湘西早志留世溶溪组无颌类的发现及其意义

本文记述了在湖南西部早志留世 Llandovery 期溶溪组发现的多鳃鱼目—新科——大庸鱼科 (Dayongaspidae fam. nov), 其标本代表了中国迄今为止地质时代最早的海生早期脊椎动物化石,并进而论证了中国的盔甲鱼类发生在近岸浅海地区,而不是大陆淡水盆地,其时代为前早志留世.扬子区是这类无颌类的发源地.

DAYONGASPIDAE, A NEW FAMILY OF POLYBRANCHIASPIFORMES (AGNATHA) FROM EARLY SILURIAN OF HUNAN, CHINA

The Llandovery jawless Vertebrate described in this paper was collected by the authors during the 1982-1983 field seasons from the uppermost Part of Rongxi Formation in Wentang, Dayong district, western part of Hunan Province (see fig. l and fig. 2). It is the jawless vertebrate discovered in China and oldest in Asia as well. The early vertebrates in China are chiefly distributed in the Lower Yangtze River (Ckang Jiang) region. Their earliest record is from the Upper Llandovery marine formations of Souch China. The Eugaleaspida are known only from China and are regarded as endemie early vertebrates. The Hangyangaspids and Polybranchiaspids were epicongnental forIns of Early and Middle Silurian of China. All the specimens described are in the collections of the Museum of Geology, Beijng. Polybranchiaspiformes Liu 1965 Dayongaspidae (fam. nov.) Dayongaspis. (gen. nov.) Dayongaspis hunanensis (gen. et sp. nov.) (pls. 1-2, figs. 3-4) Polybranehianspiforths of medium size, cephalic shield nearly triangular in outline, length from rostrum to tip of inner cornua abcut 6-7 cm, maximum width about 10 cm, the length shorter than the breadth, lateral margines serrated. Naso-hypvphysial opening circular in stmpe and near to the rostral margin. Orbital opening near to the mid-line of cephalic shield and naso-hypophysial opening. Pectoral cornua and inner latoral cornua well developed, but of the two the latter much bigger than the former. A pair of longitudinal main lateral canals, wich eight shorter transerversal branches, and two median dorsal conmmissura canals.