The early Silurian Chongqing Lagerstätte(middle Telychian)yields exceptionally preserved articulated jawless and jawed fishes.Here,we describe a new eugaleaspiform(Galeaspida,jawless stem-Gnathostomata),Miaojiaas...The early Silurian Chongqing Lagerstätte(middle Telychian)yields exceptionally preserved articulated jawless and jawed fishes.Here,we describe a new eugaleaspiform(Galeaspida,jawless stem-Gnathostomata),Miaojiaaspis dichotomus gen.et sp.nov.,from the Chongqing Lagerstätte in Xiushan,Chongqing,China.The new form resembles Tujiaaspis vividus in the short medial dorsal canal,and the presence of the branching ends of the lateral transverse canal.They differ in that T.vividus has highly developed subordinate branches of the sensory canals that form a reticulate sensory canal system,and the median dorsal opening is more elongated.Our phylogenetic analysis recovers M.dichotomus and T.vividus as a monophyletic clade(Tujiaaspidae fam.nov.),which is supported by two synapomorphies:the short medial dorsal canal,and the branching ends of the lateral transverse canal.Tujiaaspidae forms a trichotomy with Shuyuidae and a clade comprising Anjiaspis,Sinogaleaspidae,Yongdongaspidae,and the‘eugaleaspid cluster’.The sensory canal patterns in galeaspids are compared to show the transformation sequence of the sensory canal system in Eugaleaspiformes.展开更多
文摘The early Silurian Chongqing Lagerstätte(middle Telychian)yields exceptionally preserved articulated jawless and jawed fishes.Here,we describe a new eugaleaspiform(Galeaspida,jawless stem-Gnathostomata),Miaojiaaspis dichotomus gen.et sp.nov.,from the Chongqing Lagerstätte in Xiushan,Chongqing,China.The new form resembles Tujiaaspis vividus in the short medial dorsal canal,and the presence of the branching ends of the lateral transverse canal.They differ in that T.vividus has highly developed subordinate branches of the sensory canals that form a reticulate sensory canal system,and the median dorsal opening is more elongated.Our phylogenetic analysis recovers M.dichotomus and T.vividus as a monophyletic clade(Tujiaaspidae fam.nov.),which is supported by two synapomorphies:the short medial dorsal canal,and the branching ends of the lateral transverse canal.Tujiaaspidae forms a trichotomy with Shuyuidae and a clade comprising Anjiaspis,Sinogaleaspidae,Yongdongaspidae,and the‘eugaleaspid cluster’.The sensory canal patterns in galeaspids are compared to show the transformation sequence of the sensory canal system in Eugaleaspiformes.
