Winged fruits and associated leaves of Shorea (Dipterocarpaceae) from the Late Eocene of South China

来源 :广东省植物学会2012年年会 | 被引量 : 0次 | 上传用户:barbaraxj
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  As a member of the order Malvales,Dipterocarpaceae is widely considered the representative component of tropical Asian rainforests and investigated extensively because of its economic and ecological significance (Dayanandan et al.,1999).This family is currently distributed mainly in the Asian tropics (92%),dominating the canopy of tropical lowland forests and a small proportion (8%) growing in the tropics of Africa and South America (Zhang and Wang,1985).In China,12 species representing 5 genera occur in Yunnan,Guangxi,Hainan,and Xizang (Li et al.,2000).Shorea is the most diversified genus of Dipterocarpaceae and includes approximately 194 species distributed in Ceylon,India,Burma,Thailand,Indochina,and Malesia (Ashton,1982).In China,only 2 species are confined in western Yunnan and southeastern Xizang (Li et al.,2000).Fossil Shorea leaves have been described from the Tertiary of India and reliable fossil woods are well documented in the Tertiary of India and Southeast Asia (Bande and Srivastava,1990; Antal and Awasthi,1993; Konomatsu and Awasthi,1999; Gregory et al.,2009).On the contrary,convincing reproductive remnants are rare and,to date,only two authenticated Shorea winged fruits have been described from the Miocene of India (Khan and Bera,2010; Shukla et al.,2012).The winged fruits and associated leaves under study were recovered from the Late Eocene Huangniuling Formation,Maoming Basin,Guangdong province.Morphological features include: (1) fruit body spherical to ellipsoidal; three longer and two shorter persistent sepal lobes originating from the apex of the fruit body; the longer lobe elliptic to obovate,the apex rounded or obtuse,the margin entire,a total of 9-18 moderate primary veins arising from the lobe base and radiating to margin and apex; the short lobe narrow and short,9 primary veins running parallel to each other; (2) lamina elliptic to ovate,base obtuse to rounded,apex obtuse to convex,margin entire; venation pinnate; secondary veins eucamptodromous; intersecondary veins present apically; tertiary veins mixed opposite and alternate percurrent.Based on number of longer and short lobes,fruit dimension and venation of the lobe,this Maoming winged fruits show the greatest similarity to extant Shorea sericea but differ from it in the shape of the lobe apex and number of primary veins of the sepal lobe.Therefore,a new species,Shorea maomingensis sp.nov.,is established.The associated leaves resemble extant Shorea altasa in morphology and are treated as Shorea sp.Although the fruits and leaves were not preserved together,they are probably conspecific.This occurrence is the first fossil record of Shorea in China,indicating that dipterocarps had dispersed to tropical and humid South China by the Late Eocene.Except the tropical moist equatorial environment in Malesia,dipterocarps exhibit wide range of physiological tolerance for climate,which is suggested by the extensive distribution in the monsoon forests of Late Oligocene and Early Miocene Sunda region and many extant populations occurrence in the seasonally dry and even savannah climate (Morley,2000).Deciduous oaks (Quercus conferta Boitz.,Q.forestdalensis Trav.) pollen grains became common in the Huangniuling Formation,reflecting the increase of aridity and seasonality from the Late Eocene.Based on this,we suppose that dipterocarps probably got adapted to this seasonal climate from the Late Eocene to Early Miocene,expanded northward in the Middle Miocene climatic optimum,and declined and gradually disappeared from the southeastern part of the continent from the Late Miocene.
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