GEOGRAPHY

Yunnan is the first to find the 390 million-year-old Devonian multigill fish Oriental fish


Ecological Restoration Map of Oriental Fish (Painted by Yang Dinghua)

Fossil photographs of oriental fish and broad turtles (photo by Gai Zhikun) (A. orthographic specimen of the giant oriental fish; B. specimen of “Qujing oriental fish”; C. Qujing broad turtle (similar species) specimens, B, C have been wrongly classified as oriental fish genus)

Recently, Meng Xinyuan of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, under the guidance of researcher Gai Zhikun, published the latest research results of Devonian multigill fish online in the Journal of Paleontology.

The study reported for the first time the fossil of the multi-gill fish found in the Haikou group of the Devonian Eiffel period (about 390 million years ago) in Wuding County, northeast of Yunnan Chuxiong Yi Autonomous Prefecture, representing the largest known gill sac, with up to 45 pairs of gill sacs, more than 7 times the most primitive armor fish of the Silurian period.

Corresponding author Gai Zhikun told China Science Daily that the multiplication of gill sacs of armored fish has always been an unexplainable evolutionary phenomenon, and the new findings suggest that it may be an evolutionary response of armored fish to the recurrent marine hypoxia events of the early Devonian, and may be the secret of the survival of oriental fish to the Middle Devonian.

The new discovery is not only the first report of the fossil of the Middle Devonian armor fish in Yunnan Province, but also the fossil record of the second Middle Devonian armor fish in China so far, and extends the survival age of the oriental fish genus (Dongfangaspis) from the early Devonian Prague period (about 410 million years ago) to the Middle Devonian Eiffel period (about 390 million years ago), and extends back for about 20 million years, not only filling the geological gap of the carpaloids in the Middle Devonian in Yunnan region. It also increases our understanding of the radiation evolution and diffusion migration routes of armor fish during the Devonian Period, and is also of great significance for exploring the co-evolution of gill sac numbers in armor fish and the early Ames period ocean hypoxia event.

The oriental fish specimen studied this time, collected from the field to Mr. Wang Junqing’s rediscovery, has been sleeping in the underground herbarium for more than 30 years, and from the rediscovery to today’s official publication, it has been waiting for nearly 10 years.

The fossil oriental fish found this time preserves only part of the abdominal ring on the left side of the head carapace, but this is already the best preserved armor fish specimen in the Middle Devonian. The new specimen head armor is rounder, but only half preserved, a bit like the ancient Chinese lute, which only half exposed. Although incomplete, the new specimen has the typical characteristics of a multigill fish, that is, it has a large number of gill sacs (at least 37 pairs of gill sacs are preserved in the gill area), but based on the length of the abdominal ring and the width of each gill sac, it should have as many as 45 pairs of gill sacs as the giant oriental fish.

In addition, the preserved part of the specimen indicates that its ventral ring is wide and long, that it is a larger multigill fish, that the orbital foramen is large and rounded, has at least 3 contralateral transverse tubes, and that the cephalic carapace is decorated with small, dense granular protrusions, and these features, especially the number of gill sacs, indicate that they should belong to the genus Oriental fish. In contrast, the ventral rings of the broad turtle are wider, but unevenly distributed in an uneven distribution with a wide anterior cusp and posterior end, with 18 pairs of gill sacs; The abdomen of the multi-gill fish is narrower than that of the oriental fish, with only 12 pairs of gill sacs.

As for whether the specimen represents a new species of oriental fish, because the specimen does not preserve key information such as nostrils and orbitholes, the research team did not name the new species for the time being, but regarded it as a pending species of oriental fish, pending new discoveries in the future wild, and further research to determine.

Possessing the largest number of gill sacs in history, it may be the secret weapon that the Oriental fish has survived.

Early armor fish had a small number of gill sacs, such as true armor fish and Sulus Dayong fish, Shushui fish, etc., with only 6-7 pairs of gill sacs, which may represent the ancestral state of armor fish. The “multigill” (more than 10 pairs of gill sacs) of multi-gill fish began with radiation during the early Devonian Lochkov period, during which the number of gill sacs of armored fish was less than 20 pairs, such as 12 pairs of multi-gills and 18 pairs of broad turtles.

The increase in the number of gill sacs of armored fish was an evolutionary trend during the Silurian-Devonian period.

The vast majority of armored fish became extinct during the early Ems biological events, with only the Oriental fish having the largest number of gill sacs ever recorded, continuing into the Middle Devonians, which may be the secret to their survival from extinction events caused by lack of oxygen.

The research has been funded by the Strategic Pilot Science and Technology Special Project of the Chinese Academy of Sciences (Category B), the National Natural Science Foundation of China, and the Frontier Science Key Research Program of the Chinese Academy of Sciences. (Source: China Science Daily Cui Xueqin)

Related paper information:https://doi.org/10.19615/j.cnki.2096-9899.220613



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