Galeaspids are an extinct group of Jawless Fish interpreted as stem-Gnathostomes (i.e. more closely related to modern jawed Vertebrates than to the living Lampreys and Hagfish), known from the Silurian and Devonian of China and Vietnam. The area around the city of Qujing in eastern Yunnan Province, China, is noted for the production of Late Silurian-Early Devonian Galeaspid fossils. Many of these were originally considered to have come from the Early Devonian Xitun Formation, but a re-evaluation of the location which produced them has led to the conclusion that they derive from the earlier Xishancun Formation, suggesting that these Fish became locally extinct in the Earliest Devonian.
In a paper published in the journal Vertebrata PalAsiatica on 20 June 2022, Sun Hao-Ran of the Institute of Geology and Geophysics of the Chinese Academy of Sciences, the Key Laboratory of Vertebrate Evolution and Human Origins at the Institute of Vertebrate Paleontology and Paleoanthropology, and the University of the Chinese Academy of Sciences, Gai Zhi-Kun and Cai Jia-Chen, also of the Key Laboratory of Vertebrate Evolution and Human Origins at the Institute of Vertebrate Paleontology and Paleoanthropology, and the University of the Chinese Academy of Sciences, and of the Center for Excellence in Life and Paleoenvironment, Li Qiang of the Research Center of Natural History and Culture at Qujing Normal University, and Zhu Min and Zhao Wen-Jin, again of the Key Laboratory of Vertebrate Evolution and Human Origins at the Institute of Vertebrate Paleontology and Paleoanthropology, the University of the Chinese Academy of Sciences, and the Center for Excellence in Life and Paleoenvironment, describe a Galeaspid Fish from an outcrop of the Xitun Formation close to Xitun Village (which lends its name to the formation) in Yunnan Province, China.
Map showing the fossil locality (A) and the Fish-bearing lithological column (B) in Qujing. Sun et al. (2022).
The new species is named Xitunaspis magnus, where 'Xitunaspis' is a combination of Xitun, plus 'aspis', meaning 'shield', in reference to the distinctive head shields of Galeaspid Fish (the suffix -aspis is commonly used for genera in this group), and 'magnus' means 'large'. The species is described from a complete headshield with associated mould, plus three incomplete headshields.
Photographs of Xitunaspis magnus from the Xitun Formation in Qujing. (A), (B) The external (A) and internal mould (B) of a nearly complete headshield, IVPP V 27400.1 (holotype); (C), (D) two incomplete headshields, V 27400.2 (C), V 27400.3 (D); (E) close-up of the median dorsal opening
of V 27400.3. (A) in ventral view; (B)–(E) in dorsal view; scale bars equal 10 mm
Abbreviations: c. cornual process; ifc. infraorbital canal; md.o. median dorsal opening; orb. orbital opening;
pi. pineal opening; ri. dermal ring encircling median dorsal opening;
spi. spine-like ridge on the dermal ring of median dorsal opening. Sun et al. (2022).
Xitunaspis magnus is a large Galeaspid Fish, with a headshield 103 mm in length and 146 mm in width. The rostral margin of the headshield is blunt, with narrow leaf-shaped cornual processes extending posterolaterally, giving it a crescent shape. It has a slit-like median dorsal opening extending posteriorly from between the orbital openings, which are rounded and high on the head. A sensory canal-system U-shaped median dorsal canals,
posterior supraorbital canals, infraorbital canals, lateral dorsal canals, and three pairs of lateral
transverse canals is present. The surface of the headshield is covered in large polygonal, flat-topping tubercles.
Reconstructions of Xitunaspis magnus in dorsal view. (A) 3D reconstruction of IVPP V 27400.4 based on Micro-CT scanning; (B) restoration of the headshield by Feng Mingjuan; (C) life restoration by Shi Aijuan; scale bars equal 10 mm. Sun et al. (2022).
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