Moreau Jean-David, Philippe Marc, Néraudeau Didier, Dépré Eric, Le Couls Matthieu, Fernandez Vincent, Beurel Simon
Biogéosciences, UMR CNRS 6282, Université de Bourgogne Franche-Comté, 6 boulevard Gabriel, Dijon, 21000, France.
Université de Lyon, Claude-Bernard Lyon-1, ENTPE, CNRS, UMR 5023 LEHNA, Villeurbanne, 69622, France.
Am J Bot. 2021 Sep;108(9):1745-1760. doi: 10.1002/ajb2.1722. Epub 2021 Sep 8.
The conifer Geinitzia reichenbachii was a common member of the Cretaceous Laurasian floras. However, the histology of G. reichenbachii leafy axes was never described in detail, and our knowledge of its paleoecology remains very limited. Using new and exquisitely preserved silicified material from the Upper Cretaceous of western France, we describe G. reichenbachii from the gross morphology to the cellular scale, then discuss paleoecological and taphonomical implications.
We examined specimens from two localities in western France (Claix and Moragne) using propagation phase-contrast X-ray synchrotron microtomography.
The cuticle and the inner tissues of leafy axes are preserved in three dimensions. Epidermis, hypodermis, palisade parenchyma, spongy parenchyma, transfusion tracheids, and most of tissues of the vascular cylinder are clearly discernible. The numerous resin ducts are sometimes filled by persisting resin. Additionally, surfaces of some leaves preserved drops and flows of resin.
Depositional environmental context combined with histological features of G. reichenbachii suggest that this conifer was adapted to a range of marginal-littoral ecosystems including those open to the sea paleoenvironments and innermost ones influenced by strong continental inputs. Geinitzia reichenbachii was adapted to withstand intense sunlight, hot temperatures coupled with salty sea wind, and dry conditions. The frequent amber-bearing beds in the Cretaceous from western France with Geinitzia as a main component of the associated floras raises the possibility of a role for Geinitzia in the production of the "Charentese amber".
松柏类植物赖兴巴赫盖尼兹杉是白垩纪劳亚植物群的常见成员。然而，赖兴巴赫盖尼兹杉叶轴的组织学从未被详细描述过，我们对其古生态学的了解仍然非常有限。利用来自法国西部上白垩统的新的、保存精美的硅化材料，我们从宏观形态到细胞尺度描述了赖兴巴赫盖尼兹杉，然后讨论了其古生态学和埋藏学意义。
我们使用传播相衬X射线同步加速器显微断层扫描技术检查了来自法国西部两个地点（克莱克斯和莫拉涅）的标本。
叶轴的角质层和内部组织在三维空间中得以保存。表皮、皮下组织、栅栏薄壁组织、海绵薄壁组织、输导管胞以及维管束的大部分组织都清晰可辨。众多的树脂道有时被残留的树脂填充。此外，一些叶子表面保存着树脂滴和树脂流。
沉积环境背景与赖兴巴赫盖尼兹杉的组织学特征表明，这种针叶树适应了一系列边缘滨海生态系统，包括那些面向海洋古环境的生态系统以及受强烈陆源输入影响的最内陆生态系统。赖兴巴赫盖尼兹杉能够适应强烈的阳光、高温以及咸海风和干燥条件。法国西部白垩纪频繁出现的含琥珀层，其中赖兴巴赫盖尼兹杉是相关植物群的主要组成部分，这增加了赖兴巴赫盖尼兹杉在“夏朗德琥珀”形成过程中发挥作用的可能性。
