Redescription of Nochelaspis maeandrine ,the largest eugaleaspiform from the Lower Devonian of Qujing, Yunnan

doi:10.19615/j.cnki.2096-9899.210727

Abstract

Abstract:

The new specimens of the largest eugaleaspiform Nochelaspis maeandrine are redescribed from two localities of the Xishancun Formation in Qujing City, Yunnan Province, southwestern China. Nochelaspis is most suggestive of Yunnanogaleaspis from the same horizon, but differs in its slit-like median dorsal opening (length/width>6), much stronger inner cornual process, coarse stellate ornamentation, and the serrations along the edges of the median dorsal opening and headshield. The new findings reveal the morphological details on the ventral side of the headshield as well. The oralobranchial fenestra is covered by a large dermal ventral plate, which is decorated with dense, tiny granular tubercles, and aligned with six pairs of separated, large, and circular branchial openings. This condition is different from that of osteostracans, in which the oralobranchial fenestra is covered by numerous minute scales or larger dermal platelets, and the branchial openings are slit-shaped and covered by small skin flaps somewhat like those of elasmobranchs. However, the branchial openings of galeaspids and osteostracans are both located ventrally as in modern rays, indicating a benthic lifestyle dwelling on sandy or muddy substrates in a quiet marine environment.

Key words: Qujing, Yunnan, Early Devonian, eugaleaspiform, Nochelaspis

摘要：

基于在云南曲靖西山村组两个不同产地发现的新材料,对最大的真盔甲鱼类漫游憨鱼(Nochelaspis maeandrine )进行了再描述。憨鱼属(Nochelaspis )与同一层位产出的云南盔甲鱼属(Yunnanogaleaspis )最为相似,但与后者明显不同的是,憨鱼属具有裂隙形的中背孔(长与宽之比大于6), 更强壮的内角,粗大的星状纹饰,以及具锯齿的中背孔和头甲边缘。漫游憨鱼的新材料提供了头甲腹面的关键形态学信息：口鳃窗被一个大的外骨骼腹片覆盖,该腹片上装饰着致密细小的瘤点,边缘排列有6对独立的圆形大鳃孔,这些鳃孔由腹片和腹环共同形成。盔甲鱼类的这种情况明显不同于骨甲鱼类,后者的口鳃窗被许多小嵌片或大一些的膜质小骨片覆盖,鳃孔呈裂隙状,并被小皮瓣覆盖,类似于现生的板鳃类。盔甲鱼类和骨甲鱼类的鳃孔与现生的鳐类一样,都开口于腹面,指示它们均为底栖鱼类,生活在具泥沙质基底的安静滨海环境中。

关键词: 云南曲靖, 早泥盆世, 真盔甲鱼类, 憨鱼属

CLC Number:

Q915.861

MENG Xin-Yuan, ZHU Min, GAI Zhi-Kun. Redescription of Nochelaspis maeandrine ,the largest eugaleaspiform from the Lower Devonian of Qujing, Yunnan. Vertebrata Palasiatica, 2021, 59(4): 257-272.

孟馨媛, 朱敏, 盖志琨. 2021, 59(4): 257-272, 云南曲靖下泥盆统最大真盔甲鱼类漫游憨鱼再描述. 古脊椎动物学报.

Figures/Tables 7

Fig. 1 Geological setting of Nochelaspis maeandrine A. location map of the two fossil sites in Qujing, Yunnan, Southwest China;B. fish-bearing lithological column in Qujing (revised from Cai et al., 2020; Jiang et al., 2021)

Fig. 2 Photographs of the holotypes of Nochelaspis maeandrine (A) and Yunnanogaleaspis major (B) from the Xishancun Formation in Qujing, Yunnan, China A, B. external mould of nearly complete headshields in ventral view: A. IVPP V 10106, B. GMC V 1734 Abbreviations: c. cornual process; dcm. dorsal commissure; ic. inner cornual process; ifc. infraorbital canal; ldc. lateral dorsal canal; ltc. lateral transverse canal; mdc. median dorsal canal; md.o. median dorsal opening; orb. orbital opening; pi. pineal fossa; se. serrated edge of the median dorsal opening; soc2. posterior supraorbital canal

	N. maeandrine		Y. major
	IVPP V 10106	V 26124.2	GMC V 1734
Maximum length of the headshield	127.0	–	112
Maximum width of the headshield	158.5	–	–
Length of the headshield in midline	78.0	–	78.0
Maximum diameter of the orbital opening	10.0	9.0	9.8
Distance between the orbital openings	33.0	32.8	31.3
Long axis of the median dorsal opening	24.5	21.6	18.0
Short axis of the median dorsal opening	2.4	2.4	3.4
Long axis of the pineal fossa	–	–	1.3
Short axis of the pineal fossa	–	–	0.9
Length of the pre-pineal region	–	–	45.5
Length of the post-pineal region	–	–	32.5
Distance between paired inner cornual processes	49	–	–

Fig. 3 Photographs of Nochelaspis maeandrine IVPP V 26124.2, 3 from the dark grey sandy mudstone of the Xishancun Formation in Qujing, Yunnan, China A, B. a nearly complete headshield, V 26124.2: A. in dorsal view, B. in ventral view to the anterior part, showing the oral fenestra; C. close-up of median dorsal opening (box region of Fig. 3A); D. the complete cornual and inner cornual process of the headshield, V 26124.3, in ventral view; E. close-up of serrated margin of the headshield (box region of Fig. 3D). Abbreviations see Fig. 2 plus or.f. oral fenestra; vr. ventral rim

Fig. 4 Photographs of Nochelaspis maeandrine , IVPP V 26124.1, 4 from the light-yellow pelitic siltstone of the Xishancun Formation in Qujing, Yunnan, China A. an incomplete headshield (left-half part) of N. maeandrine , V 26124.1 associated with an incomplete headshield of Laxaspis cf. L. qujingensis , in dorsal view; B. close-up of two branchial openings (box inset 1 of Fig. 4A); C. close-up of the ornamentation on the ventral plate (box inset 2 of Fig. 4A), showing small, dense granular tubercles; D. close-up of the ornamentation on the headshield (box inset 3 of Fig. 4A), showing large, stellate tubercles; E. cornual process and inner cornual process of the headshield, V 26124.4 Abbreviations see Figs. 2, 3 plus br.f. branchial fenestra; br.o. branchial opening; vp. ventral plate

Fig. 5 Restoration of Nochelaspis maeandrine in dorsal (A) and ventral (B) views Abbreviations see Figs. 2-4 plus m. mouth

Fig. 6 The branchial apparatuses in fossil and living craniates A. photograph of Hanyangaspis guodingshanensis Pan & Liu, 1975, GMC V 1823, in ventral view;B. photograph of Shuyu zhejiangensis Gai et al., 2011; Pan, 1986a, IVPP V 14334.11, in ventral view;C. photograph of Yunnanogaleaspis major Pan & Wang, 1980, counterpart of GMC V 1734, in ventral view;D. drawing of Polybranchiaspis liaojiaoshanensis Liu, 1965 (modified from Janvier, 1996);E. drawing of Astraspis desiderata Bryant, 1936 (modified from Kardong, 2015); F. drawing of a generalized cornuate osteostracan, partly based on specimens of ‘Cephalaspis ’ cradleyensis Stensiö, 1932(modified from Janvier, 1996); G. drawing of the pteraspidiform heterostracan Doryaspis nathorsti (redrawn according to Pernègre, 2002, 2005; Gai et al., 2018); H. drawing of an Atlantic hagfish Myxine glutinosa (from Bloch and Schneider, 1801); I, J. drawing of the marine lamprey Petromyzon marinus : I. skeletal elements (modified from Oisi et al., 2013), J. external morphology; K. drawing of chondrichthyan Squalus acanthias (J, K from De Iuliis and Pulerà, 2007) Abbreviations see Figs. 2-5 plus avp. anterior ventral plate; br.a. branchial arch; br.p. branchial plate; br.s. branchial slit; gp. gill pouch; or.p. oral plate; tr.r. trematic ring

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