Find out! Grass carp originated in western China 33 million years ago

Grass carp is one of the four major freshwater carps in my country. It is popular among foodies for its delicious meat. So, do you know when and where grass carp originated?

On November 2, the reporter learned from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences that researchers from the institute and other units conducted comparative studies on pharyngeal tooth fossils of two extinct grass carp-like genera and species and two extinct grass carp species collected from Inner Mongolia, Qinghai, Jiangsu and other places, as well as pharyngeal tooth fossils of modern grass carp, and found that grass carp may have originated from a carnivorous fish in western China in the early Oligocene 33 million years ago. At that time, although the climate in western China may have been drier than in the east, it still had suitable climatic conditions for the growth of grass carp. Modern grass carp may have been formed in the Pliocene 5.3 million years ago. The relevant research results were published as a cover article in the English version of "Science China: Earth Sciences".

The cover of the article published in Science China: Earth Sciences. Photo provided by the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences

The history of grass carp being eaten in China can be traced back to the Shang Dynasty. Its current species are naturally distributed in the eastern region of China. It is called "pioneer" because it can quickly clear various grasses in the water.

Grass carp has unique comb-shaped pharyngeal teeth. The surface of grass carp pharyngeal teeth is enamel, which is very hard. The old pharyngeal teeth will wear out during the continuous feeding, and then new pharyngeal teeth will grow out to replace them. Su Ruifeng, an associate researcher at the Beijing Institute of Life Sciences of the Chinese Academy of Sciences, said: "The worn-out pharyngeal teeth are buried in the strata and have become very precious materials for our study of the evolution of carp fish."

"After studying the pharyngeal tooth fossils of two extinct grass carp-like genera and species and two extinct grass carp species found in many places, we speculate that grass carp originated from a carnivorous fish in western China in the early Oligocene 33 million years ago. At that time, there was a temperate grassland environment there, which is quite different from the habitat of grass carp today," said Su Ruifeng.

According to the grass carp-like or grass carp fossils discovered so far, from the late Oligocene to the Miocene, grass carp spread eastward and migrated throughout western, eastern and northern China, with a much wider distribution range than the modern grass carp. Since the Pliocene 5.3 million years ago, with the strengthening of the Qinghai-Tibet Plateau, the formation of large rivers flowing eastward into the Pacific Ocean in East Asia, and the strengthening of the Asian summer monsoon, the distribution of grass carp was eventually limited to the new environment on the east coast of the Pacific Ocean, evolving into modern species and forming the current living and breeding habits.

In Su Ruifeng's view, the study of the pharyngeal tooth fossils of grass carp has broadened the knowledge and understanding of the evolution of carp fish unique to East Asia in time and space. Combined with the living and reproductive habits of grass carp and the mammalian groups unearthed at the same location, it can reflect the climate and water environment characteristics of the land site at that time to a certain extent.

Among the major rivers in eastern China, the Heilongjiang and Yellow River systems have many species of fish, and grass carp is one of them. However, there is no record of grass carp in the Liaohe River system between these two major rivers. Researchers believe that it is very likely that grass carp was once distributed in the Liaohe River when the Nenjiang River was still the upper reaches of the Liaohe River. In the Quaternary Period, Changchun City and its surrounding areas between the Nenjiang River and the Liaohe River were uplifted due to neotectonic movements, and the upper reaches of the ancient Nen-Liao River basin were seized by the Songhua River, a major tributary of the Heilongjiang River, thus bringing many fish species, including grass carp, to the Heilongjiang River in the north. When the Liaohe River separated from the Nenjiang River upstream, the water volume and length of the Liaohe River were no longer suitable for the survival and reproduction of grass carp.

Su Ruifeng said that the evolution of grass carp shows that during the Oligocene, the climate near Sanshenggong in western China was a bit dry and cold but still warmer than it is today; during the Miocene, the climate in central Inner Mongolia was also warmer and more humid than it is today; and it was not until the Pliocene that the climate and aquatic ecological environment in East Asia became similar to those of modern times.

◎ Science and Technology Daily reporter Lu Chengkuan

Source: Science and Technology Daily

Editor: Liu Yiyang

Review: Yue Liang

Final review: Liu Haiying