Scientists from Northwest University in Xi'an and Northwest University in Shaanxi Xi'an discover the importance of Chengjiang fauna in explaining the evolution of animals from exceptionally preserved fossils.
Research on life before us came into existence is through the recovery of fossils from various sites across the world. The Chengjiang lagerstatte in Yunnan Province, China, is one such unique site containing very well-preserved fossils also known as "Chengjiang fauna", which include soft-bodied animals that normally do not get fossilized.
Most of these fossils are 520 to 518 million years old, spanning a part of the Cambrian period when life on earth broke out in diversity, leading to a huge increase in number of species this phenomenon is called the "Cambrian explosion." In a new study, two scientists who spent many years digging deeper into this field, including Dr Shu Degan from Northwest University in Xi'an and Dr Han Jian from Northwest University in Shaanxi Xi'an, presented an overview of their research on the Chengjiang fauna and emphasized its significance. These findings, published inEarth Science Frontiers, include significant contributions from Chinese palaeontologists, including Dr Shu's group, in collaboration with other international scientists.
The research spanned three decades, each decade bringing important developments. The first decade, from 1984 to 1994, led to important findings on basal animals such as sponges and jellyfish, and the subkingdom Protostomia. In the second decade, from 1995 to 2005, scientists including Professor Shu's team continued to discover newer animal groups, the most significant being deuterostomes which are a large group of animals that includes humans. In the third stage, from 2005 to present day, the Chinese teams continued to add new groups to the animal tree and dug deeper into the relationships between the formation of the tree and the multi-episodic Cambrian explosion. This paved the way for not only the formulation of a three-part phylogenetic tree of early animals but also the hypothesis that the Cambrian explosion occurred in three episodes. The evolution and diversification of basal animals, followed by protostomes, and finally deuterostomes, thus forming the basis of all forms of animal life today.
Dr Shu commented on the importance of the Chengjiang fauna saying, “Today, many people still believe in creationism, and a common argument that they use is an incomplete fossil record. We feel that filling the gaps in the evolutionary tree with transitional forms, such as those found at Chengjiang and other sites, will help us to gradually dispel misinformation about the theory of evolution, especially when we consider the question of how humans came to be. In essence, we can trace the origins of all extant animals, including us, to ancestors in the Cambrian.”
In particular, Dr Shu points to the discovery of seminal fossils that demonstrate the early forms of our basic organs evolved during the Cambrian explosion. These include the mouth, brain, heart, and vertebrae. It is through comparisons of Chengjiang fossils from the Cambrian period with those from the Precambrian (before Cambrian) period that researchers realized that Precambrian life did not have these basic organs. This revealed the importance of Chengjiang as a reservoir of fossilized soft body parts, such as the nervous system.
In fact, some specimens have such well-preserved nervous systems that scientists could use them to infer how certain species behaved, working from the idea that a complex nervous system implies complex behaviours. This incredible insight offered to us by the Chengjiang lagerstatte provides direct evidence explaining the gradual evolution in the animal kingdom.
“As a compelling testimony of Darwinian theory, the Chengjiang fossils have profound scientific and humanistic significance. Our hope is that the fascinating discoveries at this site will help improve scientific literacy in the public, while also providing new generations of scientists with a framework that they can use to flesh out the animal tree of life.” Concluded Dr Shu.