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.

One sample of lithic wacke (PM90TW13) from bed-13 of section PM90 was collected for detrital zircon dating. Zircon grains were separated using conventional heavy liquid and magnetic techniques at the Laboratory of Hebei Institute of Regional Geology and Mineral Resources Survey, then were mounted in epoxy and polished for cathodoluminescence (CL) imaging at the Inner Mongolia Key Laboratory of Magmatic Mineralization and Ore-prospecting (IMLM), China. Zircon U-Pb dating was conducted by using Laser ablation-Multicollector-Inductively coupled plasma-Mass spectrometry (LA-MC-ICP-MS) at IMLM. The zircon standard GJ-1 was used to calibrate U-Th-Pb ratios. Spot size for data collection was 30 μm. Off-line inspection and integration of background and analysis signals, and time-drift correction and quantitative calibration for trace element analyses and U-Pb dating were performed by using ICP-MS DataCal (Liu et al., 2008). The errors for individual U-Pb analyses are presented with 1σ error and uncertainties in grouped ages are quoted at the 90% level (1σ). Age calculation and harmonic plot drawing were completed by Isoplot 3.0 (Ludwig, 2003). Further detailed descriptions of the instrumentation and analytical procedure for the LA-MC-ICP-MS zircon U-Pb can be found in Hou et al. (2009).

Detrital zircon U-Pb dating of a sample from bed-13 at the section PM90, Dalai Sumu Town, northern Sonid Zuoqi, Inner Mongolia, China.