Exploring the Formation of a Disjunctive Pattern between Eastern Asia and North America Based on Fossil Evidence from Thuja (Cupressaceae)

Jian Yang,David Kay Ferguson,Bin Sun,Qing-Wen Ma,Cheng-Sen Li,Yu-Fei Wang,Navnith K.P Kumaran,Hai-Feng Wang,Yi-Ming Cui

doi:10.1371/journal.pone.0138544

Abstract

Thuja, a genus of Cupressaceae comprising five extant species, presently occurs in both East Asia (3 species) and North America (2 species) and has a long fossil record from Paleocene to Pleistocene in the Northern Hemisphere. Two distinct hypotheses have been proposed to account for the origin and present distribution of this genus. Here we recognize and describe T. sutchuenensis Franch., a new fossil Thuja from the late Pliocene sediments of Zhangcun, Shanxi, North China, based on detailed comparisons with all living species and other fossil ones, integrate the global fossil records of this genus plotted in a set of paleomaps from different time intervals, which show that Thuja probably first appeared at high latitudes of North America in or before the Paleocene. This genus reached Greenland in the Paleocene, then arrived in eastern Asia in the Miocene via the land connection between East Asia and western North America. In the late Pliocene, it migrated into the interior of China. With the Quaternary cooling and drying, Thuja gradually retreated southwards to form today’s disjunctive distribution between East Asia and North America.

Highlights

Disjunct distribution between eastern Asia and North America is a widespread phenomenon in the Northern Hemisphere
Thuja fossils have been widely found in sediments of Paleocene to Pleistocene age in the Northern Hemisphere from 36.8°N to 86.3°N [34,35,36,37,38,39,40,41,42,43,44,45] (Fig 6)
In the Paleocene as the Atlantic Ocean gradually expanded, North America, Greenland and Eurasia remained connected at high latitudes

Summary

Introduction

Disjunct distribution between eastern Asia and North America is a widespread phenomenon in the Northern Hemisphere. It represents one of Thorne’s 14 types of disjunct distribution [1]. In 1750 Linnaeus and his student Jonas P. Halenius discovered that the flora of eastern Asia and eastern North America displayed similarities [2, 3]. In the 19th Century Asa Gray compared the flora of North America and Japan, and further described the details of the disjunctive distribution pattern in eastern Asia and North America [4,5,6,7,8,9]. Gray’s studies encouraged many subsequent scientists to study the phenomenon of disjunctive distribution in different fields

Methods

Results

Conclusion