New findings of Xiyuichthys  (Xiushuiaspidae, Galeaspida) from the Silurian of Jiangxi Province and Tarim Basin

doi:10.19615/j.cnki.2096-9899.230904

Abstract

Abstract:

New findings of the early Silurian Xiyuichthys (Xiushuiaspidae, Galeaspida), Xiyuichthys lixiensis sp. nov. and X. zhangi are described from the Qingshui Formation in Jiangxi Province and the Tataertag Formation in Tarim Basin respectively. X. lixiensis sp. nov. is characterized by the partially serrated lateral margin of the headshield and the ornamentation composed of extremely coarse granular tubercles (one tubercle per square millimetre). The complete early Silurian biostratigraphic sequence in northwestern Jiangxi warrants the erection of a standard section for the correlation of Silurian shallow marine red beds in South China and Tarim blocks. Thus, the finding of X. lixiensis from the Qingshui Formation (Silurian Lower Red Beds) in Jiujiang of Jiangxi bears important biostratigraphic significance. It can directly compare to X. zhangi from the Tataertag Formation in Tarim Basin on the specific level, which corroborates the correlations between the Tataertag Formation in Tarim Block and the Silurian Lower Red Beds in South China. Fossil records suggest that Xiushuiaspidae have a relatively broader stratigraphic range, but exhibit distinct composition at different stratigraphic horizons, with Xiyuichthys and Changxingaspis arising in the Silurian Lower Red Beds (Qingshui, Tangchiawu, and Tataertag formations) and Xiushuiaspis occurring in the Silurian Upper Red Beds (Xikeng Formation).

Key words: northwestern Jiangxi, Tarim Basin, early Silurian, Qingshui Formation, Tataertag Formation, Galeaspids, biostratigraphy

摘要：

描述了盔甲鱼亚纲修水鱼科西域鱼属在中国志留系的新发现，包括江西九江清水组的一新种——澧溪西域鱼(Xiyuichthys lixiensis sp. nov.)和新疆塔里木盆地塔塔埃尔塔格组的张氏西域鱼(X. zhangi )新材料。澧溪西域鱼的典型特征为：部分头甲侧缘呈锯齿状；头甲纹饰由极为粗大的瘤状突起组成(每平方毫米仅有1个突起)。赣西北志留纪早期生物地层序列较为完整，可以建立标准剖面，为华南和塔里木板块志留纪浅海红层的对比提供参照。因此，澧溪西域鱼在赣西北志留系下红层清水组中的发现具有重要的生物地层意义。该种能和塔里木盆地塔塔埃尔塔格组中的张氏西域鱼直接对比，进一步支持塔里木板块的塔塔埃尔塔格组和华南板块的志留系下红层之间的对应关系。化石记录显示，修水鱼科具有较长的地层延限，但在不同的层位显示出不同的组成面貌，其中西域鱼属和长兴鱼属出现在志留系下红层(清水组、唐家坞组和塔塔埃尔塔格组), 修水鱼属则出现在志留系上红层(西坑组)。

关键词: 赣西北，塔里木盆地, 志留纪早期, 清水组，塔塔埃尔塔格组, 盔甲鱼类, 生物地层

CLC Number:

Q915.861

SHAN Xian-Ren, LIN Xiang-Hong, ZHANG Yu-Meng, LI Xu-Tong, GAI Zhi-Kun. New findings of Xiyuichthys (Xiushuiaspidae, Galeaspida) from the Silurian of Jiangxi Province and Tarim Basin. Vertebrata Palasiatica, 2023, 61(4): 245-260.

山显任, 林翔鸿, 张雨萌, 李旭彤, 盖志琨. 2023, 61(4): 245-260, 西域鱼在江西和塔里木盆地志留系的新发现. 古脊椎动物学报.

Figures/Tables 9

Fig. 1 Lithological columns of the Silurian fish-bearing strata in Wuning and Kalpin A. Wuning, Jiangxi (based on Liu, 1997); B. Kalpin, Xinjiang (modified from Zhao et al., 2009)

Fig. 2 Photographs of Xiyuichthys lixiensis sp. nov. in ventral view A, B. internal (A) and external (B) moulds of an incomplete headshield, IVPP V26119.1a, b, holotype; C, D. internal (C) and external (D) moulds of an incomplete headshield, V26119.2a, b, paratype; E. close-up of the pineal opening, box region 1 of Fig. 2B; F. close-up of box region 2 of Fig. 2B, showing the ornamentation of the headshield. Abbreviations: ifc. infraorbital canal; ldc. lateral dorsal canal; ltc. lateral transverse canal; md.o. median dorsal opening; mtc. median transverse canal; orb. orbital opening; pi. pineal opening

Fig. 3 Photographs of Xiyuichthys lixiensis sp. nov. in ventral view A. an external mould of an incomplete headshield, IVPP V26119.3; B. an incomplete ventral rim of the headshield, V26119.4 Abbreviations: br.o. branchial opening; ic. inner cornual process; vr. ventral rim

Fig. 4 Restoration of Xiyuichthys lixiensis sp. nov. in dorsal (A) and ventral (B) views For abbreviations see Figs. 2, 3

Table 1 Measurements and comparisons of Xiyuichthys lixiensis sp. nov. and X. zhangi (mm)

Items	X. lixiensis		X. zhangi
Items	IVPP V26119.1	V26119.2	GMC V24162.1(Liu et al., 2019)	IVPP V25445.4
Maximum length of headshield	>72.8	>63.2	110.0	103.2
Maximum width of headshield	123.4	>97.3	115.0	105.3
Diameter of orbital opening	5.7	5.8	7.1	-
Distance between orbital openings	24.8	24.6	-	-
Long axis of median dorsal opening	23.3	23.4	-	-
Short axis of median dorsal opening	5.6	8.6	-	-
Diameter of the pineal opening	1.2	1.3	-	-
Length of the pre-pineal region	18.2	19.5	-	-

Fig. 5 Photographs and interpretive drawing of Xiyuichthys zhangi A. internal mould of an incomplete headshield, IVPP V25445.4a, in dorsal view; B. an external mould of an incomplete headshield, V25445.4b, in ventral view; C. an incomplete ventral rim of the headshield (after removing the dorsal headshield of V25445.4a), in ventral view; D. interpretive drawing of Fig. 5C For abbreviations see Figs. 2 and 3 plus obr.c. oralobranchial chamber

Fig. 6 Restoration of Xiyuichthys zhangi in dorsal (A) and ventral (B) views For abbreviations see Figs. 2, 3

Fig. 7 Biostratigraphic sequence of Telychian (Llandovery, Silurian) brachiopods, trilobites, bivalves, gastropods, and fishes in northwestern Jiangxi Data from Pan and Wang, 1980; Zhang, 1982; Shan et al., 2020, 2022b, 2023a. Abbreviation: Fm. Formation

Fig. 8 Stratigraphical positions and correlations of the Silurian marine red beds in South China and Tarim Basin Modified from Rong et al., 2019; Shan et al., 2023b Abbreviations: Fm. Formation; Mb. Member; MRBs. marine red beds

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