Major discovery! Chinese scientists found out from feces 35 million years ago that the Earth looked like this

The cover of the 9th issue of the 26th volume of the international academic journal iScience is a healing landscape picture. You can see a quiet pond in the dense forest and grassland, and many crocodiles are resting in the shallow water after eating. But what you don’t know is that the basis of this ecological environment restoration picture comes from a pile of crocodile feces fossils.

Cover of iScience Vol. 26 No. 9. Image source: iScience

This cover paper reports on 55 well-preserved crocodile feces fossils from the late Eocene in northern Vietnam, dating back 35 million years. This discovery established a new genus and species of crocodile feces for the first time. The paper restored the ancient environmental features of the Na Yang Basin through ecological research on the feces fossils , which is the beautiful scenery in the picture above.

Coprolites: A valuable tool for paleontological research

The history of coprolites research actually spans two centuries. From its initial obscurity to the recent multidisciplinary comprehensive research, coprolites have proven to be a valuable tool for paleontological research .

As early as 1829, British geologist and paleontologist William Buckland first studied coprolites and created the term "coprolite", which later became a general term for all coprolites. At that time, Mary Anning, a famous British fossil hunter, noticed that there were often some "small stones" in the abdomen of ichthyosaur fossils. When the small stones were broken, fish bones or fish scale fossils popped out. Mary Anning's observation attracted the attention of William Buckland. After careful research, he proposed in 1829 that these small stones were ichthyosaur coprolites, and the spiral circles on the coprolites were formed in the intestines of ichthyosaurs.

Illustration from William Buckland's 1835 paper on coprolites. Image credit: William Buckland

In fact, this was not the first time that William Buckland noticed coprolites. He had observed hyena coprolites a few years before. In 1822, after investigating mammal fossils in a cave deposit, he wrote: "There are many small balls here, which may be the solid calcium excrement of an animal that feeds on bones... Its shape and appearance are similar to the feces of spotted hyenas." Here I would like to add that William Buckland also had another memorable achievement. In 1824, he studied and named the first valid genus and species of dinosaurs - Megalosaurus.

Nowadays, people are paying more and more attention to the study of coprolites. A series of studies can be conducted on coprolites, including morphology, taphonomy, paleoecology, palynology, biogeochemistry and systematic classification , to reveal the daily behavior, nutritional relationships, feeding characteristics, digestive tract structure and even ancient DNA information of ancient organisms.

A Triassic marine food web reconstructed from coprolites. Image credit: Marie Cueille

The University of Bristol in the UK once studied a large number of coprolites found in the Triassic marine strata in southwest England. They used CT scans to identify the bones and scales of various organisms, and based on this, reconstructed the food web of ancient marine organisms more than 200 million years ago and speculated on the relationship between predators and prey. The research results basically follow our mantra: big fish eat small fish, small fish eat shrimp.

The Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, discovered short-winged beetles and their coprolites in Cretaceous amber. There were large amounts of pollen on the insects and in the coprolites, which were very similar to the pollen of chrysanthemums and roses, indicating that insects have been spreading pollen for higher angiosperms more than 100 million years ago and continue to do so to this day .

How is the ancient ecological environment in which crocodiles lived reconstructed?

The research work of the cover article of "iScience" mentioned at the beginning of the article was completed by the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences and the National Museum of Nature of Vietnam. In the fall of 2018, the joint scientific expedition team conducted field research in the Nayang Basin in Lang Son Province in northern Vietnam. The Nayang Basin is an important fossil site in Southeast Asia, with rich flora and fauna and trace fossils, similar to the Eocene fossil sites in Maoming, Guangdong, China. The expedition team found more than 100 coprolites and fossil materials of various vertebrates in the Nayang Coal Mine.

The scientific expedition team inspected the Nayang coal mine in northern Vietnam. Image source: Wu Feixiang

During the survey, crocodile feces fossils were found buried in situ. The size of the fossils in the picture can be used as a reference to the size of a knife. Image credit: Paul

In subsequent research, the team conducted a series of analyses on the feces, including describing the morphology for classification, establishing the biostratigraphy of coprolites, observing tissue sections, discovering internal substances through CT scans, displaying element peaks through energy spectrum analysis, and reconstructing vegetation appearance through pollen analysis.

Late Eocene crocodile coprolites from the Nayang Basin in Vietnam. Image credit: Paul

Through systematic classification and palynological analysis, the study found that both coprolites and dinosaur footprints are trace fossils. The systematic classification of dinosaur footprints has long been widely recognized, but the systematic classification of coprolites has been stagnant for two main reasons:

Firstly, due to burial and diagenesis, the preservation conditions of coprolites vary. Some feces are crushed into cakes, some are broken into slag, and it is rare to see them preserved in their original state.

Secondly, sometimes the same organism with different feeding habits will produce different forms of feces. This is easy to understand. The food you eat every day is different, and the feces you excrete are also different. With spring, summer, autumn, winter, and festivals, there are at least a dozen styles of feces every year.

The International Commission on Zoological Nomenclature established the naming rules for trace fossils in 1999. Under this rule, this study introduced the nomenclature of crocodile coprolites for the first time and named the new genus and species Crococopros naduongensis, where Crococopros means crocodile coprolites and naduongensis refers to Na Duong, Vietnam, where the coprolites were found.

Coprolites and pollen in the surrounding rocks. Image credit: Paul

The Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences conducted a detailed palynological analysis of the coprolites and surrounding rocks and found that the pollen was extremely rich, with a total of 76 pollen types, including two algae, three ferns, five gymnosperms, and 66 angiosperms.

These pollen can directly help us reconstruct the ancient ecological environment in which crocodiles lived, indicating that more than 30 million years ago, the Nayang Basin in Vietnam had a tropical/subtropical climate, with high and low terrain around it, and the vegetation environment was changing. The higher mountainous areas were subtropical evergreen broad-leaved forests, and the lower lakes and swamps were tropical rainforest environments, with a large number of freshwater algae and aquatic plants in the lakes and swamps, such as water lilies and duckweed.

A complete picture of the Eocene ecological environment restoration in the Nayang Basin, Vietnam. Image source: Paul

The fossil sites of the Nayang Coal Mine also discovered fossils of fish, primates, birds, turtles and other animals. Combined with the vegetation and animal species, scientists and painters can reconstruct the ancient environment and restore the ecological appearance of the Nayang Basin in Vietnam more than 30 million years ago. Thus, a healing picture slowly unfolds: the forest vegetation is thriving, the rivers or lakes are full of water, and the food resources are rich, which is suitable for the reproduction of organisms. Crocodiles, as the top members of the food chain here, thrive here, eat and drink enough, and defecate leisurely.

Planning and production

Produced by Science Popularization China

Author: Zhang Lizhao, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences

Producer丨China Science Expo

Editor: Yinuo