Museo Paleontológico Egidio Feruglio, Consejo Nacional de Investigaciones Científicas y Técnicas, Avenida Fontana 140, Trelew, Chubut, 9100, Argentina.
L. H. Bailey Hortorium, Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, New York, 14853, U.S.A.
Am J Bot. 2020 Jul;107(7):1054-1071. doi: 10.1002/ajb2.1501. Epub 2020 Jun 29.
Undoubtedly, fossils are critical for understanding evolutionary transformations in deep time. Here, we reinvestigate the microspores and megaspores of Paleoazolla patagonica, a water fern found in Late Cretaceous sediments of the Chubut Province, Patagonia, Argentina, which provides novel evidence on the past history of the water fern clade. The study was based on recently collected specimens and additional observations of the original material.
Most specimens analyzed herein were obtained from new palynological samples collected at the Cerro Bosta and Cañadón del Irupé localities, La Colonia Formation. Samples were mechanically disaggregated and treated with hydrofluoric and hydrochloric acid. Spores were studied using standard light microscopy and scanning electron microscopy. We also reexamined the original materials.
The newly described characters of Paleoazolla include the presence of heterosporangiate sori composed of one ellipsoidal megasporangium surrounded by three to four oval microsporangia, megasporangium containing one hairy massula that encloses two trilete megaspores (rarely one or three), and microsporangia containing numerous microspore massulae with non-septate multibarbed glochidia and one trilete microspore per massula.
The reinterpretation has revealed a novel set of characters for understanding the evolution of heterosporous water ferns. The presence of two megaspores in the megasporangium of Paleoazolla exposes serious gaps in the current knowledge on the evolution of monomegaspory in heterosporous water ferns, a fact that emphasizes the need of including fossils within phylogenies to elucidate patterns of character acquisition among water ferns.
化石无疑对深入了解远古时期的进化转变至关重要。在这里，我们重新研究了 Paleoazolla patagonica 的小孢子和大孢子，这是一种在阿根廷巴塔哥尼亚丘布特省晚白垩世沉积物中发现的水蕨，为水蕨类群的过去历史提供了新的证据。该研究基于最近采集的标本和对原始材料的额外观察。
本文分析的大多数标本均来自在 Cerro Bosta 和 Cañadón del Irupé 地点、La Colonia 组新采集的孢粉学样本。样品经机械分散并用氢氟酸和盐酸处理。孢子使用标准的光学显微镜和扫描电子显微镜进行研究。我们还重新检查了原始材料。
新描述的 Paleoazolla 特征包括存在异孢子囊，由一个椭圆形的大孢子囊和三到四个椭圆形的小孢子囊组成，大孢子囊内含有一个毛发状的massula，它包围着两个三裂缝大孢子（很少有一个或三个），小孢子囊内含有许多小孢子massulae，带有不分隔的多刺 glochidia 和每个 massula 中的一个三裂缝小孢子。
重新解释揭示了一套理解异孢子水蕨进化的新特征。Paleoazolla 大孢子囊中存在两个大孢子，这暴露了当前关于异孢子水蕨中单大孢子进化的知识中的严重空白，这一事实强调了在系统发育中包括化石以阐明水蕨中特征获取模式的必要性。
