记比耶鱼(Birgeria)在中国的首次发现

NOTES ON THE DISCOVERY OF BIRGERIA IN CHINA

记述了采自云南罗平晚三叠世法郎组竹杆坡段的比耶鱼一新种──刘氏比耶鱼（Ｂｉｒｇｅｒｉａ ｌｉｕｉ ｓｐ． ｎｏｖ．），这是比耶鱼化石在中国的首次发现。刘氏比耶鱼与产自瑞士圣乔治山中三叠世边境沥青层的史氏比耶鱼最为相近，两者仅在尾柄长高之比、尾鳍长短与上下叶外缘交角、背鳍和臀鳍辐状支鳍骨的数目、臀鳍辐状骨骨板的大小、以及侧线管骨化与否等特征上略有差异。比耶鱼与软骨硬鳞鱼超目的鲟形目最为接近，两者共有一系列特征，如除尾上叶外体侧裸露，副蝶骨末端伸达头后，鳃盖骨退化；但比耶鱼同时也具有不少的特有特征，代表了软骨硬鳞鱼超目的另一类群──比耶鱼目（Ｂｉｒｇｅｒｉｉｆｏｒｍｅｓ ｏｒｄ． ｎｏｖ．）。刘氏比耶鱼的发现进一步表明华南扬子区中、晚三叠世鱼类化石与特提斯西部的鱼群具有密切的动物地理关系。

An incomplete specimen of algeria is described in the present ~r, which is from the early be Triassic Zhuganpo Member of the Falang Formation in Luoping of Yunnan Province, South China. Although thes new specimen is lack of skull and anterior Pat of the body, itS preserved chacters are in well agreement with the diagnoses of Birgeria: A large fusiform fish about 800 nun in total length; peduncle slender; body naked without scales and bony Plaaes except on the upper lobe of the caudal fin; veheblal elements ossified. Paired basidorsals and basiventrals in the caudal regioll, except the anteriormost 10 pairs of basidorsals, fuSed with each other distally as single netal spines and bernal spines; dorsal and anal fins sitUated backward. anal fin slightly f^r back than the dorsal fin, both with more than 50 fin rays; pterygiophores of the dorsal and anal fins with tWo series of ossifications: proximal and ndddie radials; proximal pterygiophore series of the anal fin including anterior long radials and POsterior normal radials, at the end of thes series with a small Plate evidently ccrossified from the posteriormost proximal edals; caudal fin deeply cleft and nearly equllobate, with well developed dorsal caudal fulcra and more than 60 fin rays; scales on the uPPer caudal lobe long and narrow, without peg--and- socket articulation. Among the known species of Birgeria, the specimen discovered for the first bine in China is steadily dishnchve from the Early Triassic forms (B. groenlandica, B.nielseni, B. aldl'ngerl) in itS slender caudal Peduncle and longer caudal region (the pedUncle length is 2.7 bines of itS depth, and there are 36 metameres in the caudal region besides those in the caudal fin), relahvely forward dorsal and anal fins (the commencement of the dorsal and anal fins is opposite to the 29th and 22nd precaudal metameres respechvely), and more stronger caudal fin (the dorsal and ventral margins of the caudal fin intersect in 70'); whereas the new specimen is quite similar to the Middle Triassic B. stensiol from GrenzbitUmen--horizon of Monte San caorgio in southern SwitZerland. At present the Chinese specimen is only discriminated from B. stensi6'i by donor differences in the caudal region: ratio of the caudal peduncle length tO the depth. length of the caudri fin and itS intersechng angle of the dorsal and vental ~ins, number of the pterygiophores of the dorsal and anal fins, size of the proximal edal plaal of the anal fin, and larend line canal ossifications. It is jushfied tO assume that there must be some differences in the skull betWeen the Chinese specimen and the Switseriand species of BirgeriQ because the known species of thes genus are banly dishngulshed by the characters from head skeletons. Hence, the Chinese specimen is assigned to a new species -- B. Iiui sp. nov. The species name is in honor of the Chinese paleoichthyologist LIU Xian--Ting (LIU H8ien--Ting), who Passed away at the begining of this new ndlleedum. The systematic POsihon of the monogeneric mdly Birgeridae is yet to be revised using the Phylogenehc Principles. Tndhonally, Birgeridae was refered tO Palaeonisciformes or to Chondrostei as a side--branch of the POlyedonhd fishes. Among the lower achnopterygian fishes, Birgerithe is most closely related to Acipenseriformes, especially to the fossil acipenseriform fndlies Chondrosteifor and Peipiaosteidae. At least Birgeridae and Acipenseriformes share the following oh^ters:body naked without scales and bony Plates except on the upper caudal lobe, broad parasphenoid extending baCkward beyond the posterior end of endocndum, operele reduced, caudal fin deeply cleft and nearly equllobate. On the other hand, birgerid fishes possess quite a few peculiar fe^s, e. g. a series of 8-- 11 long and narrow suborbitals, suboperele consishng of 4~ 6 triangular Plates, netal spines singulax in the caudal region, and they are most probably representatives of another clade aped from Acipenseriformes in the present superorder Chondrostei, which is newly named as Biygeriiformes. BI'rgeria lint sp. nov., and the pre