Heteropolar eunotioid diatoms (Bacillariophyceae) were common in the North American Arctic during the middle Eocene
Heteropolar eunotioid diatoms (Bacillariophyceae) were common in the North American Arctic during the middle Eocene
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始新世中期，异极真硅藻（Bacillariophyceae）在北美北极地区很常见
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
A. P. Wolfe
中科院分区：
文献类型：
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作者：
P. Siver;J. Bishop;Anne M. Lott;A. P. Wolfe
齿状硅藻在顶轴和跨顶轴上都表现出不对称性，形成异极瓣膜，通常被归入放线菌属。不同物种的杂极程度不同，从两极之间的细微差异到具有顶端突起的高度分化的头极。极间差异较小且缺乏顶端突起的放线菌种类与Euntia同级。据报道，全球已知物种超过100种，主要分布在热带地区，目前只有斑点放线菌刘易斯，1864在北美已知。作为对加拿大北部北极圈附近始新世中期长颈鹿陨石坑的生物调查和清查项目的一部分，我们发现了大量的真硅藻，其中至少有5种属于放线菌，其中3种在本文中被正式描述为A.hickeyi sp.。Nov.、古氏曲霉A.gowinii sp.11月和金伯利冰草A.kimberlitica sp.11月..这些硅藻都缺乏顶端突起，与Euntia中现代的异极硅藻相似。这项贡献的目的是报告长颈鹿地区相对于现代和化石的裸藻分类群的发现，讨论使用杂极作为放线菌属的区别特征，并考虑这些观察到的古气候和生物地理意义。
Eunotioid diatoms that express asymmetry in both the apical and transapical axes, forming heteropolar valves, are generally placed in the genus Actinella. The degree of heteropolarity varies between species, ranging from subtle differences between poles to highly differentiated head poles bearing an apical protuberance. Actinella species with less difference between the poles and lacking an apical protuberance are gradational with Eunotia. With over 100 known species reported globally, primarily in the tropics, only Actinella punctata Lewis, 1864 is currently known from North America. As part of a biotic survey and inventory project focused on the middle Eocene Giraffe crater locality near the Arctic Circle in northern Canada, we have uncovered a wealth of eunotioid diatoms including at least five heteropolar species attributed to Actinella, three of which are described formally herein as A. hickeyi sp. nov., A. goodwinii sp. nov. and A. kimberlitica sp. nov.. These diatoms all lack apical protuberances and bear resemblance to modern heteropolar counterparts within Eunotia. The objectives of this contribution are to report the findings from the Giraffe locality relative to modern and fossil eunotiophycid taxa, discuss the use of heteropolarity as a distinguishing character for the genus Actinella, and consider the palaeoclimatic and biogeographical implications of these observations.