Abstract: The Ionoscopiformes are a fossil lineage of halecomorphs known only from the Mesozoic marine deposits. Because of their close relationships with the Amiiformes, the Ionoscopiformes are phylogenetically important in investigating the early evolution and biogeography of the Halecomorphi. However, fossil evidence of early ionoscopiforms was scarce; until recently,Robustichthys from the Middle Triassic Luoping Biota, eastern Yunnan,China, represents the oldest and only known ionoscopiform in the Triassic. Here we report the discovery of a new ionoscopiform, Panxianichthys imparilis gen. et sp. nov., on the basis of two well preserved specimens from the Middle Triassic Panxian Biota, western Guizhou, China. The discovery documents the second ionoscopiform in the Middle Triassic; although Panxianichthys is slightly younger than Robustichthys, it is significantly older than other members of this group from the Late Jurassic of Europe, and Early Cretaceous of North and South America. Panxianichthys possesses an important synapomorphy of the Ionoscopiformes: a sensory canal in the maxilla, but retains some primitive characters unknown in other ionoscopiforms. Results of our phylogenetic analysis recover Panxianichthys as the most primitive ionoscopiform, and provide new insight on the early evolution of this clade. The interrelationships of the Ionoscopidae have been reassessed;Quetzalichthysis regarded more closely related to Ionoscopus than to Oshunia. In addition, our analysis supports the reassessment of Furo muensteri as an ophiopsid ionoscopiform. The successive discoveries of Robustichthys andPanxianichthys from China indicate that the early diversification of the Ionoscopiformes is more rapid than previously thought.

摘要： 预言鱼目是中生代海生近鲱形类的一个绝灭的支系。由于与弓鳍鱼目密切的亲缘关系，预言鱼目在研究近鲱形类的早期演化和生物地理学中具有重要意义。然而，早期预言鱼目的化石证据非常匮乏；直到最近，产于云南中三叠世罗平生物群的强壮鱼是该目中最古老的也是三叠纪唯一的成员。本文根据产于贵州西部中三叠世盘县动物群的两块保存良好的标本命名了预言鱼目一个新的属种，奇异盘县鱼(Panxianichthys imparilis gen. et sp. nov.)。盘县鱼的生存时代略晚于强壮鱼，但它比产于欧洲晚侏罗世和美洲早白垩世的预言鱼目其他成员要早很多。盘县鱼具有预言鱼目的共近裔性状，上颌骨上具有感觉管，但它保留了一些其他预言鱼目鱼类所不具有的原始特征。分支分析的研究结果表明盘县鱼是最原始的预言鱼目鱼类，为揭示预言鱼目的演化提供了新的信息。强壮鱼和盘县鱼的相继发现表明，预言鱼目的早期分异比我们之前想象的要快得多。