Beijing, 10 Oct (Zhongxin Net) -- Following the discovery of the "Jiujiang Jiangxia fish" in Jiujiang, Jiangxi Province in May this year, a research team led by researcher Gai Zhikun of the Institute of Vertebrate Paleontology and Paleoanthropology (Institute of Paleovertebrate Paleontology) of the Chinese Academy of Sciences recently found another "brother" of the 3-million-year-old Jiangxia fish -- the "Rong's Jiangxia fish" in the Tarim Basin of Xinjiang, ranging from less than 5 kilometers to more than 4,38 kilometers. This is also the team's first discovery of the oldest true armor fish in the region since the team first discovered the oldest multigill fish in the Tarim Basin in 200.

Ecological restoration map of Rong's river summer fish. Yang Dinghua/Painting

Fill in the last piece of the "puzzle"

Researcher Gai Zhikun, who is visiting Sweden, said in an interview with reporters on October 10 that the new discovery of Rong's Jiangxia fish fossils not only enriched the understanding of the diversity of armored fish in the early Silurian period of Xinjiang, but also had great significance for in-depth understanding of the radiation evolution, migration and spread of armored fish in the early Silurian period and its paleogeographical distribution pattern, and further proved that the Tarim Basin was very close to the South China Plate 3 million years ago, and may form the Tarim-South China Joint Plate. At the same time, this also adds the final "puzzle" to the contrast between the two major plates of Tarim and South China, the Silurian marine red layer.

Systematic location and geographical distribution of the "three brothers" of Jiangxia fish. Shi Aijuan, Liu Wenyu painting/painting

This important paleontological fossil discovery research achievement paper, guided by researcher Gai Zhikun, selected by the 2022 College Student "Science and Technology Innovation Program" of the Institute of Paleovertebrate of the Chinese Academy of Sciences, Liu Wenyu, an undergraduate student of Shandong University of Science and Technology, and Shan Xianren, a master's student of the Institute of Paleovertebrate of the Chinese Academy of Sciences, have recently been completed in the international professional academic journal Palaeogeography, Palaeoclimatology, Palaeoecology Published online.

Jiangxia fish "three brothers" have similarities and differences

Researcher Gai Zhikun, the corresponding author of the paper, said that armoured fish is an extinct jawless species unique to China and northern Vietnam, and the Rong's Jiangxia fish found in the Tarim Basin of Xinjiang belongs to the genus Jiangxia fish of the armoured fish suborder True armoured fish in the family Shuxia, and its genus name Jiangxia comes from the first species of the genus found in Jiangxia District, Wuhan, and the species name "Rong" was presented to Academician Rong Jiayu of Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences. In tribute to his outstanding contributions to the study of Silurian stratigraphy and paleogeography in China.

Photo of the fossilized Rong's Jiangxia fish (top) and its restoration of its head armor (bottom). Gai Zhikun/Photo, Gui Fang/Painting

At present, the genus Jiangxia fish includes three species: Houspine River Xia fish, Jiujiang Jiangxia fish and Rong's Jiangxia fish, these "three brothers" have a common feature, that is, the front end of the middle dorsal hole is not closed, so that the snout of the head armor looks as if it is split, that is, "split kiss". The new species of Rong's Jiangxia fish discovered this time is significantly different from the Houspine River Xia Fish and Jiujiang Jiang Xia Fish in that its head armor edge and the inner edge of the middle dorsal hole are densely covered with sharp jagged small thorns, which is of great significance for speculating the function of the middle dorsal hole widely found in armored fish. In addition, the Rong's Jiangxia fish is also significantly different from the Houspine River Xia Fish and the Jiujiang River Xia Fish in terms of head armor size and head armor decoration.

It has important biostratigraphic significance

Gai Zhikun said that the discovery of Rong's Jiangxia fish has important biostratigraphic significance, on the one hand, it expands the paleogeographical distribution of true armor fish from the South China plate to the Tarim plate, and on the basis of providing reliable fossil evidence for the comparison between the two underground red layers of Wuhan (Jiangxia) in Hubei Province and Jiujiang in Jiangxi, it also accurately compares the stratigraphic comparison between the Tarim plate and the South China plate to the level of species, indicating that the fish-bearing layers of the two plates can be compared completely.

On the other hand, from the existing fossil record, in the early Silurian period, 4 million years ago, Chinese armoured fish fossils were generally distributed along the edges of the ancient land of China and the ancient land of Yunnan and Guizhou, such as the "two brothers" of the Houthorn River summer fish and the Jiujiang River summer fish, which is less than 38 kilometers in a straight line, which indicates that the vast area of China, dominated by the Yangtze River basin, was a vast ocean - the Yangtze Sea at that time. The sudden appearance of the Rongshi Xia fish in the Tarim Basin, 200,4000 kilometers away, also made the research team further think about the relationship between the two major plates of South China and Tarim.

The scientific research team at the field fossil excavation site in the Tarim Basin in 2022. Zhao Ridong/Photo

Gai Zhikun pointed out that in the Silurian period, the three major plates of North China, South China and Tarim formed the main body of the ancient Chinese mainland, however, the paleogeographical location of these three plates and their relationship have always been controversial. Jiangxia fish, originally a fossilized armored fish unique to South China, was first discovered in the Tarim area, fully indicating that as early as 4 million years ago, biological communication between the two plates took place. Therefore, the Tarim plate and the South China plate should belong to the same paleo-faeogeographic region in the Silurian period, that is, the Tarim-South China fish zoogeographic fauna, and the two plates have a very close paleogeographical connection in the early Silurian period, and they are likely to coexist in the same warm and organic matter-rich paleosea basin environment.

As early as 2009, researcher Zhao Wenjin of the Institute of Paleospine of the Chinese Academy of Sciences proposed based on the appearance and stratigraphic sequence of fish stocks that the South China Plate and the Tarim Plate in the early Silurian period should be close enough in paleogeography and in the same shallow sea environment, and may even be combined to form the Tarim-South China Joint Plate.

Paleogeographical map of the Tarim Plate and the South China Plate. Shan Xianren, Liu Wenyu, Shi Aijuan/painting

"The first discovery of the Rong's Jiangxia fish in the Tarim Basin of Xinjiang further supports the existence of the Tarim-South China joint plate. It is precisely because of plate drift that the 'three brothers' (fossils) of Jiangxia fish, which originally lived in the same sea, are now thousands of miles apart. Gai Zhikun concluded. (End)