Revision of two relic actinopterygians from the Middle or Upper Jurassic Karabastau Formation, Karatau Range, Kazakhstan

Abstract

Three hundred and forty-six articulated fossil specimens of two species from the Middle or Upper Jurassic Karabastau Formation of the Karatau Range (Kazakhstan, Asia) were studied to revise two little-known palaeonisciform fish: Pteroniscus turkestanensis and Morrolepis aniscowitchi. Detailed morphological analysis shows that P. turkestanensis, Daqingshaniscus longiventralis and Uighuroniscidae form a closely related group. They are far more distantly related to the Palaeoniscidae than previously inferred. The first detailed scanning electron microscopy of the unique scale cover of M. aniscowitchi is presented. Morrolepis is found to be devoid of denticles on the surface of the bones, scales and lepidotrichia—so far considered to be a key coccolepidid characteristic. However, it bears exceptionally robust lateral line scales. Comparison of the axial skeletons of M. aniscowitchi and Morrolepis andrewsi reveals their close affinities within Coccolepididae. The axial skeleton, despite its rare preservation in palaeonisciforms, may be taxonomically informative, at least at the family level. The Karatau palaeonisciforms, being among the youngest examples of basal actinopterygians (persisting in Asia through the late Mesozoic), possess a set of conservative morphological characters that suggest they were relictual taxa by Jurassic times, thus highlighting some freshwater systems as refuges for plesiomorphic taxa.

共研究了Karatau山脉（亚洲哈萨克斯坦）中或上侏罗统的两个种的三百四十六个铰合化石标本，其目的是修正两个鲜为人知的古鳕鱼型鱼类：Pteroniscus turkestanensis and Morrolepis aniscowitchi 。详细的形态学分析表明，P. turkestanensis、Daqingshaniscus longiventralis和Uighuroniscidae形成密切相关的群体。它们与古鳕鱼的关系比先前推断得还要远。本文还报道了对 M. aniscowitchi的独特鳞片所进行的首次详细电子显微镜扫描。 我们发现Morrolepis的骨骼、鳞片和lepidotrichia表面缺乏细齿，迄今为止这点被认为是粒鳞鱼的一个关键特性。然而，它具有极其坚固的侧线鳞。 M. aniscowitchi和Morrolepis andrewsi的轴向骨架的比较揭示它们在粒鳞鱼类之内的紧密的亲缘关系。中轴骨骼，尽管它的保存罕见，可能至少在科一级具有分类学信息。Karatau山脉的 古鳕鱼型鱼是基底辐鳍鱼（亚洲中生代晚期）的最年轻的例子，具有一系列保守特征，说明他们是侏罗纪的残余类群，从而显示作为祖征类群的避难所的一些淡水系统。

Key words:

• Coccolepididae
• evolution
• fish
• freshwater
• Palaeonisciformes
• anatomy.

Acknowledgements

I would like to thank the following people for their contributions to this study: Ilja Kogan (Techinische Universität Bergakademie, Freiberg), Carlo Romano (University of Zurich, Zurich), and to an anonymous reviewer for their kind improvements of the draft; Steve McLoughlin (the editor) for his patient corrections, helpful comments and literature; H.-P. Schultze (University of Kansas, Lawrence, Kansas) and M. Borsuk-Białynicka (Institute of Paleobiology PAS, Warsaw) for reading the manuscript, giving knowledgeable advice on systematics and anatomy, and providing access to rare literature; J. Dzik (Institute of Paleobiology PAS, Warsaw) for supplying the study material and supervising my research; H. Ishbaev Djangirovich (University of Tashkent, Tashkent) for identifying the type collections of Pteroniscus and Morrolepis; M. Véran and G. Clément (Muséum national d’Histoire naturelle, Paris), L. Steel, Z. Johanson and M. Richter (Natural History Museum, London) and R. Boettcher and D. Seegis (Staatliches Museum für Naturkunde, Stuttgart) for providing access to museum collections and an amicable atmosphere; P. Loubry (Muséum national d’Histoire naturelle, Paris) for supplying photographs of specimen MNHN1977_3.1; C. Kulicki (Institute of Paleobiology PAS, Warsaw) and Z. Banach (Jagiellonian University, Krakow) for their assistance with SEM and EDAX analyses; E.K. Sytchevskaya (Paleontological Institute, RAS, Moscow) for providing key information on the Russian collection of Karatau fossils and rare Russian publications; D. Miao (University of Kansas, Lawrence, Kansas) for supplying information on Chinese localities and also rare papers; A. López-Arbarello (University of Munich) for discussions and literature on South American sites; A. Skawina (University of Warsaw, Warsaw) for her helpful comments on the illustrations; P. Bernatowicz and M. Tałanda (University of Warsaw, Warsaw), and P. Skrzycki (Institute of Paleobiology PAS, Warsaw) for reading parts of this paper and for their useful comments and suggestions.