Research progress on evolution and spatial distribution of grass carp throat teeth since the Cenozoic

(A1-3) Sansheng Gongde made fish (new genus and new species)
.
(Photo courtesy of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences)

Recently, "Science in China: Earth Sciences" (English version) published a cover article titled "The Spatiotemporal Distribution Patterns of New Genera and Species of Grassfish Pharyngeal Tooth Fossils and Their Origin and Evolution and Paleoenvironmental Significance"

Grass carp is one of the famous "four major home fishes" in China, and its history of being eaten can be traced back to the Yin and Shang era
.
It is naturally distributed in the eastern part of our country

The evolution of grass fish pharyngeal teeth

The unique comb-shaped pharyngeal teeth of grass carp have been found in many strata in China since the Cenozoic
.
Through further research, it is found that comb-shaped pharyngeal teeth with ridges and grooves on the front and back of the tooth crown have appeared in the Early Oligocene strata 30 million years ago, although they are obviously different from the shape of modern grass carp pharyngeal teeth

So far, comb-shaped pharyngeal teeth have appeared in 22 sites in the early and late Oligocene, Early Miocene, Middle Miocene, Late Miocene, Pliocene, Pleistocene, and paleohuman sites
.

The research team found that the throat tooth fossils from two sites in the Oligocene represented two relatively ancient extinct species, and established the Sansheng Gongde fish of the genus Dezaoia and Liu of the genus Euphorbia.
The beginning of grass carp
.

The Sansheng Gongde fish from the Sansheng Gong Lower Oligocene Ulan Bragg Formation in Hangjinhou Banner, Inner Mongolia.
The ridges and grooves on the side of the tooth crown are relatively short, the top is curved and enlarged, the chewing surface is narrow and long and straight, and the end of the ridge The tip makes the edge of the chewing surface jagged
.
This jagged edge of the chewing surface is common in young grass carp just erupting teeth, but it has not been found in the pharyngeal teeth of adult grass carp

The first grass carp of the genus Liu's grass carp was collected from the Andi Upper Oligocene Dongying Formation in Hebei Province.
Its throat tooth shape is closer to that of existing grass carp, but the teeth are thicker and shorter, and the number of ridges on the front and back of the tooth crown is small and short.
The outer end of the chewing surface seems to turn later.
The fossils are from the Upper Oligocene and represent the extinct species of grassy fishes
.

In addition, a large number of throat teeth collected from the Miocene represent two extinct species of the genus Ctenopharyngodon, C.
xiejiaensis and C.
orientalis
.
The Xiejia grass carp throat teeth of the Xiejia Formation of the Huang Middle-Lower Miocene in Qinghai have both the main row of teeth and the second row of teeth

However, compared with existing grass carp pharyngeal teeth, Xiejia grass carp pharyngeal teeth have thicker crowns, thicker, shorter, and less ridges.
The stalks of the teeth are not significantly thinner at the boundary between the crowns and the grooves between the ridges.
It is wider than grass carp, and the ridges on the front and back sides are almost perpendicular to the chewing surface
.
The oriental grass carp comes from the early Miocene Xiacaowan Formation in Sihong, Jiangsu.

However, the morphology of these pharyngeal teeth is still significantly different from that of grass carp, such as the number of ridges and grooves are still significantly smaller, and the length is also significantly shorter
.
Since the Pliocene, the grass carp pharyngeal teeth appearing in various layers are completely consistent with the modern grass carp, indicating that the modern grass carp has formed since the Pliocene

Spatial and temporal distribution of grass carp and grass carp

The study reported on the two extinct genera and species of grass carp and two extinct species of grass carp, as well as modern grass carp pharyngeal tooth fossils, which broadened scientists' knowledge and understanding of the evolution of endemic carps in East Asia in terms of time and space
.
Combining their living and breeding habits and the mammals unearthed at the same location can reflect the climate and water environment characteristics of the land site at that time to a certain extent

Sansheng Gongde fish-made pharyngeal tooth fossils were collected from the Lower Oligocene strata in Ulan Bragg, Sansheng Gong, west of Inner Mongolia, outside of the existing grass carp distribution area.
The morphological characteristics show that it does not resemble a herbivorous fish
.
Although its relationship with grass fishes is not yet certain, it is speculated that it may be the carnivorous ancestor of grass fishes
.
This location is close to the northwest corner of the current Yellow River Hetao, which may have been a temperate grassland environment at that time
.

The throat teeth of Liu's first grass carp were collected from the drilling cores of the Upper Oligocene Dongying Formation in the Andi of Dagang Oilfield in eastern China.
The morphology has more similar characteristics to grass carp, indicating that it has more herbivorous habits
.
Its habitat may be milder and moist than in the early Oligocene
.

The emergence of Miocene Xiejia grass carp and Oriental grass carp indicates that these grass carp species are closer to live grass carp
.
Xiejia grass carp is currently only found in the Xiejia Formation in Huangzhong, Qinghai
.
Eastern grass carp was found in multiple strata from the middle to late Miocene, four of which are located in the modern grass carp distribution area
.
Thousands of fossils of the pharyngeal teeth of Eastern grass carp in Sihong, Jiangsu, as well as the abundant pharyngeal teeth of other cyprinids, suggest that there was a large water environment and abundant aquatic plants in it at that time
.

At the same time, considering the mammalian fossils here, it indicates that the climate in this area was relatively warm and humid during the Early Miocene, while the climate during the Liuhe Formation at the top of the Miocene in Shangcao Village, Nanjing, Jiangsu Province gradually became wetter, which is similar to that of Europe and North America.
The increasing arid environment in the Pleistocene is different, which is probably related to the strengthening of the summer monsoon in East Asia
.

The discovery of eastern grass carp in the Tonggur region of Inner Mongolia indicated that there must have been lakes or rivers large enough at that time, and the local climate is very arid today.
The environment is dominated by short grass grasslands, deserts, sand dunes and high alkaline ponds
.

Based on the above content, it can be inferred that the grass carp originated from a carnivorous fish in western China in the early Oligocene.
It was a temperate grassland environment at that time, which is different from the current grass carp habitat
.

Paleoenvironmental significance of grass carp and grass carp fossils

According to the grass carp-like or grass carp fossils found so far, from the late Oligocene to the Miocene, grass carp migrated eastward, spreading to western, eastern and northern China, and the range was much wider than that of existing grass carp
.

Since the Pliocene, along with the uplift of the Qinghai-Tibet Plateau, large rivers flowing eastward into the Pacific were formed in East Asia.
At the same time, the Asian summer monsoon strengthened.
The distribution of grass fishes was finally restricted to the new environment on the east coast of the Pacific and evolved into existing species.
Form the current life and reproduction habits
.

Among the large rivers in eastern China, the Heilongjiang and Yellow River systems share a variety of fish, and grass carp is one of them
.
However, there is no record of grass carp in the Liaohe River system between the two major rivers
.
It is possible that grass carp was once distributed in the Liaohe River
.
At that time, the Nenjiang River was still the upper reaches of the Liaohe River .

In the Quaternary, Changchun City and its surrounding areas between the Nenjiang and Liaohe Rivers were uplifted due to neotectonic movement.
The class was brought to the north of Heilongjiang
.
But when the Liaohe River was separated from the upper Nenjiang River, the water volume and length of the Liaohe River were no longer sufficient for the survival and reproduction of grass carp
.

The evolution of grass fish shows that during the Oligocene, although it was a bit dry and cold near Sanshenggong in western China, it was still warmer than it is today; during the Miocene, the climate in central Inner Mongolia was also warmer and moist than it is today; from the Pliocene on , The climate and water ecological environment in East Asia have become similar to modern times
.

This research was funded by the National Natural Science Foundation of China, the Beijing Municipal Natural Science Foundation, the Guangxi Natural Science Foundation and the Strategic Leading Science and Technology Project of the Chinese Academy of Sciences
.
(Source: China Science News, Cui Xueqin)

Related paper information: https://doi.
org/ 10.
1007/s11430-020-9724-7