamison;J. Schiffbauer;J. Kimmig
中科院分区：
文献类型：
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作者：
A. Whitaker;Paul G. Jamison;J. Schiffbauer;J. Kimmig
犹他州和爱达荷州的中寒武世(苗林系；乌连期)Spence页岩保存了生物矿化和软体生物群的多样化组合。这种动物群中最稀有的标本是古鞭毛虫。直到最近，从Spence页岩中只发现了一个标本，这是1969年的Palaeoscolex ratclffeiRobison的正型标本，后来被归入Wronascolex属。该标本作为部分和对应物保存下来，但缺失了后端和前端。莱利·史密斯发现了一种新标本，它保存了一根有刺的外翻鼻子。根据扫描电子显微镜和能量色散X射线能谱(SEM-EDS)和光学显微镜收集的新数据，该种被认为代表了一新属，犹他科尔克斯根(Utahscolexgen)。Nov.，而不是先前提出的一种古鞭毛虫或Wronas Colexas。新属与其他两属的不同之处在于没有节状纹饰，也没有微板和小片。在此案例研究的基础上，建议未来修订的古脊椎动物分类学需要了解板、血小板和微板的装饰，以及板、血小板和微板在角质层上的排列。除了新标本提供的改进的形态信息外，它还促进了我们对Spence页岩和古颈椎蠕虫的攻丝途径的了解。本种的两个标本的盘的保存在元素组成上不同，在质量上有点不同。虽然正型和新的样品都显示出镁和磷在板内的局部化，但正型的样品含有大量的铁成分，而新的样品相反地显示出钙的升高。此外，整个样品中可以观察到干酪根化、黄铁矿化、铝硅化和磷化。不仅标本之间的保存情况不同，而且标本内部的保存情况也不同，这表明了Burgess页岩型矿床中保存路径的高度多样性，并提供了对导致Spence页岩中软体保存的情况的洞察。
The middle Cambrian (Miaolingian Series; Wuliuan Stage) Spence Shale of Utah and Idaho preserves a diverse assemblage of biomineralized and soft-bodied taxa. Among the rarest specimens of this fauna are palaeoscolecid worms. Until recently, only one specimen was known from the Spence Shale, the holotype specimen ofPalaeoscolex ratcliffeiRobison, 1969, later included in the genusWronascolex.This specimen is preserved as part and counterpart but missing both the posterior and anterior terminations. A new specimen, discovered by Riley Smith, preserves an everted proboscis with spines. Based on new data collected using scanning electron microscopy and energy dispersive X-ray spectrometry (SEM–EDS), and optical microscopy, the species is thought to represent a new genus,Utahscolexgen. nov., rather than a species ofPalaeoscolexorWronascolexas previously suggested. The new genus differs from the other two genera in the lack of node ornamentation of the plates, as well as the absence of microplates and platelets. Based on this case study, it is recommended that future revisions of palaeoscolecid taxonomy require knowledge of plate, platelet, and microplate ornamentation, as well as the arrangement of the plates, platelets, and microplates on the cuticle. In addition to the improved morphological information provided by the new specimen, it also advances our knowledge of the taphonomic pathways in the Spence Shale and in palaeoscolecid worms in general. The preservation of the plates of the two specimens of this species differ in elemental composition and somewhat in quality. While both the holotype and new specimen show localized magnesium and phosphorus within the plates, the holotype has a substantial iron component, whereas the new specimen instead shows elevated calcium. In addition, kerogenization, pyritization, aluminosilicification, and phosphatization can be observed throughout the specimen. The preservation varies not only between the specimens, but also within, demonstrating the high variability of preservational pathways within a Burgess Shale-type deposit, and providing insights into the circumstances that lead to soft-bodied preservation in the Spence Shale.