New multicellular marine macroalgae from the early Tonian of northwestern Canada
New multicellular marine macroalgae from the early Tonian of northwestern Canada
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DOI：
10.1130/g48508.1
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发表时间：
2021-03-22
期刊：
影响因子：
5.8
通讯作者：
Laflamme, Marc
中科院分区：
文献类型：
--
作者：
Maloney, Katie M.;Halverson, Galen P.;Laflamme, Marc
分子系统发育数据表明，光合真核生物首先在淡水环境中演化的早元古代和多样化到海洋环境中的托尼时期，但早期的藻类进化是反映在化石记录。在这里，我们报告新发现的，毫米至厘米级的大型化石从外大陆架海相的CA。950-900 Ma（Re-Os最小年龄约束= 898 +/- 68 Ma）加拿大西北部Wernecke山脉Dolores Creek组。这些化石被氧化铁和粘土矿物包裹着，代表了两个大小级别。较大的形式功能unbranched叶状体均匀的细胞，分化的细胞壁，纵向条纹，和可能的holdfasts，而较小的标本显示分支，但没有其他诊断功能。虽然较小的人口仍然未解决的遗传学和可能代表蓝藻，我们解释了较大的化石多细胞真核大型藻类与合理的绿色藻类的亲和力的基础上，他们的大尺寸和存在的肋状壁的附着。考虑到这一点，后者是为数不多的绿色藻类和一些最大的宏观真核生物尚未确认在新元古代早期。多洛雷斯溪的化石与其他托尼阶化石一起表明，真核藻类，包括绿色藻类，在新元古代早期就定居在海洋环境中。
Molecular phylogenetic data suggest that photosynthetic eukaryotes first evolved in freshwater environments in the early Proterozoic and diversified into marine environments by the Tonian Period, but early algal evolution is poorly reflected in the fossil record. Here, we report newly discovered, millimeter- to centimeter-scale macrofossils from outershelf marine facies of the ca. 950-900 Ma (Re-Os minimum age constraint = 898 +/- 68 Ma) Dolores Creek Formation in the Wernecke Mountains, northwestern Canada. These fossils, variably preserved by iron oxides and clay minerals, represent two size classes. The larger forms feature unbranching thalli with uniform cells, differentiated cell walls, longitudinal striations, and probable holdfasts, whereas the smaller specimens display branching but no other diagnostic features. While the smaller population remains unresolved phylogenetically and may represent cyanobacteria, we interpret the larger fossils as multicellular eukaryotic macroalgae with a plausible green algal affinity based on their large size and presence of rib-like wall ornamentation. Considered as such, the latter are among the few green algae and some of the largest macroscopic eukaryotes yet recognized in the early Neoproterozoic. Together with other Tonian fossils, the Dolores Creek fossils indicate that eukaryotic algae, including green algae, colonized marine environments by the early Neoproterozoic Era.