Xitunaspis, a new eugaleaspid fish (Eugaleaspiformes, Galeaspida) from the Lower Devonian of Qujing, Yunnan

doi:10.19615/j.cnki.2096-9899.220412

Abstract

Abstract:

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.

Key words: Qujing, Yunnan, Early Devonian, Xitunaspis, Eugaleaspiformes, sensory canal system

摘要：

记述了采自云南曲靖下泥盆统西屯组中的真盔甲鱼科一新属种——硕大西屯鱼(Xitunaspis magnus gen. et sp. nov.)。新属具有真盔甲鱼科的典型特征,包括一个纵长裂隙状的中背孔、没有内角、发达的中背管以及只有3对从侧背管上伸出的侧横管等,但其具有大而厚的头甲以及更原始的感觉管系统等特征明显区别于其他真盔甲鱼类。系统发育分析表明,西屯鱼属(Xitunaspis)与盾鱼属 (Dunyu)和真盔甲鱼属(Eugaleaspis)共同组成一个单系类群——真盔甲鱼科支系(Eugaleaspidae Liu, 1965), 并且三者之间西屯鱼与盾鱼的亲缘关系更为密切。作为曲靖地区下泥盆统西屯组中确凿的真盔甲鱼类化石记录,西屯鱼的发现加深了对真盔甲鱼类形态学及真盔甲鱼目乃至盔甲鱼亚纲中感觉管系统演化的认知。

关键词: 云南曲靖, 早泥盆世, 真盔甲鱼类,西屯鱼, 感觉管系统

CLC Number:

Q915.861

SUN Hao-Ran, GAI Zhi-Kun, CAI Jia-Chen, LI Qiang, ZHU Min, ZHAO Wen-Jin. Xitunaspis, a new eugaleaspid fish (Eugaleaspiformes, Galeaspida) from the Lower Devonian of Qujing, Yunnan. Vertebrata Palasiatica, 2022, 60(3): 169-183.

孙浩然, 盖志琨, 蔡家琛, 李强, 朱敏, 赵文金. 2022, 60(3): 169-183, 滇东曲靖地区早泥盆世真盔甲鱼科一新属种. 古脊椎动物学报.

Figures/Tables 7

Fig. 1 Map showing the fossil locality (A) and the fish-bearing lithological column (B) in Qujing Revised from Si et al., 2015; Meng et al., 2021

Fig. 2 Photographs of Xitunaspis magnus gen. et sp. nov. from the Xitun Formation in Qujing A, B. the external (A) and internal mould (B) of a nearly complete headshield, IVPP V 27400.1 (holotype); C, D. two incomplete headshields, V 27400.2 (C), V 27400.3 (D); E. close-up of the median dorsal opening of V 27400.3. A. in ventral view; B-E. in dorsal view; scale bars equal 10 mm Abbreviations: c. cornual process; ifc. infraorbital canal; md.o. median dorsal opening; orb. orbital opening; pi. pineal opening; ri. dermal ring encircling median dorsal opening; spi. spine-like ridge on the dermal ring of median dorsal opening

Fig. 3 Photographs of Xitunaspis magnus gen. et sp. nov. and its CT slices A. photograph of a nearly complete headshield V 27400.4; B. CT slice of V 27400.4, showing the sensory canal system; C. close-up of the pineal opening (box inset 1 of Fig. 3A); D. close-up of tubercles (box inset 2 of Fig. 3A); E. close-up of vascular plexus (box inset 3 of Fig. 3A); F. close-up of vascular plexus (box inset 4 of Fig. 3A); G. CT slice of V 27400.4, showing the middle region of the headshield A, C-F. in ventral view; B, G. in dorsal view; scale bars in A, B and G equal 10 mm, scale bars in C-F equal 1 mm For abbreviations see Fig. 2 plus cc. central canal; dcm. dorsal commissure; ldc. lateral dorsal canal; ltc. lateral transverse canal; mdc. median dorsal canal; soc1. anterior supraorbital canal; soc2. posterior supraorbital canal; v. mtc. vestige of median transverse canal

Table 1 Measurements of Xitunaspis magnus gen. et sp. nov. from Qujing (mm)

Items	IVPP V 27400
Items	1a	1b	2	3	4
Maximum length of the headshield	—	103.4	—	—	—
Maximum width of the headshield	146.0	146.0	—	—	—
Length of the headshield in midline	—	85.0	—	—	—
Diameter of the orbital openings	10.0	10.0	9.0	10.1	10.1
Distance between the orbital openings	44.0	44.0	—	—	39.0
Long axis of the median dorsal opening	34.2	34.2	—	—	34.0
Short axis of the median dorsal opening	4.2	4.2	—	—	3.5
Length of the pre-pineal region in midline	50.0	—	—	—	—
Length of the post-pineal region in midline	34.1	—	—	—	—

Fig. 5 Strict consensus tree of the two most parsimonious trees and cladistically-based classification of the basal galeaspids and Eugaleaspiformes The clade Polybranchiaspidida is simplified and same as that in Shan et al., 2020. Tree length = 198, consistency index (CI) = 0.4192, retention index (RI) = 0.7609, numbers on branches denote bootstrap frequencies (above node) and Bremer support values (below node), bootstrap frequencies below 50 are not shown

Fig. 6 The sensory canal system of galeaspids in different groups (revised from Shan et al., 2020) A, B. plesiomorphic taxa: A. Hanyangaspis guodingshanensis (P’an et al., 1975; Pan, 1986); B. Changxingaspis gui (Wang, 1991); C-J. Eugaleaspiformes: C. Meishanaspis lehmani (Gai et al., 2005); D. Rumporostralis xikengensis (Shan et al., 2020); E. Nochelaspis maeandrine (Zhu, 1992); F. Dunyu longiforus (Zhu et al., 2012); G. Xitunaspis magnus; H. Eugaleaspis changi (Liu, 1965); I. E. xujiachongensis (Liu, 1975); J. Pterogonaspis yuhaii (Zhu, 1992); K. Polybranchiaspiformes: Polybranchiaspis liaojiaoshanensis (Liu, 1975); L. Huananaspiformes: Sanchaspis magalarostrata (Pan and Wang, 1981). Scale bars equal 10 mm Abbreviations: 1-6. the first to sixth lateral transverse canal or median transverse canal issuing from lateral dorsal canal; a-c. the first to third lateral transverse canal issuing from the infraorbital canal; ic. inner cornual process; mtc. median transverse canal; nc.p. pore for passage of the neural canal; pb.w. postbranchial wall; poc. preorbital commissure; ro. rostral process; v.mdc. vestige of median dorsal canal; other abbreviations see Figs. 2-3

Fig. 4 Reconstruction of Xitunaspis magnus gen. et sp. nov. in dorsal view A. 3D reconstruction of IVPP V 27400.4 based on Micro-CT scanning; B. restoration of the headshield by Feng Mingjuan; C. life restoration by Shi Aijuan; scale bars equal 10 mm For abbreviations see Figs. 2-3

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