河北围场地区发现早白垩世七鳃鳗化石

Discovery of Early Cretaceous fossil lampreys from Weichang area,Hebei Province,China

七鳃鳗是一种古老而原始的特殊无颌类脊椎动物。因其仅发育脊索上的小软骨片及口腔内的角质齿,一般很难保存为化石。国内外现存的七鳃鳗化石记录很少,例如南非晚泥盆世的Priscomyzon riniensis、北美石炭纪的Mayomyzon pieckoensis和Hardistiella montanensis,还有我国内蒙古下白垩统义县组的Mesomyzon mengae。近几年,在河北承德围场地区早白垩世地层中发现了丰富的鱼类化石,其中就有七鳃鳗化石,表明围场地区是继内蒙古宁城之后我国第二个重要的早白垩世七鳃鳗化石产地。研究了产自围场地区早白垩世九佛堂组的3件七鳃鳗化石标本(MHGU4270、MHGU4271、MHGU4272),化石保存基本完整,可见吸盘、眼、鳃囊、肌节、背鳍、后背鳍、尾鳍等构造。成年期个体(MHGU4270、MHGU4271)体长为24~27 cm,体高为1.9~2.0 cm;非成年期个体(MHGU4272)体长约为17.0 cm,体高约为1.2 cm,明显大于内蒙古宁城地区发现的孟氏中生鳗。根据形态结构特征,认为这3件七鳃鳗化石应为一个新的属种,将其命名为围场河北鳗(Hebeimyzon weichangensis gen.et sp.nov.)。围场中生鳗(新属、新种)的发现不仅为我国早白垩世七鳃鳗化石的研究增添了新材料,扩大了研究的区域范围,而且对进一步深化研究早白垩世七鳃鳗的演化历史、生活习性、生态环境和古地理分布具有重要科学价值。

Lampreys are a kind of ancient and primitive jawless vertebrates.With only small cartilaginous lamellae in the notochord and horny teeth in the oral cavity,lampreys are difficult to be preserved as fossils.There has been a few records of fossil lampreys in the world,such as Late Devonian Priscomyzon riniensis from South Africa,Carboniferous Mayomyzon pieckoensis and Hardistiella montanensis from North America,and Early Cretaceous Mesomyzon mengae from the Yixian Formation of Inner Mongolia,North China.In recent years,rich Early Cretaceous fossil fishes have been unearthed,including fossil lampreys,from Weichang County of Chengde in Hebei,China.This indicates that the Weichang area is the second important fossil site of Early Cretaceous lampreys in China after the fossil site of the Ningcheng area,Inner Mongolia.This paper mainly deals with 3 specimens of Early Cretaceous lampreys(MHGU4270,MHGU4271 and MHGU4272)unearthed from the Jiufotang Formation in the Weichang area.The fossil lampreys are well preserved with sucker,eyes,gill pouch,myotome,dorsal fin,second dorsal fin and caudal fin.The adult individuals(MHGU4270 and MHGU4271)are about 24-27 cm in length and about 1.9-2.0 cm in height.The non-adult individual(MHGU4272)is about 17.0 cm in length and 1.2 cm in height.It is clear that the individuals are much larger than those of Mesomyzon mengae from the Ningcheng area of Inner Mongolia.Based on the study of the morphological and structural features,this paper believes that the 3 fossil lampreys should fall into a new Early Cretaceous lamprey:Hebeimyzon weichangensis gen.et sp.nov.This discovery not only adds new materials for the study of Early Cretaceous lampreys in China,expands its regional scope,but also has great scientific value for the further study of the evolutionary history,living habits,ecological environment and paleogeographic distribution of early Cretaceous lampreys.