Anatomically Preserved Middle Miocene Flora at Yakima Canyon, Washington State: Floristic Composition, Evolutionary, and Phytogeographic Significance

摘要：来自美国华盛顿州中部的中中新世亚基马峡谷植物群（15.6 Ma）包含了解剖学上保存下来的种子、果实和营养植物的遗骸，这在北美新近纪中是非常罕见的。这些化石提供了从更普遍保存的新近纪叶片压缩区系中无法获得的分类、进化和植物地理数据。根据形态和解剖特征，植物可以在不同的属内分类水平上被识别，包括：一种松树，Pinus foisyi，可归属于Oocarpae分节，其中包括现存的加利福尼亚闭锥松；栎科栎属黑栎，橡子发育特征与现代白栎树十分相似；一种甜桉树，类似于几种现代的桉树科，在丝状蕨类植物中，本质上是现代的伍德沃德属，可能归属于现代弗吉尼亚链蕨W. virginica和Osmunda wehrii，属于现代的Osmunda亚属。这些植物代表了混合叶生植物林达到其最大地理分布的时间间隔，并且在可能是新近纪最温暖的时间间隔中生长。在某些情况下，它们代表了广泛而多样的温带植物群的“最后一站”，而今天，这些植物群的代表是亚洲/北美东部不间断分布的植物。进一步的研究将以解剖学上保存的化石遗骸和几个已灭绝的中新世属的存在为基础，对第一个温带中新世植物区系进行概述。

ABSTRACT9980388PiggThe middle Miocene Yakima Canyon flora (15.6 Ma) from central Washington state contains anatomically preserved seed, fruit and vegetative plant remains that are quite rarely preserved in the Neogene of North America. These fossils provide taxonomic, evolutionary and phytogeographic data impossible to obtain from the more commonly preserved Neogene leaf compression floras. Based on morphological and anatomical features, plants can be recognized at varying infrageneric taxonomic levels including: a pine, Pinus foisyi, assignable to Subsection Oocarpae, which includes extant California closed cone pines; an oak, Quercus hiholensis of Section Quercus, with acorn developmental features quite similar to those of modern white oaks; a sweet gum, Liquidambar, similar to several modern species of Section Liquidambar, and, among the filicalean ferns, essentially modern Woodwardia, probably assignable to the modern Virginia chain fern W. virginica, and Osmunda wehrii, which fits within the modern Subgenus Osmunda. These plants represent the time interval when the mixed mesophytic forest reached its maximum geographic distribution and grew during what was possibly the warmest interval in the Neogene. In some cases, they represent the "last stand" of a widespread, diverse temperate flora that today is represented by plants with a disjunct Asian/eastern North American distribution. Further study will document an overview of the first temperate middle Miocene flora to be based on anatomically preserved fossil remains, and the presence of several extinct Miocene genera.