Mutwakil Nafi
Dongola University, Sudan
Title: The descendants Clarkina of the Eurasian stock (Changhsingian) and the forms of Clarkina wangi at Ganxi, Xiakou and Tianqiao sections, South China
Biography
Biography: Mutwakil Nafi
Abstract
The descendants Clarkina of the Eurasian stock (Changhsingian) are composed of C. changxingensis, C. changxingensis yini, C. deflecta, C. guangyuanensis, C. inflecta, C. iranica, C. liangshanensis, Clarkina longicuspidata, C. meishanensis meishanensis, C. meishanensis, C. orientalis, C. parasubcarinata, C. postwangi, C. prechangxingensis and C. predeflecta, C. preiranica sp. nov., C. subcarinata (Sweet), and C. wangi. One new species of C. preiranica sp. nov. has been recognized. Clarkina preiranica sp. nov. is very important because it is found at the same level with C. wangi. The base of the Changhsingian can be defined within an evolutionary lineage from C. longicuspidata to C. wangi based on a refined taxonomic approach. There are three forms of Clarkina wangi: (1) Those forms characterized by drop-like, with a short and wide platform, usually no free blade, fused carina looks like a high wall and reaching beyond the posterior margin., (2) Those forms characterized by a free blade, platform lenticular in outline, fused carina looks like a high wall and reaching beyond the posterior margin., (3) Those forms with high and highly fused posterior carina, which does not reach beyond the posterior margin. The base of the Changhsingian has been suggested as the first appearance datum (FAD) of Clarkina wangi which characterized by drop-like, with a short and wide platform, usually no free blade; fused carina looks like a high wall and reaching beyond the posterior margin.