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| Miaojiaaspis dichotomus Chen, Li, Zhou, Shan, Y.-A. Zhu, Wang, Wei & M. Zhu, 2024 |
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.
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| Photographs (A, C) and interpretative drawings (B, D) of Miaojiaaspis dichotomus gen. et sp. nov. from Xiushan, Chongqing A, B. an incomplete internal mold of the headshield with the trunk articulated, CIGMR V0125a; C, D. an incomplete external mold of the headshield with the trunk articulated, holotype, CIGMR V0125b |
Subclass Galeaspida Tarlo, 1967
Order Eugaleaspiformes (Liu, 1965) Liu, 1980
Family Tujiaaspidae fam. nov.
Type genus Tujiaaspis Gai et al., 2022.
Referred genus Miaojiaaspis gen. nov.
Differential diagnosis Tujiaaspidae differs from other families of Eugaleaspiformes in the short medial dorsal canal, and the branching ends of the lateral transverse canal.
Remarks Our phylogenetic analysis shows that M. dichotomus and T. vividus form a monophyletic clade supported by two synapomorphies.
Genus Miaojiaaspis gen. nov.
Type species Miaojiaaspis dichotomus sp. nov.
Etymology From Miaojia, Pinyin for the Miao People, a minority ethnic group in China, which is one of the two main autonomous minority ethnic groups in Xiushan County, Chongqing, and aspis (Gr.), shield.
Differential diagnosis M. dichotomus differs from T. vividus in a more subtriangular headshield, no highly developed subordinate branches of sensory canals and a shorter median dorsal opening.
Miaojiaaspis dichotomus sp. nov.
Holotype An incomplete headshield with the trunk articulated, CIGMR V0125a, b (Figs. 2–3).
Referred specimens 8 complete headshields, CIGMR V0126–V0129, IVPP V28714–V28717 (Fig. 4).
Etymology From dichotomus (Latin), referring to the dichotomous ends of the lateral transverse canals.
Diagnosis Small-sized eugaleaspiform fish with a subtriangular headshield. Spine-shaped cornual and inner cornual processes caudo-laterally or caudally oriented. Longitudinal oval-like median dorsal opening. Pineal opening positioned behind the posterior margin of the orbits. Funnel-shaped supraorbital canals. Short medial dorsal canal.
CHEN Yang, LI Qiang, ZHOU Zheng-Da, SHAN Xian-Ren, ZHU You-An, WANG Qian, WEI Guang-Biao, ZHU Min. 2024. A New Genus of galeaspids (jawless stem-Gnathostomata) from the early Silurian Chongqing Lagerstätte, China. Vertebrata Palasiatica. 62(4); 245-261. DOI: 10.19615/j.cnki.2096-9899.240820
