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Dacrycarpus pattern shedding new light on the early floristic exchange between Asia and Australia

Xinkai Wu,Xiao-Yan Liu,T. Kodrul,C. Quan,Jianhua Jin

Published 2019 in National Science Review

ABSTRACT

The recent discovery of mummified Dacrycarpus remains from the Miocene Erzitang Formation of the Guiping Basin, Guangxi, southern China, essentially contests our concepts of floristic exchange between Australia and China. East Asia has several biodiversity hotpots and is a key region for understanding the origin and evolution of the biodiversity in the Northern Hemisphere [1]. Most Gondwanan elements in East Asia are those formerly distributed across much wide areas in the Southern Hemisphere, but their modern distributions are the results of complex geological and climatic changes. Understanding the biogeographical history of Gondwanan taxa, and the mechanism underpinning their current distributions, help in understanding and conserving extant biodiversity. Nowadays, Dacrycarpus (Endlicher) de Laubenfels (Podocarpaceae) is transequatorially distributed in the western Pacific Region, from southernmost China to Fiji and New Zealand (Fig. 1) [2]. However, this genus is considered to be of Gondwanan origin, given that almost all the known megafossils have been documented from the Southern Hemisphere, especially from Australasia and South America (Fig. 1), with the earliest records from Eocene of Patagonia and Australia [3]. Such a remarkable distributional difference between the modern and geological range suggests that Dacrycarpus is a good example of cross-equatorial migration over extremely long distances and latitudinal shifts in Gondwanan biogeography. Recently, we discovered the first Northern Hemisphere Dacrycarpus megafossil record from the Miocene Erzitang Formation of Guiping Basin, Guangxi, low-latitude southern China. The remains are preserved as whole-plant, with mummified leafy shoots with dimorphic leaves, female cones and a male cone with in situ pollen (Fig. 2; taxonomic details will be published in a separate paper). The occurrence of these fossils solidly suggests the arrival ofDacrycarpus in Asia from the Southern Hemisphere at least by theMiocene, referred to as the Dacrycarpus pattern of paleophytogeography. By reviewing the biogeographic history of this genus, we here discuss the related geological and climate events and plant physiological characteristics underpinning this migration in deep time.

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