Discovery of a Macrophyllous Leaf of Nilssoniopteris (Bennettitales) from the Lower Cretaceous Jianchang Basin, Western Liaoning, NE China

Bennettitales were a widespread gymnosperm group throughout the Mesozoic Era, flourishing alongside dinosaurs before ultimately becoming extinct at the end of the Cretaceous. Nilssoniopteris Nathorst represents an important genus within Bennettitales, and its unique macroscopic morphology, characterized by entire and pinnate leaves, distinguishes it from other leafy form genera of Mesozoic Bennettitales. Furthermore, like that of other bennettitalean genera, its stomatal morphology (specifically the syndetocheilic stomata and sinuate cell walls) differs significantly from that of extant cycads. This genus was initially described by Nathorst in 1909 based on materials from the Middle Jurassic of Yorkshire. It was primarily distributed across mid–latitude regions, including Eurasia and North America, from the Late Triassic to the Early Cretaceous, and is generally regarded as an indicator of a warm and humid paleoclimate. The current study reports the discovery of a new fossil species, Nilssoniopteris macrophylla sp. nov., from the Lower Cretaceous deposits of the Jianchang Basin in western Liaoning Province, China. It represents the largest known leaf of this genus discovered to date. The macroscopic morphology and epidermal structure of this specimen are described in detail. This discovery, together with another co–occurring species, N. binggouensis, indicates the easternmost record of this genus' distribution in Eurasia. Moreover, the presence of such entire–margined plants in the Binggou Formation (Albian) provides compelling evidence for extremely hot and humid climatic conditions in NE China during this period. This finding suggests that the the Oceanic Anoxic Event 1c (OAE1c) was likely approaching, and the region may have already been experiencing the associated rise in temperature. Grant Number: NSFC (Nos. U2544204, 41902009), Liaoning Provincial Department of Education Scientific Research Platform Construction Project (LJ232510166001)