Taxonomic revision of Sinoeugnathus kueichowensis (Halecomorphi, Holostei) from the Middle Triassic of Guizhou and Yunnan, China

doi:10.19615/j.cnki.2096-9899.230703

Abstract

Abstract:

The previously alleged ‘eugnathid amiiform’ Sinoeugnathus kueichowensis is a small-sized halecomorph from the Middle Triassic (Ladinian) marine deposits of Guizhou and Yunnan, China. A morphological redescription and taxonomic revision of this taxon are provided based on a detailed examination of the holotype and 15 new specimens. Studies of these specimens revealed some morphological details previously undescribed or misidentified for this taxon, including a hatchet-shaped antorbital, two broad suborbitals, a sensory canal in the maxilla, and three pairs of extrascapulars. For the first time, Sinoeugnathus was incorporated into an analysis of halecomorph phylogeny, and the results recover it as the sister taxon of the Anisian Subortichthys from Luoping, Yunnan, and both are grouped with two Ladinian genera Allolepidotus and Eoeugnathus from the Monte San Giorgio area into a monophyletic group (namely Subortichthyidae fam. nov. herein) at the base of Ionoscopiformes. This taxonomic reassessment of Subortichthys provides new insights into the phylogeny and paleogeographic evolution of Ionoscopiformes.

Key words: Guizhou and Yunnan, Middle Triassic, Ionoscopiformes, Halecomorphi, osteology, phylogeny

摘要：

小型近鲱形类(Halecomorphi)贵州中华真颌鱼(Sinoeugnathus kueichowensis)发现于中国云贵地区中三叠世拉丁期海相地层中，曾被归入弓鳍鱼目(Amiiformes)真颌鱼科(Eugnathidae)。基于模式标本和15块新标本的详细观察，对该属种进行了重新描述和分类学修订。对这些标本的研究揭示了该属种在早前研究中一些未被描述或识别错误的形态特征，包括斧状的眶前骨，两个宽大的次眶骨，上颌骨具有感觉管和三对额外肩胛骨。首次将中华真颌鱼纳入近鲱形类分支系统学研究中；结果显示，中华真颌鱼与云南罗平安尼期的复兴鱼(Subortichthys)构成姐妹群，两者与欧洲圣乔治山地区拉丁期的Allolepidotus和始真颌鱼(Eoeugnathus)一起组成预言鱼目(Ionoscopiformes)底部的一个单系群(命名为复兴鱼科)。中华真颌鱼的分类学修订为了解预言鱼目的系统发育关系和古地理演化提供了新的信息。

关键词: 云贵地区, 中三叠世, 近鲱形类, 预言鱼目, 骨骼学, 系统发育

CLC Number:

Q915.862

FENG Dong-Hao, XU Guang-Hui, MA Xin-Ying, REN Yi. Taxonomic revision of Sinoeugnathus kueichowensis (Halecomorphi, Holostei) from the Middle Triassic of Guizhou and Yunnan, China. Vertebrata Palasiatica, 2023, 61(3): 161-181.

冯东昊, 徐光辉, 马昕莹, 任艺. 2023, 61(3): 161-181, 云贵地区中三叠世近鲱形类贵州中华真颌鱼(Sinoeugnathus kueichowensis)的分类学修订. 古脊椎动物学报.

Figures/Tables 10

Fig. 1 Holotype, two new specimens and reconstruction of Sinoeugnathus kueichowensis A. IVPP V2433 (holotype); B. V24315; C. V30784; D. reconstruction

Table 1 Measurement data of 11 specimens of Sinoeugnathus kueichowensis (mm)

Specimen	SL	HL	BD	TL	PVL	PDL	PAL
V2433	53.00	19.35	21.51	66.41	29.79	-	40.40
V19007	66.20	20.88	23.16	83.28	-	40.16	52.24
V24315	64.22	20.94	26.92	82.56	35.18	41.70	49.66
V24316	52.20	18.98	22.48	63.68	29.00	29.28	40.32
V24317	58.66	20.40	22.24	73.06	33.92	37.90	45.10
V24320	65.40	22.74	25.00	83.06	-	40.14	49.24
V30784	69.58	22.12	23.42	87.54	37.44	39.52	52.24
V30786	59.68	19.06	22.86	70.78	34.16	37.46	46.38
V30787	61.32	21.18	22.36	69.12	31.52	35.98	44.14
V30789	60.50	22.04	21.80	75.66	31.32	-	44.46
V30790	56.56	21.44	21.72	74.88	30.50	37.52	42.92

Fig. 2 Photograph (A) and line-drawing (B) of skull and pectoral girdle of Sinoeugnathus kueichowensis, IVPP V24315

Fig. 3 Photograph (A) and line-drawing (B) of skull and pectoral girdle of Sinoeugnathus kueichowensis, IVPP V30784

Fig. 4 Photograph (A) and line-drawing (B) of skull and pectoral girdle of Sinoeugnathus kueichowensis, IVPP V30785

Fig. 5 Cranial bones of Sinoeugnathus kueichowensis A. IVPP V24315; B. X-ray computed tomography of A, showing both the quadrate symplectic condyles for the jaw hinge; C. V30785; D. X-ray computed tomography of C, showing the hyomandibula and the foramen for the hyomandibular trunk of facial nerve (VII)

Fig. 6 Fins of Sinoeugnathus kueichowensis, IVPP V24315 A. left pectoral fin; B. left pelvic fin; C. dorsal fin; D. caudal fin; E. anal fin

Fig. 7 Complete specimen and lateral line scales of Sinoeugnathus kueichowensis, IVPP V30785 A. complete specimen; B. scales in predorsal region with arrow showing pore of additional lateral line; C. main lateral line scales in posterior flank region with arrows showing pores of lateral line

Fig. 8 Strict consensus of 48 most parsimonious trees illustrating the phylogenetic relationships of Sinoeugnathus within the Neopterygii Tree length = 661 steps; consistency index (CI) = 0.4115; retention index (RI) = 0.7665 Digits above nodes indicate Bremer decay indices. For character descriptions and codings for the sampled taxa, see the online supplementary material

Table 2 Measurements for eight specimens of Triassic ionoscopiforms (mm)

Species	MXL	MDL	HL	MXL/MDL	MDL/HL	SL	Specimen
Sinoeugnathus kueichowensis	13	15	22	0.87	0.68	69.6	IVPP V30784
Subortichthys triassicus	17	19	28	0.89	0.68	72	IVPP V20680
Allolepidotus bellotti	15.5	16.5	26	0.94	0.63	85	MCSNIO P647
Eoeugnathus megalepis	21	25	37	0.84	0.68	98	PIMUZ A/I 1964
Panxianichthys imparilis	20	27	50	0.74	0.54	159	IVPP V19971
Aisalepidotus shingyiensis	36	48	91	0.75	0.53	273	IVPP V23010
Robustichthys luopingensis	14	24	45	0.62	0.54	140	IVPP V18568
Robustichthys luopingensis	-	53	100	-	0.53	360	IVPP V20414

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