In the evolutionary history of life, the Devonian period is often referred to as the "Fish Age". For nearly 60 years, the continuous discovery of Fossils of Silurian fish around the world has enabled people to push forward the "Fish Age" to the Silurian. The fossil record shows that the Silurian period was a key period in the evolutionary history of vertebrates, with jawless species flourishing, with all important taxa of jaws such as shieldfish, echinococcus, cartilaginous fishes and teleost fishes emerging and gradually developing. Silurian fish fossils not only provide key data and empirical evidence for a series of major topics in the history of life, such as the origin of jaws, the origin and early differentiation of jawed crown groups, but also provide a reliable paleoichthological basis for discussing the division and comparison of fish fossil strata and the study of fish paleozoological geography.
The Silurian Tatartag Formation and the Imukgan Tawu Formation in the Keping-Bachu region of the northwest edge of the Tarim Basin in Xinjiang are mainly a set of shallow sea-coastal-continental clastic deposits, with a relatively single lithology, a thickness of more than 1000m, and the color is mainly red, which is often called the red rock system by predecessors. Since 1988, when it was reported that the red rock system contained Chinese spiny fish, the discovery of a large number of armored fish and cartilaginous fish has made the Tarim Basin one of the important Silurian fish fossil production areas in China and even in the world. However, the Mostly Described Andrean Fishes in the region so far are mostly endemic armor fish, while there are few studies of the globally widespread and diverse cartilaginous fish Mongolian Fish. In-depth research on Mongolian fish and Chinese spiny fish in the Tarim region 430 million years ago not only further enriched the diversity of Silurian fish, but also had great significance for exploring the phylogenetic framework of cartilaginous fish and even early jaws, regional comparison of Fish-bearing strata in the Silurian period of China, and in-depth study of paleozoological geography.
Recently, the Public Science Library - PLOS One published online a newly completed sino-British cooperation team led by Zhu Min, a researcher at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, on the early-surviving cartilaginous fish in the Tarim Basin of Xinjiang.
This achievement is mainly based on the accumulation of a large amount of fossil materials in the early stage, using research methods and methods such as microcomputer tomography, electron microscopy scanning and paleohistological sectioning, in-depth study of a large number of cartilaginous fish scales and spine fossil materials from the Keping-Bachu region of the northwest edge of the Tarim Basin in Xinjiang, and a large number of cartilaginous fish scales and spine fossil materials in the Imugan Tawu group, and describe in detail 8 of them, including 4 new genera (Taklamakan fish, Talikwa iron fish, small sea fish and Yuan's fish, Fig. 1), and establish a new order - Chinese spiny fish. The results of the in-depth discussion showed that 7 genera, such as Taklamaka, had typical Mongolian fish scale characteristics - the scale crown had multiple odontode rows, while the Yuan's fish showed the scale characteristics of some basal cartilaginous fish (such as seretolepis, parexus, etc.) in the early Devonian period - the scale crown had only a single row of dentate units (Fig. 2). The paleo-histological studies of Chinese spiny fish have shown that this taxon should be located in the basal position of cartilaginous fish; the discovery of a large number of Silurian cartilaginous fish in the Keping-Bachu region of Xinjiang, Mongolian fish and Chinese spiny fish, enriched the diversity of Silurian cartilaginous fish and expanded the paleogeographic distribution of Mongolian fish, and Mongolian fish and Chinese spiny fish were also found and reported in the Silurian Xiushan Group in South China, which further confirmed that South China and Tarim had a close paleogeographic connection between the early Silurian Trichi period. The Silurian strata and their ages can be well compared, and the distribution range of the early Silurian Zhangjiajie fauna developed in South China has been extended to the Tarim region of Xinjiang.
Zhao Wenjin, a researcher at the Institute of Paleovertebrates of the Chinese Academy of Sciences, and Plamen S. andreev, Pharmone S. andreev of Qujing Normal University, are the co-first authors of the paper, which is supported by the Strategic Pilot Science and Technology Special Project of the Chinese Academy of Sciences (Class B and Class A), the National Natural Science Foundation of China, and the Frontier Science Key Research Project of the Chinese Academy of Sciences.
Figure 1: Four new genera of early Chiliu cartilaginous fish in the Keping-Bachu region of Xinjiang: (1) Taklamakanolepis, (2) Tielikwa ironfish tielikewatiepis, (3) Xiaohaizilepis, and (4) Yuan's fish yuanolepis
Figure 2: Evolutionary characteristics of early-Epiphytic cartilaginous fish in the Keping-Bachu region of Xinjiang (1) and spatial distribution of fossil sites and fish-bearing layers (2)
Source: Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences