Chengdu and Chongqing: Dinosaurs are everywhere

The Sichuan Basin lies between Chengdu and Chongqing, which has gone through three stages of development: ocean-lake basin-land basin, so Sichuan and Chongqing are a friendship that has lasted through the ages.

200 million years ago, the Sichuan Basin was home to dinosaurs, with rivers and lakes, hot climate, and lush vegetation. This has been proven by the large number of dinosaur fossils excavated. The dinosaur fossils produced in the Sichuan Basin are not only widely distributed, abundant in number, numerous in categories, and well-preserved, but also have discovered a number of large-scale dinosaur fossil burial groups. It is an important dinosaur fossil producing area in my country and one of the most important paleontological fossil producing areas in the world. Around the Sichuan Basin, from north to south and from west to east, there are places where dinosaurs appeared, with the southwest and east being the most concentrated. Zigong in the southwest is known as the "Dinosaur Nest" and the "Dinosaur Cemetery", while Chongqing in the east is known as the "City Built on the Back of Dinosaurs".

▲About 100 million years ago, thousands of meters thick red rocks were deposited in the Sichuan Basin. This set of red layers constitutes the material basis of the Sichuan Basin. From Chongqing in the east to Chengdu in the west, this red rock can be seen everywhere, and a large number of dinosaur fossils are also buried. Photo by Zhu Xingyu

01

Wandering dinosaurs: dinosaur footprint fossils in Chengdu and Chongqing

If we say that physical dinosaur fossils are not easy to preserve, then the relic fossils left behind by dinosaur activities are even more difficult to preserve and are extremely precious.

There is a new discipline called "paleo-footprint science" that specializes in studying the footprints left by various creatures, including these dinosaur footprints that are hundreds of millions of years old.

You may ask, since we already have dinosaur bone fossils, why do we still need to study its footprints?

In fact, dinosaur footprints play a role that cannot be replaced by bone fossils. Bone fossils only preserve fragmented information about dinosaurs after their death, but the information preserved in footprints can "reproduce" many wonderful moments of dinosaurs in their daily lives!

Since the first discovery of footprint fossils in Guangyuan, Sichuan in the 1940s, the number of named dinosaur footprint fossils in the Sichuan Basin has exceeded two-fifths of the dinosaur footprint fossils discovered in China, making it the region with the most dinosaur footprint fossils in China. These precious trace fossils are of great significance for studying the body shape and structure, living habits, movement patterns of dinosaurs, and the paleogeography and paleoclimate of the Sichuan Basin during the Mesozoic Era.

Of course, all the numbers related to dinosaur footprint fossils are dynamic. As research deepens and new discoveries continue to emerge, these numbers will continue to be updated.

▲Distribution map of important dinosaur footprint fossils in the Sichuan Basin. According to "A Review of Dinosaur Footprint Fossils in the Sichuan Basin" by Ye Yong et al.

According to the description by Ye Yong, a researcher at Zigong Dinosaur Museum, in the article "A Review of Dinosaur Footprint Fossils in the Sichuan Basin", the dinosaur footprint fossils in the Sichuan Basin have three major characteristics:

Earliest: At present, the vast majority of dinosaur footprint fossils discovered in China are from the Jurassic (about 199 million to 145 million years ago) and the Cretaceous (about 145 million to 66 million years ago), while there are relatively few Triassic dinosaur footprints that are older. In the 1980s, the prosauropod dinosaur footprint fossils were discovered in the Xujiahe Formation of the Upper Triassic (about 200 million years ago) in Cifeng Township, Pengzhou City, Sichuan Province. This was the earliest dinosaur footprint fossil discovered in China at that time, filling the gap in the lack of late Triassic dinosaur footprint fossils in China. So far, the Cifeng Pengxian footprint still maintains the record of the earliest dinosaur footprint fossils in China.

Wide distribution: Dinosaur footprint fossils are widely distributed in the Sichuan Basin. In terms of geographical distribution, more than 30 dinosaur footprint fossil sites have been discovered in at least 20 cities (counties) so far. In terms of stratigraphic distribution, dinosaur footprint fossils have been found in strata from the Late Triassic to the Early Jurassic to the Middle Jurassic to the Late Jurassic to the Early Cretaceous. The geological age of dinosaur footprint fossils is continuous and complete.

Rich in variety: According to incomplete statistics, more than 2,000 dinosaur footprint fossils of various types have been discovered in the Sichuan Basin. Although the absolute number is not as high as that of other important dinosaur footprint fossil sites such as Yangshan in Chaoyang, Liaoning and Yanguoxia in Yongjing, Gansu, the variety is far greater than that of other regions.

▲Different types of dinosaurs left distinct footprints. Quoted from Xing Lida's "Early Cretaceous Dinosaurs and Other Quadrupeds in Southwest China"

02Why did dinosaurs fall in love with this place?

Why did the dinosaurs love this place? Why did they leave their footprints and fossil bones here?

The Sichuan Basin went through a complex evolution process to become a dinosaur paradise.

During the Triassic period, since the Sichuan Basin was a unified ancient Bashu Lake, there was not much land above water, and most of the environment was lakeside and swamp. The habitat for terrestrial animals was relatively limited. In addition, the climate was relatively cold and dry, and the vegetation was not particularly lush, so dinosaurs did not develop well.

In the Early Jurassic, the terrain of the Sichuan Basin became flatter and the basin as a whole experienced some ups and downs, but the overall pattern of the sedimentary environment did not change significantly. The northern part of the basin was still dominated by lakeside swamp phases, while the southern part was dominated by shallow lake phases, and the sediments were alternating accumulations of siltstone, shell limestone, and mudstone.

However, since the early Middle Jurassic, the topography of the Sichuan Basin has become more complex, the lake area has shrunk, the southwestern part of the basin is shallower, Zigong and Weiyuan are in a lakeside environment, lakes are scattered all over the place, rivers are crisscrossed, and the entire basin is a river delta, lakeside, and shallow lake environment. The sediments are mainly sandstone and conglomerate, with cross-bedding.

▲Schematic diagram of the ancient landforms of the Sichuan Basin. Cited from the book "Legend of Salt Wells, Hometown of Dinosaurs - Zigong World Geopark" by Li Zhongdong, Xing Lida and Zou Rong

The climate also changed from arid to hot and humid, and the vegetation was very lush, which provided dinosaurs and other animals with a vast living space and abundant food sources. They multiplied and created the first prosperity of the Sichuan Jurassic Dinosaur Dynasty.

In the early Late Jurassic, the basin's geographical environment and climatic conditions were still similar to those of the late Middle Jurassic, and dinosaurs and other associated vertebrates continued to flourish, but the composition of their fauna had undergone tremendous changes.

After the middle of the Late Jurassic, the Sichuan Basin sank as a whole and developed into a large shallow lake again. At the same time, the climate became abnormally dry, vegetation was poorly developed, and the number of dinosaurs and other animals decreased sharply.

Although the basin began to rise again in the late Jurassic, forming a geographical environment similar to the heyday of dinosaurs, the climate was still relatively dry, the vegetation was not lush, and vertebrates could not develop again. Soon, the paleogeographic pattern of the Sichuan Basin changed significantly. The southern, central and eastern parts of the basin rose to highlands, the sedimentary basin continued to shrink to the northwest, and the climate became increasingly dry, thus entering the Cretaceous period.

After the Cretaceous period, the number and population of dinosaurs declined further, and eventually all became extinct at the end of the Cretaceous period (about 65 million years ago).

▲Imaginary picture of ancient Bashu Lake (drawing by Ling Man). Quoted from the book "Legend of Salt Wells, Hometown of Dinosaurs - Zigong World Geopark" by Li Zhongdong, Xing Lida and Zou Rong.

03

Why did the dinosaurs leave their footprints here?

Dinosaur footprint fossils are footprints left behind by dinosaurs when they walked on the surface of unsolidified sediments, which were later preserved through diagenesis to form fossils.

Because they are formed in situ, they best reflect the original sedimentary environment and have a good role in indicating lakeshore and nearshore paleoenvironment.

As a research object of paleontology, dinosaur footprint fossils are also important materials for studying the physiology and living habits of dinosaurs. Therefore, dinosaur footprint fossils are "close-up shots" of animal activities recorded by nature with a natural video recorder, and are footprints of natural history.

▲Imaginary picture of the formation of dinosaur footprints. Quoted from Xing Lida's "Dinosaur Footprints: Tracing the Mysterious Marks of Billions of Years Ago"

The formation and discovery of dinosaur footprint fossils is a low-probability event that meets at least three conditions:

First, the ground where the dinosaurs will pass must be of moderate hardness and softness, so that the dinosaurs can leave footprints after walking and preserve them for a period of time. If it is too hard, the dragon's feet cannot leave footprints. If it is too soft, the footprints cannot be preserved.

Secondly, the dinosaurs were lucky enough to pass by such a place and leave their footprints on the ground with moderate hardness;

Third: Before the footprints are destroyed, they are quickly buried to form fossils.

Of course, more importantly, these footprints buried in the rocks still require the wisdom and luck of modern people to discover them.

▲Schematic diagram of the formation of dinosaur footprints

04

Dragon tracks are everywhere, where dinosaurs walked

Zhaojue: The world's smallest dinosaur footprint

In February 2006, based on clues provided by the Cultural Relics Management Bureau of Zhaojue County, Liu Jian, Li Kui and others from Chengdu University of Technology discovered large dinosaur footprint fossils in Sanbiroga Village, Sanchahe Township, Zhaojue County.

More than 1,000 footprints were found on a mud sandstone surface covering an area of ​​only 1,500 square meters, making it the largest group of dinosaur footprints discovered in Sichuan to date.

Judging from the morphology and movement patterns of the footprints, most of them belong to sauropod dinosaurs, but there are also pterosaurs and theropods.

Since then, more batches of footprints have been discovered in Zhaojue. In 2016, dinosaur footprint fossil research experts from China, the United States and South Korea announced that a batch of dinosaur footprints they had previously discovered in Yangmozu Township, Zhaojue County, Liangshan Prefecture, Sichuan Province, were identified as the smallest dinosaur footprints ever discovered in the world. This type of dinosaur footprint is called Minisauripus and is only about 2 centimeters long.

▲Multiple types of dinosaur footprints found in Zhaojue

Zizhong Dinosaur Footprints

It was discovered in Zengjiayuanba, Niupanshan Village, Jinlijing Town, Zizhong County, Sichuan Province, and was named Niupanshan Shileiosaur Footprint. It is a large carnivorous dinosaur footprint.

There are two tracks, both of which belong to carnivorous dinosaurs. Track 1 has 20 footprints, and the direction of travel is from southeast to northwest. Track 2 has 22 clear footprints, and the direction is slightly curved. In addition to the clear footprints, some tail marks are also preserved.

▲Schematic diagram of the footprints of the Thunder Dragon in Niupan Mountain, Zizhong

Zigong Dinosaur Footprints

As early as 1972, when Professor Ye Junlin of China University of Geosciences (Wuhan) returned to Zigong to visit his relatives, he discovered many small dinosaur footprints on several huge rocks that had collapsed on the cliff behind Dongyue Temple in Hejie, Gongjing District.

These footprints are preserved in the sandstone layer in the middle of the Ma'anshan section of the Ziliujing Formation of the Lower Jurassic. Nearly 300 carnivorous dinosaur footprint fossils are preserved on the rock surface of about 7 square meters.

These dinosaur footprints are very small, generally only 6 to 8 centimeters long, and the largest footprint is only about 15 centimeters long. Most of the footprints were left by bipedal, three-toed theropods with sharp claws.

In later research, Xing Lida discovered that the morphology of these theropod footprints was similar to that of the Diaodon footprints and the Jialing footprints. The former were widely distributed around the world at the same time, while the latter were common in China.

But what is impressive is not the species of these footprints, but the fact that on just a few square meters of rock, these footprints have preserved three different forms, which is probably caused by different ancient ground environments and additional changes.

Not only that, in 2012, Peng Guangzhao from Zigong Dinosaur Museum and Xing Lida from the University of Alberta in Canada also discovered sauropod footprints in the same location.

The footprints of this carnivorous dinosaur and herbivorous dinosaur have greatly enriched the Early Jurassic dinosaur record in Zigong, allowing us to know that a rich group of dinosaurs appeared in Zigong as early as the Early Jurassic, thus greatly making up for the regret that no dinosaur fossils were discovered in the same period.

▲Schematic diagram of the dinosaur footprints in Fushun. Quoted from the book "Legend of Salt Wells, Hometown of Dinosaurs - Zigong World Geopark" by Li Zhongdong, Xing Lida and Zou Rong.

Gulin Dinosaur Footprints

Hanxi Dinosaur Tracks: The Longest Theropod Tracks and Dinosaur Tracks in East Asia

The "Shifengwo" is located in Hanxi Village, Guihua Township, Gulin County. Preliminary statistics show that more than 270 dinosaur footprints have been found on the 300-meter-long sandstone surface, including three types of theropods, sauropods and ornithopods. Among them, theropod footprints are the most, with a total of 7 groups of tracks found.

The longest dinosaur tracks in the world were found near the city of Sucre, Bolivia. The total length of this group of small theropod tracks from the Late Cretaceous is 581 meters. The longest dinosaur tracks in Asia were found in the Upper Jurassic strata in Turkmenistan. This group of large theropod tracks has a total length of 311 meters. The longest dinosaur tracks found in China before were found at the Chabu Sumu Dinosaur Footprint Site in Otog Banner, Inner Mongolia. Thousands of dinosaur footprints were found at the site, including a group of theropod tracks with a total length of about 65 meters. Therefore, this group of 69-meter-long theropod tracks found in Gulin Hanxi has become the longest dinosaur tracks in China and even in East Asia. It is of great significance to the composition and living habits of the early Cretaceous dinosaur fauna in Luzhou area, as well as the paleogeography and paleoecology of this area.

▲Theropod footprint morphology type B at Hanxi footprint site. Outline (A), 3D image (B). Cited from Xing Lida's "Dinosaur and other tetrapod footprints in the Early Cretaceous of Southwest China"

Jiaoyuan dinosaur footprints: rare theropod swimming traces

In May 2009, it was discovered by Chen Yiguang and Tang Jianming, engineers from the 113th Geological Team of the Sichuan Provincial Bureau of Geology and Mineral Resources, at the Heping Machine Brick Factory in the Second Community of Zhongshan Village, Jiaoyuan Township, Gulin County.

The fossil site is located on the dark purple mudstone in the middle section of the Da'anzhai section of the Ziliujing Formation. About 228 dinosaur footprints were counted at the footprint site, forming 10 tracks. Except for 8 footprints of theropods, the rest are sauropods.

The theropod footprints at the Jiaoyuan fossil site are very special, with thin and tapering toe marks and the lack of any traces of plantar pads, similar to classic theropod swimming tracks, of which only one example has been found in China.

▲Distribution map of Jiaoyuan dinosaur fossil sites and their traces

Huangjing Footprints: Filling the gap in the discovery of dinosaur fossils in the Cretaceous period in the Sichuan Basin

On August 25, 2020, after on-site identification and confirmation by experts including Xing Lida, associate professor and young paleontologist at China University of Geosciences (Beijing), a group of very clear and complete dinosaur footprint fossils from the Cretaceous period were discovered in Gulin County.

Peng Guangzhao, a researcher at the Zigong Dinosaur Museum in Sichuan, said that this fills the gap in the discovery of dinosaur fossils in the Cretaceous period in the Sichuan Basin. "Because previously, the Sichuan Basin mainly found skeletal fossils, and there were many from the Jurassic period, but almost no Cretaceous period discoveries.

▲The latest dinosaur footprints discovered in Gulin. Photographed by Cover News reporter Liu Jian and Li Huagang

Dinosaur footprints in Qijiang, Chongqing

In 2003, the Qijiang District Land and Housing Administration Bureau accidentally discovered many mysterious footprints in a rock cavity while investigating geological disasters in Lianhuabaozhai, Laoling Mountain. After investigation and research by experts from home and abroad, it was found that this was the largest group of dinosaur footprints in the Middle Cretaceous period in southwest my country.

The place where the footprints were found is called Lianhuabaozhai, located in a rock cavity in the middle of a cliff. According to research, Lianhuabaozhai was built in the fourth year of Baoyou in the Southern Song Dynasty (1256 AD). It was originally built to avoid and fight against the Mongolian army. We don’t know whether it played a role in the fight against the Yuan Dynasty like Diaoyucheng in Hechuan. But it is also a wonder that dinosaur footprints from hundreds of millions of years ago lived with humans for a long time.

▲Lianhuabao Village where dinosaur footprints were discovered. Photo by Li Zhongdong

The Lianhuabaozhai dinosaur footprint group covers an area of ​​less than 80 square meters and has a total of 9 fossil layers. 656 ancient vertebrate footprints have been discovered

The number of footprint production layers, the large number, the dense distribution, the complete types, the perfect preservation, and the rich biodiversity are extremely rare both at home and abroad.

Here you can find the world's largest ancient bird footprint, China's most perfectly preserved duck-billed dinosaur footprint, and the largest number of pterosaur footprints in China.

In terms of the preservation methods of footprints, five types of dinosaur footprint fossils have been discovered, including concave footprints, convex footprints, phantom footprints, dynamic footprints, and 3D cast footprints. It is rare to see footprints of different preservation methods preserved in the same fossil site, either in China or in the world.

▲Distribution map of footprints at Lianhuabaozhai footprint site. Cited from Xing Lida's "Early Cretaceous Dinosaur and Other Quadruped Footprints in Southwest China"

What’s even more amazing is that on a fossil specimen that is 60 cm long and 40 cm wide, there are 9 dinosaur footprints of different types, different movement directions, and which intersect and overlap with each other.

What are these dinosaurs doing together?

Who did these ancient footprints come from? According to research, there were four types of dinosaurs here: ankylosaurs, sauropods, theropods, and ornithopods.

It is worth mentioning that a large number of ancient bird footprints were found in this area. The consistent direction of these footprints reflects the characteristics of group life. What is even more rare is that these footprints are preserved at the same level as pterosaur footprints. The simultaneous appearance of two competing flying animals provides us with a lot of information about paleoecology.

▲There are 9 footprints on one specimen (3D footprint scan)

References

1. Li Zhongdong, Xing Lida, and Zou Rong, "Legend of Salt Wells, Home of Dinosaurs—Zigong World Geopark", 2015, Planet Map Press;

2. Xing Lida, "Dinosaur and other tetrapod footprints from the Early Cretaceous of Southwest China"

3. Ye Yong et al., "A Review of Research on Dinosaur Footprint Fossils in the Sichuan Basin"