NOTES ON THE DISCOVERY OF BIRGERIA IN CHINA
2001; Linguagem: Inglês
ISSN
1000-3118
Autores Tópico(s)Ichthyology and Marine Biology
ResumoAn 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
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