腕足动物小嘴贝类Axiodeaneia属在广西的发现及意义

DISCOVERY AND SIGNIFICANCE OF THE RHYNCHONELLID BRACHIOPOD AXIODEANEIA CLARK FROM GUANGXI,CHINA

文中描述了分别采自广西田东陇合屯剖面杜内阶底部和桂林南边村剖面法门阶顶部的Axiodeaneia属的两个种:Axiodeaneia cf.anxia Havlicek,1979和Axiodeaneia xuisp.nov.。前者以壳体侧边缘略内凹和壳体较宽为特征,而后者以其独特的壳褶分布形式为特征,不同于该属的其他种类。该属分子在广西的发现不仅表明华南地区在法门期晚期至杜内期时期与北美和欧洲等地存在密切的生物地理区系联系,也将Axiodeaneia属的出现时代提早到晚泥盆世法门期。同时,Axiodeaneia xuisp.nov.作为Axiodeaneia和Goniophoria两属之间的形态过渡类型,也为探讨两属的亲缘关系提供了重要线索。

Axiodeaneia is a rare genus of rhynchonellid brachiopods,initially established by Clark in 1917.It belongs to the subfamily Axiodeaneiinae of the family Rhynchotetradidae and previously included four species,namely Axiodeaneia platypleura Clark,1917,A.anxia Havlicek,1979,A.usheri（Brown,1952）, and A.glenparkensis Carter,1988.Since most species of this genus was recorded initially from Tournaisian（basal Carboniferous） deposits of North America,with one exception from Europe,this genus was long considered to be an endemic element of the early Carboniferous brachiopod faunas of North America.In this paper,two species are described from Guangxi in southern China,Axiodeaneia cf.anxia Havlicek,1979 collected from the lower Tournaisian of the Longzao Section of Tiandong County,and A.xui sp.nov.from the uppermost Fammenian（Late Devonian） of the Nanbiancun Section of Guilin.The discovery of these two species in Guangxi indicates that the brachiopod fauna of the late Fammenian to Tournaisian in South China had a close biogeographic relationship with that of North America and Europe and also records an earlier stratigraphic range of the genus,in the Fammenian of Late Devonian.The new species Axiodeaneia xui also provides an important clue to the relationship between Axiodeaneia and Goniophoria,because it is a morphologically intermediate between the two genera.Axiodeaneia xui sp.nov.,or a similar form having an unsupported sessile septalium in the form of slightly converging dental plates, may be a forerunner of Goniophoria,in which development of a ventral median septum supporting the septalium can be observed.