A new species of Nilssoniopteris (Bennettitales) from the Lower Cretaceous Jianchang Basin, western Liaoning, NE China

The Bennettitales were a prevalent Mesozoic plant group that became extinct at the end of the Cretaceous. Nilssoniopteris, an important bennettitalean genus, differs from other fossil genera and extant cycads by its entire pinnate leaves and syndetocheilic stomata with sinuous cell walls. First described by Nathorst (1909) from the Middle Jurassic of Yorkshire, the genus, was distributed mainly across mid‑latitude regions of Eurasia and North America from the Late Triassic to the Early Cretaceous, and is generally considered an indicator of warm, humid climates. Here we report a new fossil species, Nilssoniopteris macrophylla sp. nov., from the Lower Cretaceous Binggou Formation of the Jianchang Basin, western Liaoning, China. This specimen represents the largest known leaf of the genus to date. We describe its macroscopic morphology and epidermal structure in detail. Together with the co‑occurring species N. binggouensis Na et al., this discovery marks the easternmost distribution of the genus in Eurasia. A compilation of global occurrences of Nilssoniopteris reveals a pronounced northward migration from the Triassic to the Cretaceous, culminating in its appearance at mid‑to-high paleolatitudes during the Albian. The leaf size and entire margin of N. macrophylla are consistent with warm, frost‑free, and humid climatic conditions that prevailed during the late Albian. The occurrence of this species at 106.5±1.9 Ma, falling within the OAE 1b–c interval, provides terrestrial evidence that the greenhouse warming associated with these oceanic anoxic events also affected continental ecosystems in Northeast China, enabling thermophilic plants to expand into higher latitudes.