The Cretaceous World Reappears? What Discoveries Have Been Made in Shandong's Dinosaur Footprint Fossils?

Produced by: Science Popularization China

Author: Sun Jiafeng and Chen Shuqing (Zhucheng Dinosaur Culture Research Center)

Producer: China Science Expo

Shandong was a paradise for dinosaurs in the Cretaceous period. Zhucheng and Laiyang in the Jiaolai Basin preserve a large number of dinosaur bones and dinosaur egg fossils, most of which are concentrated in the Late Cretaceous. Zhucheng is famous for discovering the world's largest and richest dinosaur fossil group, and Laiyang is one of the earliest and richest areas in the world to discover dinosaur fossils.

Among the Early Cretaceous dinosaur bone fossils, the more famous ones are the first sauropod dinosaur in my country, Panpedus shii, discovered in Mengyin, and a small number of Psittacosaurus fossils discovered in Laiyang. In addition, Shandong also has abundant dinosaur footprint fossils, among which a very spectacular group of dinosaur footprint fossils from the late Early Cretaceous were discovered along the Shandong Yishu Fault Zone (Zhucheng-Junan-Linshu-Tancheng line). The scale is rare in China and abroad, and it can be called a wonder of dinosaur geological relics, with important scientific research value.

1. Dinosaur footprints on the Yishu fault zone

The crust of some places will break due to strong pressure or tension. These breaks are manifested on the surface as faults (or fractures). Faults often do not appear in isolation, but in groups, forming fault zones distributed along a certain direction. The activities of fault zones often lead to the formation of earthquakes, bringing serious disasters to people.

Small faults, large faults can extend for hundreds or even thousands of kilometers

(Image source: geograph)

The Yishu Fault Zone is an extension of the famous "Tanlu Fault Zone" in my country. The part of it in Shandong Province is also called the Yishu Fault Zone, named because it is roughly located between the Yi River and the Shu River. The Yishu Fault Zone is a complex fault zone with a long extension, large scale, deep cutting, and long active time. It was formed in the Proterozoic Era and is still active today. It is an important earthquake zone in my country.

Distribution map of the Tanlu Fault Zone. When it was first discovered, scientists believed that it only stretched from Tancheng, Shandong to Lujiang, Anhui. However, it was later discovered that it stretched for more than 2,400 kilometers in China alone, extending northeast to the Sea of ​​Okhotsk. The Yishu Fault Zone is a section of it in Shandong.

(Image source: Li L, Shen W, Sui S, et al. Crustal thickness beneath the Tanlu fault zone and its tectonic significance based on two-layer H-κ stacking[J]. Earthquake Science, 2021, 34(1): 47-63.)

Field geological surveys have found that at least eight dinosaur footprint groups are preserved in the Dasheng Group of the upper Lower Cretaceous of the Mesozoic Yishu Fault Zone (Late Early Cretaceous), including two dinosaur footprint fossil sites in Zhangzhuhewan Village, Zhucheng and Gozhuang Village, Tangdi in the north of the Yishu Fault Zone, one dinosaur footprint fossil site in Junan in the middle, two dinosaur footprint fossil sites in Linshu in the central and southern parts, and three dinosaur footprint fossil sites in Tancheng-Donghai in the south. There are a total of more than 650 footprints in the Yishu Fault Zone from south to north.

(Image source: Journal of Palaeogeography)

2. Why do we need to study dinosaur footprints?

Because through the study of dinosaur footprint fossils, we can not only obtain information about the physiological structure characteristics and habits of dinosaurs themselves, but also the environmental characteristics of the areas where dinosaurs lived.

Whether dinosaur footprints can be preserved, and how good or bad they are, and how deep or shallow they are, are not only related to the height, weight, and walking speed of the dinosaurs themselves, but are also closely related to the composition of the surface materials, the degree of dryness and wetness, and the viscosity. Usually, footprints left on a layer with high water content, fine grains, and high viscosity are deep, and vice versa; but they cannot be too wet, too fine, or too sticky. If they are too wet or too fine, they may not be preserved and will be immediately washed away by water or collapse or be buried by trampled materials; if they are too sticky, the footprints left behind will be deformed and difficult to identify; but they cannot be too dry, or they will not leave any footprints at all - in short, the preservation conditions of dinosaur footprints are relatively strict, and they need to be just right, not too much or too little.

Secondly, dinosaur footprints should be quickly buried by sediments and formed into rocks through petrification. After that, the crust rises and undergoes differential weathering (which requires that the rock that retains the concave footprints is different from the later covering rock) to expose the footprints and be discovered by people. Surfaces with such conditions generally appear on lakeshores, seashores and river beaches, and therefore often appear together with ripple marks, mud cracks, rain marks, etc.

Ripple marks are a structure left on the surface of rocks by wave movement. We can often see modern ripple marks on rivers, lakes and seashores. The ripple marks preserved now also reflect that the environment here was previously a riverside, lakeside or seaside.

Wave marks preserved in rock formations

(Image source: Wikipedia)

Polygonal cracks, called desiccation cracks (also known as mud cracks), are often seen on muddy sediments on river beaches, lake shores, and seashores. They are caused when the sediments are exposed to the water surface before solidification and are exposed to the sun, causing water evaporation and volume shrinkage. This reflects that the strata are exposed to the water surface and the climate is dry and hot.

Modern mud cracks

(Image source: Wikipedia)

Mud cracks preserved in rock formations

(Image source: Wikipedia)

Rain marks are circular or elliptical depressions created when raindrops fall on the surface of unconsolidated mud or sandy sediments.

Typical dinosaur footprint types in the Lower Cretaceous of the Yishu Fault Zone in Shandong Province

1—Dinosaur footprints, Junan; 2—Sauropod footprints, Tangdi Gezhuang Village, Shiqiaozi Town, Zhucheng; 3—Sauropod footprints, east of Tancheng; 4—Footprints, west of Houdianzi Village, Linshu; 5—Theropod footprints; 6—Ornithopod footprints; 7—Ornithopod footprints; 8—Ornithopod and theropod footprints

(Image source: Journal of Palaeogeography)

Various structures associated with the Lower Cretaceous footprint development section in the Shuhe Rift Zone of Shandong Province

1-4 mud cracks, the origins are Junan Houzuoshan Geopark, Tancheng Malingshan Qingquan Temple, Tancheng Malingshan Qingquan Temple, and Tancheng East; 5-8 wave marks are produced in Tancheng East, Linshu Jishan, Linshu Jishan, and Junan Geopark; 9-biological drilling holes in brown siltstone, the origin is Tancheng East

(Image source: Journal of Palaeogeography)

By analyzing dinosaur footprint fossils and the state of the rock layers in which the fossils are preserved, we can infer the environmental and climatic characteristics of the areas where dinosaurs lived at the time, which can supplement the deficiencies in the study of dinosaur bone fossils. Because dinosaur bone fossils and their stratigraphic sedimentary characteristics reflect the burial environment of dinosaurs after their death, while dinosaur footprint fossils reflect the environment when dinosaurs lived. The two can complement each other and jointly construct the entire process of dinosaurs from survival to death, burial, and rock formation.

The Yishu Fault Zone has many footprint fossil sites, which are widely distributed and have many layers. The number of footprints and the types of dinosaurs that made them are rich. The dinosaur footprints in the Shuhe Fault Zone were produced in the Tianjialou Formation of the Dasheng Group, which is 110 million to 100 million years ago and belongs to the late Early Cretaceous. Dinosaur footprints are generally concave impressions, and the makers are mainly sauropods, followed by ornithopods and theropods. The footprints are mostly preserved in the fine sand-sandstone sediment layer with sedimentary structures such as ripples, mud cracks, and rain marks, indicating that the environment of each footprint site was a shallow lake beach or delta front at that time. This place is sometimes flooded and sometimes exposed to the water. Dinosaurs left a large number of footprints on the shore sediments, and the water flow also left ripples on the shore sediments. When the water receded, the footprints and ripples formed before were exposed to the surface, dried and consolidated, and mud cracks formed on the surface of the shore sediments. When the water rose again, the dried footprints, mud cracks and ripples were covered and preserved by new sediments carried by water (the water dynamics cannot be very strong), and then entered the diagenesis stage, and were finally discovered by us after hundreds of millions of years.

In addition, we can also infer the body structure and behavioral characteristics of dinosaurs from these dinosaur footprints . When a dinosaur walks, the distance between two adjacent footprints is called a "single step"; the distance between adjacent footprints of the same foot is called a "complex step"; a series of continuous footprints is called a "track". There are 21 giant tracks consisting of giant sauropod footprints in the north of Tancheng. The diameter of a single footprint is nearly 100 cm (a* in the figure below), which may be second only to the largest sauropod footprint fossil in China in the Lower Cretaceous estuary group in Yanguoxia, southwest of Lanzhou. If the size of the dinosaur that made the tracks is restored based on the calculation that the hip height is equal to 4 times the foot diameter, then the dinosaur that made the tracks is at least 4 meters tall. Based on the ratio of hip height to body length of about 1:4, the body length of the dinosaur can be obtained to be about 16 meters.

The sauropod footprints in the Yishu fault zone vary in size, with the largest hind foot diameter found being nearly 100 cm (Tancheng) and the smallest not exceeding 33 cm; however, the ornithopod footprints vary little, with lengths generally ranging from 30 to 30 cm. The ratio of the stride length to hip height of dinosaur footprints (i.e., the ratio of stride length SL to hip height h, SL/h) can be used to calculate the walking speed of dinosaurs and indicate the walking state of dinosaurs (SL/h < 2.0 for slow walking, 2.0 < SL/h < 2.9 for trotting, and SL/h > 2.9 for running. After calculating the footprint data of the Dasheng Group in the Shuhe Rift Zone based on this method and principle, it was found that the dinosaurs that made the footprints were mostly in a walking state, and it was inferred that these dinosaurs that made the footprints were in a habitat.

Three sauropod dinosaur tracks (a, b, c). Column a may be the second largest sauropod track in China, located in the North Qingquan Temple of Tancheng.

(Image source: Journal of Palaeogeography)

3. Why are dinosaur footprints distributed along the Yishu fault zone?

Why are so many dinosaur footprint fossils distributed along the Yishu Fault Zone? Geological data show that since the late Early Cretaceous, the base of the Yishu Fault Zone has been strongly stretched and faulted, forming a lake surrounded by hills. The lake area is the largest period. The area along the fault zone is a long lakeshore , surrounded by open lake plains, with lush vegetation and a suitable climate. Various creatures, including dinosaurs, live here. The discovery of a large number of dinosaur footprints also confirms that the ecosystem along the Yishu Fault Zone in the late Early Cretaceous was excellent and particularly suitable for dinosaurs to survive, so there are many dinosaur footprint fossil sites distributed along the Yishu Fault Zone.

(Image source: Journal of Palaeogeography)

The multiple Early Cretaceous footprint fossil sites in Shandong provide conditions and important new materials for studying the survival evolution, paleoecology and paleoenvironment of the Early Cretaceous dinosaur fauna in eastern China. The Cretaceous is a period when the dinosaur fauna gradually radiated, and it is also an important period for the origin and radiation of the living fauna.

In recent years, scientists have conducted extensive research on the Cretaceous terrestrial biota of East Asia, especially the Early Cretaceous Jehol Biota. The fossils of hairy dinosaurs, mammals, pterosaurs, primitive birds, fish, insects and early angiosperms found in the Early Cretaceous Jehol Biota are all based on physical fossils such as bones, while the corresponding footprint fossils are relatively rare. For example, only two cases were found in the Yixian Formation in northern Hebei and western Liaoning. In contrast, there are fewer Early Cretaceous dinosaur bone fossils in Shandong Province in eastern China, with only a small number of Psittacosaurus, while there are more dinosaur, pterosaur and bird footprints, which are mainly found in the lower Laiyang Group and the upper Dasheng Group of the Lower Cretaceous. The large number of dinosaur bone and egg fossils preserved in Shandong are mostly concentrated in the Late Cretaceous, and the discovery of Early Cretaceous dinosaur footprints makes up for the lack of bone fossils.