A new genus of galeaspids (jawless stem-Gnathostomata) from the early Silurian Chongqing Lagerstätte, China

doi:10.19615/j.cnki.2096-9899.240820

Abstract

Abstract:

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.

Key words: Chongqing Lagerstätte, Telychian, Galeaspida, morphology, phylogeny

摘要：

志留纪(特列奇期)重庆特异埋藏化石库产出了大量完整保存的无颌类和有颌鱼类化石。描述了采自重庆秀山的真盔甲鱼目一新属种——双叉苗家鱼(Miaojiaaspis dichotomus gen. et sp. nov. )。新属种具有与灵动土家鱼(Tujiaaspis vividus)相似的特征，包括短的中背管和分叉的侧横管。二者的区别是：灵动土家鱼的侧线系统极度发育，形成了网状的感觉管，且具有更长的中背孔。系统发育分析结果显示，苗家鱼与土家鱼共同组成一个单系类群——土家鱼科(新科)。该新科具有两个共有衍征：短的中背管，以及侧横管末端分叉。隶属真盔甲鱼目的土家鱼科、曙鱼科以及一个包含了安吉鱼属、中华盔甲鱼科、涌洞鱼科和 “真盔甲鱼簇” 的支系构成了一个三分支。对盔甲鱼类的侧线系统进行了比较，并讨论了真盔甲鱼目侧线系统的特征演化序列。

关键词: 重庆特异埋藏化石库, 特列奇期, 盔甲鱼亚纲, 形态学, 系统学

CLC Number:

Q915.861

CHEN Yang, LI Qiang, ZHOU Zheng-Da, SHAN Xian-Ren, ZHU You-An, WANG Qian, WEI Guang-Biao, ZHU Min. A new genus of galeaspids (jawless stem-Gnathostomata) from the early Silurian Chongqing Lagerstätte, China. Vertebrata Palasiatica, 2024, 62(4): 245-261.

陈阳, 李强, 周政达, 山显任, 朱幼安, 王倩, 魏光飚, 朱敏. 2024, 62(4): 245-261, 重庆特异埋藏化石库盔甲鱼类一新属. 古脊椎动物学报.

Figures/Tables 7

Fig. 1 Locality and geological setting of Miaojiaaspis dichotomus gen. et sp. nov. A. remote sensing images of the fossil site; B. regional geological map at the fossil locality in Lianghe Village, Yongdong Township, Xiushan County, Chongqing Municipality, southwestern China; C. stratigraphic column of the fossil site

Fig. 2 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

Fig. 3 Close-up photographs of Miaojiaaspis dichotomus gen. et sp. nov. from Xiushan, Chongqing A. continuation from the lateral dorsal canal to the trunk canal (box a in Fig. 2); B. ventrolateral fin on the trunk (box b in Fig. 2); C. scales along the median dorsal ridge (box c in Fig. 2); D. trunk canal embedded in the scales (box d in Fig. 2)

Fig. 4 Photograph (A), interpretative drawing (B), and restoration (C) of the headshield of Miaojiaaspis dichotomus gen. et sp. nov. from Xiushan, Chongqing in dorsal view A, B. CIGMR V0127; C. restoration

Table 1 Measurements of headshields of Miaojiaaspis dichotomus gen. et sp. nov. in dorstal aspect (mm)

Item	CIGMR V					IVPP V				Average
Item	0125	0126	0127	0128	0129	28714	28715	28716	28717	Average
Maximum length of the head-shield	17.1	20.5	—	—	—	18.3	19.4	18.2	—	18.7
Maximum width of the head-shield	—	21.1	—	17.8	—	18.6	—	—	—	19.2
Length of the head-shield in midline	13.8	12.6	12.7	—	15.1	13.9	13.1	13.4	—	13.5
Diameter of the orbit	1.8	1.9	1.5	—	1.9	1.8	1.6	—	1.6	1.7
Distance between the orbit	—	8.2	7.4	8.1	7.9	8.2	7.5	—	7.8	7.9
Long axis of the median dorsal opening	3.4	3.5	3.2	2.8	3.6	3.2	3.8	3.3	3	3.3
Short axis of the median dorsal opening	1.3	1.1	1.5	1.4	1.6	1.5	1.6	1.5	1.4	1.4
Length of the pre-pineal region in midline	6.6	6.4	6.44	5.5	6.9	6.6	6.4	5.8	5.9	6.3
Length of the post-pineal region in midline	7.2	6.2	6.26	—	8.2	7.3	6.7	7.6	—	7.1

Fig. 5 Strict consensus tree of the three most parsimonious trees of the galeaspids

Fig. 6 The sensory canal system in basal galeaspids and eugaleaspiforms Numbers (1-4) are used to denote the nodes discussed in the text Dayongaspis colubra redrawn from Zhang et al., 2023; Hanyangaspis guodingshanensis redrawn from Gai and Zhu., 2017; Shuyu zhejiangensis redrawn from Gai et al., 2011; Tujiaaspis vividus redrawn from Gai et al., 2022; Sinogaleaspis shankouensis redrawn from Gai et al., 2020; Yongdongaspis littoralis redrawn from Chen et al., 2022; Yunnanogaleaspis major redrawn from Pan and Wang, 1980; Eugaleaspis changi redrawn from Liu, 1965

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