摘要: A new genus and species of the family Eugaleaspidae (Eugaleaspiformes, Galeaspida),
Xitunaspis magnus gen. et sp. nov., is described from the Lower Devonian Xitun Formation
in Qujing, Yunnan Province, China. The new genus displays the diagnostic characters of the
Eugaleaspidae, including a slit-like median dorsal opening, no inner cornual process, developed
median dorsal canals, and only three pairs of lateral transverse canals extending from lateral dorsal
canals. Different from the other eugaleaspids, X. magnus possesses a large headshield with thick
dermal bone and a more plesiomorphic sensory canal system. The phylogenetic analysis of the
Galeaspida reveals that Xitunaspis clusters with Dunyu and Eugaleaspis to form a monophyletic
clade Eugaleaspidae Liu, 1965, and has a closer relationship with Dunyu than Eugaleaspis by
sharing the thick dermal bone of the headshield. The new finding represents the first convincing
fossil record of the Eugaleaspiformes in the middle Lochkovian Xitun Formation and adds to our
knowledge about the morphology of eugaleaspiforms and the evolutionary pattern of the sensory
canal system in the Eugaleaspiformes and even Galeaspida.