The Oligocene Equisetum from Qaidam Basin, Northeastern Tibetan Plateau in China and its implications

ABSTRACT

Equisetum: (Equisetaceae, Equisetales) is widely distributed around the world and distinguished by obviously jointed stems with longitudinal ridges or furrows. Recently, fossil materials collected from the Shangganchaigou Formation of northwestern Qaidam Basin, China, are assigned to Equisetum based on the presence of jointed stems, longitudinal ridges, and whorls of branch scars. The current specimens are the first discovery of Equisetum in northern Tibetan Plateau and also represent the first fossil record of the genus from Oligocene in Qaidam Basin. The new discovery enriches the knowledge of the paleo-diversity of the Equisetum and indicates that the sphenophytes once existed in the northern Tibetan Plateau. Based on the fossil records in and around the Tibetan Plateau, Equisetum could survive at a higher latitude during the Palaeogene and they could only grow in lower latitude since the Neogene, which might be the result of the tectonic deformation and climatic changes in the northern plateau since the Miocene. The current fossil, together with co-existed fossils, indicate that there have been rich drainages and temperate deciduous broad-leaved forest with grass in northwestern Qaidam Basin during the Oligocene.

KEYWORDS:

• Equisetum
• Oligocene
• Qaidam Basin
• paleoenvironment
• fossil records
• Tibetan Plateau

Acknowledgments

We thank Prof. Bainian Sun (Lanzhou University, China) for the valuable advice in fossil identification and Prof. Jingyu Wu (Lanzhou University, China) for helpful suggestions. We are also grateful to the editor for their constructive comments.

Hightlights

• First fossil records of Equisetum from Oligocene in Qaidam Basin.

• Fossil records enrich the knowledge to the Cenozoic flora in the Qaidam Basin.

Disclosure statement

The authors declare that they have no conflict of interest.

Additional information

Funding

This research was supported by Second Tibetan Plateau Scientific Expedition and Research Program under Grant [number 2019QZKK0704]; [Strategic Priority Research Program (B) of the Chinese Academy of Sciences] under Grant [number XDB26000000]; and [National Natural Science Foundation of China] under Grant [numbers 41972008 and 41272026].