Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania, 16802, USA.
Museo Paleontológico Egidio Feruglio, Consejo Nacional de Investigaciones Científicas y Técnicas, Trelew, 9100, Chubut, Argentina.
Am J Bot. 2020 May;107(5):806-832. doi: 10.1002/ajb2.1467. Epub 2020 May 9.
Eocene floras of Patagonia document biotic response to the final separation of Gondwana. The conifer genus Araucaria, distributed worldwide during the Mesozoic, has a disjunct extant distribution between South America and Australasia. Fossils assigned to Australasian Araucaria Sect. Eutacta usually are represented by isolated organs, making diagnosis difficult. Araucaria pichileufensis E.W. Berry, from the middle Eocene Río Pichileufú (RP) site in Argentine Patagonia, was originally placed in Sect. Eutacta and later reported from the early Eocene Laguna del Hunco (LH) locality. However, the relationship of A. pichileufensis to Sect. Eutacta and the conspecificity of the Araucaria material among these Patagonian floras have not been tested using modern methods.
We review the type material of A. pichileufensis alongside large (n = 192) new fossil collections of Araucaria from LH and RP, including multi-organ preservation of leafy branches, ovuliferous complexes, and pollen cones. We use a total evidence phylogenetic analysis to analyze relationships of the fossils to Sect. Eutacta.
We describe Araucaria huncoensis sp. nov. from LH and improve the whole-plant concept for Araucaria pichileufensis from RP. The two species respectively resolve in the crown and stem of Sect. Eutacta.
Our results confirm the presence and indicate the survival of Sect. Eutacta in South America during early Antarctic separation. The exceptionally complete fossils significantly predate several molecular age estimates for crown Eutacta. The differentiation of two Araucaria species demonstrates conifer turnover during climate change and initial South American isolation from the early to middle Eocene.
巴塔哥尼亚始新世的植物群记录了生物对冈瓦纳大陆最终分裂的反应。松科南洋杉属植物在中生代广泛分布，但现在仅在南美和澳大拉西亚间断分布。通常，归入澳大拉西亚南洋杉组 Eutacta 的南洋杉化石仅以孤立的器官代表，难以诊断。来自阿根廷巴塔哥尼亚中间始新世的里皮略夫河（RP）地点的Araucaria pichileufensis E.W. Berry 最初被归入 Eutacta 组，后来在早始新世的拉古纳 del Hunco（LH）地点也有报道。然而，A. pichileufensis 与 Eutacta 组的关系以及这些巴塔哥尼亚植物群中南洋杉材料的同物异性尚未使用现代方法进行测试。
我们重新研究了 A. pichileufensis 的模式标本，同时还对来自 LH 和 RP 的大量（n = 192）新的南洋杉化石进行了研究，包括叶状枝、胚珠复合体和花粉球的多器官保存。我们使用全证据系统发育分析来分析化石与 Eutacta 组的关系。
我们描述了来自 LH 的 Araucaria huncoensis sp. nov.，并改进了来自 RP 的 A. pichileufensis 的全株概念。这两个物种分别在 Eutacta 组的冠部和茎部中解析。
我们的结果证实了在南极早期分离期间，Eutacta 组在南美存在并存活。异常完整的化石明显早于几个分子年龄估计的冠部 Eutacta。两个南洋杉物种的分化表明，在气候变化和早至中始新世南美与早期隔离期间，松柏类植物发生了更替。
