J Syst Evol

• Research Articles •    

A unique record of Cercis from the late early Miocene of interior Asia and its significance for paleoenvironments and paleophytogeography

Xiang‐Chuan Li1,2,3* , Steven R. Manchester3 , Qin Wang1 , Liang Xiao1,2, Tian‐Long Qi1 , Yun‐Zhi Yao4 , Dong Ren4 , and Qiang Yang5   

  1. 1 College of Earth Sciences and Resources, Chang'an University, Xi'an 710054, China
    2 State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
    3 Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA
    4 College of Life Sciences, Capital Normal University, Beijing 100048, China
    5 School of Life Sciences, Guangzhou University, Guangzhou 510006, China
  • Received:2020-03-20 Accepted:2020-05-14 Online:2020-05-21

Abstract:

The climatic impacts of the Tibetan Plateau since the Neogene and the phytogeographic pattern changes of formerly widely‐distributed forest communities on the plateau remain poorly constrained. Today, Cercis L. (Fabaceae) is a well‐known arborescent genus typically distributed in subtropical to warm temperate zones of the Northern Hemisphere, and Paleogene fossil occurrences from Eurasia and North America show a long history of the genus in mid‐low latitudes of the Northern Hemisphere. Here, we describe a fossil species, Cercis zekuensis sp. nov. based on well‐preserved fruits from the early Miocene of the northeastern Tibetan Plateau. Detailed morphological comparison (e.g., ventral margin with a veinless wing) of extant and fossil members of Cercis and other genera confirmed validity of the present taxonomic identity. Based on the comparison with extant relatives and their climate preferences, this unexpected occurrence of thermophilic Cercis in northeastern Tibetan Plateau indicates this area had higher temperature and precipitation in the Miocene than today. Integrated with inferred (paleo‐)temperature lapse rates, this indicates a low paleoelevation of less than 2.4 km. In contrast with the present‐day alpine climate here (~3.7 km), such a low elevation facilitated a more favorable habitat with comparatively high biodiversity and warm temperate forests at that time, as were evidenced by co‐occurring megafossils. Moreover, the present existence of Cercis implies the genus was widespread in interior Asia during the early Neogene and shows its modern disjunction or diversification between eastern and central Asia was possibly shaped by the late Cenozoic regional tectonic uplift and consequential environmental deterioration.

Key words: Cercis, early Miocene, fossil legume, northeast Tibetan Plateau, paleoenvironment, phytogeographical pattern