The "Kirin Shrimp Zhang" discovered this time has many characteristics of the marine giant predator "Qi Shrimp" and arthropods more than 500 million years ago. Known as the "Kirin" of Cambrian, it was named "Kirin Shrimp Zhang". It is a transitional species, which reveals the mystery of the origin of arthropods. Huang, a researcher at Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, said: "Arthropods are very common. There are centipedes, scorpions, beetles, ants, crabs, spiders, flies, mosquitoes and crayfish around us. These are arthropods. What are their specific characteristics? First of all, it has a hardened epidermis called exoskeleton, then its body is segmented, and its limbs are segmented, not only tentacles, but also appendages in front. It is especially important that the body has segmented steps. "

Life on the earth has experienced a long evolutionary history of about 4 billion years, and it was not until the Cambrian era more than 500 million years ago that complex and diverse life suddenly appeared on the earth. This milestone major life evolution event is called "Cambrian explosion". Since Darwin, the "CAMBRIAN explosion" has been a great scientific mystery that puzzles the scientific community. Darwin specifically mentioned in the Origin of Species that the sudden appearance of CAMBRIAN complex animals is a great challenge to the theory of evolution.

From 65438 to 0984, the "Chengjiang Fauna" discovered in Yunnan by scientists from Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences further highlighted the suddenness of the "Cambrian Explosion" and pushed the "Darwinian Mystery" to a climax. Because the discovery of fossils of Chengjiang fauna shows that almost all modern fauna, including vertebrates, appeared 520 million years ago (figure 1). According to Darwin's theory of evolution, in order to solve the mystery of the CAMBRIAN explosion, scientists need to find the transitional ancestor fossils of animal origin.

Figure 1 Ecological Restoration of Chengjiang Fauna (Yang Dinghua Map)

Among Chengjiang fauna, arthropods have the highest diversity. Huang said: "How did these arthropods evolve from their ancestral types into real arthropods? We don't know, because of the lack of a bridge, the' Kirin shrimp' we discovered today is a transitional type between kiwi shrimp and real arthropods. "

How did arthropods evolve? What did their ancestors look like? This is a big problem in biological evolution, which has puzzled generations of scientists 100 years. Zhu, a researcher at Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, and head of the Cambrian Explosion Research Group, said: "Because arthropods are the most diverse and successful life on our planet, where things come from, we must find a series of transitional evolutionary types. Today, we found that this' Kirin shrimp' actually filled the gap. "

Fig. 2 Kirin shrimp fossils (Photo courtesy of Zeng Han)

What does the "Kirin shrimp" discovered this time look like? The research team conducted a detailed comparative anatomical study of the "Kirin shrimp" fossil, which can restore the shape of the "Kirin shrimp" more than 500 million years ago. It is a rare chimeric animal. Zeng Han, an assistant researcher at Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences and the first author of the paper, said: "Kirin shrimp has more than 20 knots, each with a pair of paddle appendages for swimming and a pair of legs and limbs for walking. Its head is like a helmet, and there are five eyes in front of its head, which shows that it should have keen vision, and a pair of appendages covered with small thorns like claws protrude from the lower part of its head. It has many swimming legs, which means it can swim very fast. It integrates the body, appendages and head shells of real arthropods, as well as other predatory appendages, as well as the five eyes of the Cambrian monster Obabin sea scorpion. "

Based on the research data accumulated for many years, combined with the unique chimeric morphology and evolutionary biology analysis of "Kirin shrimp", the research team demonstrated the homology between Kiki shrimp and the first pair of appendages of arthropods. The results show that the evolutionary position of "Kirin shrimp" is between Kiki shrimp and other arthropods, and it is located in the root of arthropods (Figure 4).

Fig. 3 Restoration map of Kirin shrimp (drawn by Sun Jie)

Fig. 4 A new model of arthropod origin and early evolution revealed by Kirin shrimp (drawing by Zeng Han)

Zeng Han said: "In the process of our submission, international colleagues gave very positive comments. They said:' This perfect and unexpected transitional animal fills a knowledge gap in the evolutionary history of arthropods'. It has set an important transition link in the evolution of arthropods, covering several key forms and innovative origins of arthropods, and at the same time solving the controversial issue of homology of early arthropods. "

"Kirin shrimp" represents an important transitional fossil predicted by Darwin's theory of evolution. It builds a bridge between exotic shrimp and the evolution of real arthropods, fills a key missing link in the origin of arthropods, and adds a powerful fossil evidence to the theory of biological evolution. For many years, Zhao, a researcher at Nanjing Institute of Geology and Paleontology of Chinese Academy of Sciences and the stationmaster of Chengjiang Paleontology Research Station, said: "Because we can really talk about science only if we have a good theory of evolution. Because you have the idea of evolution, you will care about the changes of things around you, and you will constantly analyze everything around us, animals, plants and everything, so why should we engage in paleontology? This is also one of our biggest popular science goals and objectives. "

Zhan, director of Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, said that the study of Chengjiang fauna in China will continue. Zhan said: "China has advantages in this respect, and the party group of the research institute also attaches great importance to this work. We also have such strength. It can be expected that we will continue to make new breakthroughs. "