A new Late Devonian flora from Sonid Zuoqi, Inner Mongolia, northeastern China

The Silurian and Devonian plant fossil record is the basis for our understanding of the early evolution of land plants, yet our appreciation of early global phytogeographic evolution has been constrained by the focus of most studies on deposits from Europe, North America, and more recently South China. Devonian plants have been rarely recorded from northeastern China, and among previous records, few plants have been illustrated and formally described. In this article, megafossil plants representing a Late Devonian-aged (probably Famennian) flora are described from a locality at northern Sonid Zuoqi, Inner Mongolia, NE China. The flora includes Melvillipteris sonidia new species, Archaeopteris sp., and fragments of some other plants. The new plant shows main axes and two orders of lateral branches. The first-order branches of this plant show a typical zigzag appearance and are borne in pairs on main axes. Second-order branches are straight or slightly flexed, and are borne helically or alternately on first-order branches. Sterile ultimate appendages and fertile structures of M. sonidia n. sp. are borne alternately on second-order branches. An associated palynological assemblage, as well as U-Pb ages of detrital zircon grains from adjacent horizons, are also reported, indicating a Late Devonian age in accord with the megafossil plants. The present study contributes to our appreciation of the Devonian floristic diversity of the Xing’an Block, and, through our review of the record of early vascular plants from NE China, more broadly to the understanding of the mid-latitude vegetation of the Northern Hemisphere during the Late Devonian.

志留纪与泥盆纪的植物化石记录，是我们认知陆生植物早期演化的核心基础。然而，当前多数研究多聚焦于欧洲、北美以及近年的华南沉积序列，这一局限制约了我们对全球早期植物地理区系演化的全面理解。中国东北地区此前鲜有泥盆纪植物化石的报道，且已有的零星记录中，多数植物未附插图亦未完成正式分类学描述。本文记述了产自位于中国东北地区的内蒙古自治区苏尼特左旗北部某产地的晚泥盆世（大概率为法门期）植物大化石组合，该植物群包含新种苏尼特梅尔维尔蕨（Melvillipteris sonidia）、古蕨属未定种（Archaeopteris sp.）以及其他若干植物的碎片。该新种植物具有主茎与两级侧枝：一级侧枝呈典型之字形弯曲，对生于主茎；二级侧枝直或微弯曲，螺旋状或交互状着生于一级侧枝上。苏尼特梅尔维尔蕨的不育末级附属器与生殖结构均交互着生于二级侧枝之上。本文同时报道了伴生的孢粉组合，以及采自相邻层位的碎屑锆石U-Pb测年结果，二者均指示该化石组合的时代为晚泥盆世，与植物大化石的时代判定一致。本研究不仅增进了我们对兴安地块泥盆纪植物群多样性的认知，同时通过梳理中国东北地区早期维管植物化石记录，进一步深化了对晚泥盆世北半球中纬度植被的整体认识。