First record of Saurichthys (Actinopterygii: Saurichthyidae) from the Late Triassic of eastern Paleo-Tethys

doi:10.19615/j.cnki.2096-9899.221013

Abstract

Abstract:

The saurichthyiform fishes, characterized by a pointed rostrum and a streamlined long and slender body plan, ranked among the top predators of the ichthyofauna in the Early Mesozoic oceanic ecosystem. In a cosmopolitan pattern, these fishes rapidly radiated after the end-Permian mass extinction (EPME) and diversified morphologically and ecologically during the Middle Triassic. Thereafter, they seemingly showed a notable shrinkage from a global distribution to an occurrence basically restricted to the western Paleo-Tethys realm since the Late Triassic. Specifically, there is no saurichthyiform fossil record so far from the marine Late Triassic of South China (eastern Paleo-Tethys), where contrastingly they were highly diversified in stratigraphically older Lagerstätten (Middle Triassic Panxian-Luoping and Xingyi biotas). Here we report the discovery of Saurichthys taotie sp. nov. from the Guanling biota of Guizhou and Yunnan provinces, southwestern China. This new species is a medium-sized Saurichthys featured by subtriangular subopercles ornamented with densely arranged vertical striae, faint ornamentation on the posterior part of the skull roof, and strong longitudinal ridges decorating the anterodorsal surface of the rostrum. By marking its own group’s first occurrence in the Late Triassic of eastern Paleo-Tethyan province, Saurichthys taotie suggests that the saurichthyiform fishes were actually much more widespread than previously thought during that geological stage when they showed a considerable decline in the diversity. By still possessing some features previously only seen in its Early Triassic congeners elsewhere, Saurichthys taotie sheds new light on the evolutionary and paleobiogeographical history of saurichthyiform fishes.

Key words: Guanling biota, Guizhou, Yunnan, eastern Paleo-Tethys, Late Triassic, Saurichthys

摘要：

龙鱼类具尖吻和流线型的细长体型，是中生代早期海洋鱼群中的顶级捕食者。经历晚二叠世生物大绝灭(EPME)后，龙鱼类在全球范围内快速辐射，并于中三叠世时期在形态特征及适应策略上发展出可观的多样性。先前的化石记录显示，曾经全球广布的龙鱼类似乎自晚三叠世开始收缩至西特提斯洋。当时海生脊椎动物多样性的热点——东特提斯洋区中国华南晚三叠世海相地层中迄今尚无龙鱼类的记录，与此呈鲜明对照的是，该地区更低层位(如中三叠世盘县-罗平生物群和兴义生物群)的数个化石库(Lagerstätten)却保存有高度多样化的龙鱼类化石。报道了产自中国西南地区(黔西南和滇东地区)晚三叠世早期的关岭生物群的龙鱼属(Saurichthys)一新种——饕餮龙鱼(Saurichthys taotie sp. nov.)。饕餮龙鱼体型中等，其主要特征有：下鳃盖骨(subopercle)近三角形且外侧具密集纵纹，颅顶后部纹饰较弱，吻部前端背缘发育显著的纵嵴。作为龙鱼类在晚三叠世东特提斯洋区的首次记录，饕餮龙鱼的发现说明当时这一类群的多样性虽然在全球范围内呈现显著的下降，但它们的地理分布实际上比先前的认识广阔得多。此外，饕餮龙鱼保留了一些此前仅见于早三叠世同类的特征，为认识龙鱼类的演化和生物地理学历史带来新的思考。

关键词: 关岭生物群, 贵州, 云南, 东特提斯洋, 晚三叠世, 龙鱼类

CLC Number:

Q915.862

FANG Geng-Yu, SUN Yuan-Lin, JI Cheng, WU Fei-Xiang. First record of Saurichthys (Actinopterygii: Saurichthyidae) from the Late Triassic of eastern Paleo-Tethys. Vertebrata Palasiatica, 2023, 61(1): 1-16.

房庚雨, 孙元林, 季承, 吴飞翔. 2023, 61(1): 1-16, 晚三叠世东特提斯洋龙鱼属(Saurichthys) (Actinopterygii: Saurichthyidae)的首次记录. 古脊椎动物学报.

Figures/Tables 7

Fig. 1 Geographic sketch map of the studied fossil localities; photographs of the Longbozi Outcrop, and coexisting fossils A. sketched location map, red pentagram: Longbozi outcrop (Longbozi Village), Fuyun County, Qujing City, Yunnan Province; red square: Xinpu Town, Guizhou Province; B, C. aerial photo (B) and fossiliferous layers (C) of the Longbozi outcrop, GPS in the center of the image is 15 cm long; D-F. photographs of co-occurring fossils from the Longbozi outcrop: D. IVPP V31228, hollow arrows indicate bivalves (Halobia sp.), and white arrows indicate Trachyceras sp., scale bar = 20 mm; E, F. Trachyceras multituberculatum collected from Longbozi outgroup, in lateral (E) and ventral (F) views, scale bars = 5 mm

Fig. 2 Measurement conventions in current study

Fig. 3 Saurichthys taotie sp. nov. from the Guanling biota (Late Triassic), eastern Paleo-Tethys A, B. photograph (A) and line drawing (B) of the holotype IVPP V31228; C. the close-up of the anterior length of the rostrum in A; D. the CL image of a length of the rostrum and the teeth covered by the matrix in A;E. photograph of the paratype IVPP V31229; F, G. close-up image (F) and line drawing (G) of the neural arches preserved in E, black arrows point the foramina in the inner side of the neural arches, which are possibly associated with the spinal nerves or vessels (Wu et al., 2009; 2011; 2015) Scale bars equal 20 mm in A, B and E, 5 mm in C and D, and 2 mm in F and G Anatomical abbreviations: ang. angular; art. articular; de. dentary; dpt.l. left dermopterotic; dpt.r. right dermopterotic; dsph. dermosphenotic; en1,2. anterior and posterior external nares; enpt. entopterygoid;fr.l. left frontal; ioc. infraorbital sensory canal; i.sop.r. the imprint of the right subopercle; mx. maxilla;na. neural arch; naao. nasaloantorbital; pa. parietal; q. quadrate; ropm. rostropremaxilla; soc. supraorbital sensory canal; sop.l. left subopercle; sop.r. right subopercle; t. a tooth; ?. unidentified structure

Table 1 Meristic characters of Saurichthys taotie sp. nov.

		IVPP V31228	IVPP V31229
Measurement (mm)	Skull length (L_sk)	181.5	~247.7
	Mandible length (L_mand)	163.0	220.4
	Skull depth (D_sk)	~24	~35
	Rostrum length (L_ro)	~124	~157.5
	Postorbital length (L_po)	~26	~37
	Cheek depth (D_ch)	~12	~18
	Subopercle length (L_sop)	18.5	~27
	Subopercle depth (D_sop)	19.1	~29
Proportion (%)	L_ro/L_mand	76.1	71.5
	L_po/L_mand	15.95	16.8
	L_po/L_ro	21.0	23.5
	D_sk/L_sk	13.2	14.1
	D_ch/L_po	46.1	48.6
	L_sop/D_sop	96.9	93.1

Fig. 4 Photographs of the subopercles of Saurichthys taotie sp. nov. (IVPP V31228) from the Guanling biota (Late Triassic), eastern Paleo-Tethys A. left subopercle; B. imprint and remaining parts of the right subopercle. Scale bars = 5 mm

Fig. 5 Comparison of the skulls of some known saurichthyiform fishes from the Middle to Late Triassic of Yunnan and Guizhou, China A. Saurichthys taotie sp. nov.; B. S. dawaziensis (Wu et al., 2009); C. S. yangjuanensis (Wu et al., 2015); D. S. spinosa (Wu et al., 2018); E. S. yunnanensis (Zhang et al., 2010); F. Sinosaurichthys longipectoralis (Wu et al., 2011); G. Saurichthys sp. from the Ladinian Xingyi biota, southwestern Guizhou Province (personal observations); H. Yelangichthys macrocephalus (Wu et al., 2013) Gray shadows highlight the subopercles. Scale bars equal 2 mm in D and 10 mm in other illustrations

Fig. 6 Paleogeographical distribution of Saurichthys in the Late Triassic Paleogeographic map adopted from Scotese (2014), records of Saurichthys mostly adopted from Romano et al. (2012) with minor modification Fossil records from the marine deposits (red dots): 1. Saurichthys taotie sp. nov., Guizhou and Yunnan provinces, China; 2. Saurichthys? sp., Svalbard, Norway; 3. S. irregularis, Württemberg, Germany; 4. S. striolatus (Carnian), Friuli-Venezia Giulia, Italy; 5. S. calcaratus, Lower Austria, Austria; 6. Saurichthys sp., Catalonia, Spain; 7. S. deperditus, Campania, Italy; 8. Saurichthys sp. (Norian), Friuli-Venezia Giulia, Italy; 9. S. deperditus, S. seefeldensis, Saurichthys sp., Lombardy, Italy; 10. S. seefeldensis, Tryol, Austria; 11. S. deperditus (= S. “krambergeri”), Upper Austria, Austria; Fossil records from freshwater deposits (yellow diamond): 12. Saurichthys sp., Junggar Basin, Xinjiang, China (Liu and Wei, 1988); 13. S. orientalis, Madygen Formation, Southwestern Kyrgyzstan (Kogan et al., 2009); 14. Saurichthys? sp., Greenland (Jenkins et al., 1994); 15. Saurichthys sp., Arizona, USA (Kligman et al., 2017); 16. S. huanshenensis (with questionable age), Shaanxi, China (Chou and Liu, 1957)

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