The "Zhang's Unicorn Shrimp" discovered this time has multiple characteristics of the giant marine predator "Anomalocaris" and arthropods more than 500 million years ago. It is known as the "Crimson Shrimp" of the Cambrian. Kirin", named "Kilin shrimp", it is a transitional species that opens up the mystery of the origin of arthropods. Huang Diying, a researcher at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, said: "Arthropods are very common, such as centipedes, scorpions, beetles, ants, crabs, spiders, flies, mosquitoes, and crayfish around us. These are all arthropods. What are they like? What are its specific characteristics? First of all, it has a hardened epidermis, called an exoskeleton. Then its body is segmented, and its limbs are also segmented. Not only its antennae, but also its front appendages. What’s particularly important is that its body is segmented. ”

Life on earth has experienced a long evolutionary history of about 4 billion years. It was not until the Cambrian era more than 500 million years ago that complex and diverse life suddenly appeared on the earth. This landmark event in the evolution of life is known as the "Cambrian Explosion." Since Darwin, the "Cambrian Explosion" has been a major scientific mystery that has puzzled the scientific community. Darwin specifically mentioned in his "The Origin of Species" that the sudden appearance of complex animals in the Cambrian period was a huge challenge to the theory of evolution.

In 1984, the "Chengjiang Fauna" discovered by scientists from the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences in Yunnan further highlighted the suddenness of the "Cambrian Explosion" and pushed "Darwin's confusion" to the end. Toward the apex. Because fossil discoveries in the Chengjiang fauna show that almost all modern animal categories, 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 transitional ancestral fossils from which animal categories originated.

Figure 1 Ecological restoration of Chengjiang fauna (drawing by Yang Dinghua)

Among the Chengjiang fauna, the most diverse are arthropods. Huang Diying said: "How did these arthropods evolve from their ancestors to true arthropods? We have no way of knowing, because there is a lack of a bridge, so the 'Qilin shrimp' we discovered today is between Anomalocaris and true arthropods. A transitional type between "

How did arthropods evolve? What did their ancestors look like? This is a major problem in biological evolution that has puzzled generations of scientists for more than a hundred years. Zhu Maoyan, a researcher at the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences and head of the Cambrian Explosion Research Group, said: “Because arthropods are the most diverse life forms on our planet and are also the most successful ones, where a thing comes from must be determined. To find a series of transitional types of evolution, the 'unicorn shrimp' we discovered today actually fills the gap."

Figure 2. Unicorn shrimp fossil (photo provided by Zeng Han)

What does the "unicorn shrimp" discovered this time look like? The research team conducted a detailed comparative anatomy study on the "Qilin Shrimp" fossil and was able to restore the shape of the "Qilin Shrimp" more than 500 million years ago. It is a rare chimeric animal. Zeng Han, an assistant researcher at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences and the first author of the paper, said: "The body of the 'Kilin Shrimp' has more than 20 sections, and each section has a pair of swimming paddle-shaped appendages, and a pair of It has legs for walking. Its head is like a helmet. There are 5 eyes at the front of the head, indicating that it should have very keen vision. A pair of claw-like appendages covered with small spines extend from the bottom of the head. limbs, so it should still be a predator. And it has so many swimming legs, indicating that it can swim very fast. It integrates the body, appendages and head shell of a true arthropod, as well as other predatory appendages. There are five eyes of the Cambrian monster Obabin sea scorpion."

The research team based on the research data accumulated over the years, combined with the unique chimeric morphology and evolutionary developmental biology analysis of the "unicorn shrimp". , demonstrated the homology of the first pair of appendages between Anomalocaris and euarthropods. The results show that the evolutionary position of "Qilin Shrimp" is between Anomalocaris and other euarthropods, at the root of euarthropods (Figure 4).

Figure 3: Kirin shrimp restoration map (drawn by Sun Jie)

Figure 4: Kirin shrimp reveals a new model of the origin and early evolution of arthropods (drawn by Zeng Han)

Zeng Han said: "During our submission process, 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 framed It played an important transitional step in the evolution of arthropods, covering the origins of several key shapes and innovations of arthropods, and also 'resolved the controversial issue of homology of the front appendages of the early arthropods' heads."

< p> "Qilin shrimp" represents an important transitional fossil predicted by Darwin's theory of evolution. It builds an intermediate bridge from the evolution of Anomalocaris to true arthropods, fills in the key missing link in the origin of arthropods, and adds a new dimension to the theory of biological evolution. Strong fossil evidence. Zhao Fangchen, a researcher at the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences and director of the Chengjiang Paleontological Research Station, who has been working tirelessly to find many fossils over the years, said: “Only when we explain the theory of evolution well can we really talk about science.

Because you have the idea of ??evolution, you will care about the changes in things around you, and you will constantly analyze all the things, animals, plants, and the connections between all things around us. That is why we engage in paleontology. This is also one of our biggest science popularization purposes and Target. "

Zhan Renbin, director of the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, said that the research on the "Chengjiang Fauna" in Yunnan, my country will continue to be in-depth. Zhan Renbin said: "Our country has advantages in this area, and the party group of the institute is also particularly We also have the power to attach importance to this work, and we can expect that we will continue to make new breakthroughs.

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