2020-11-06

The peculiar”unicorn shrimp” fossil more than 500 million years ago

By yqqlm yqqlm

China Daily, November 5th. On November 5th, the British”Nature” magazine reported a shrimp-like animal fossil discovered by the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences more than 500 million years ago. At that time, the marine giant predator”Odd Shrimp” and arthropods (such as insects, shrimps and crabs) had multiple characteristics, which were known as Cambrian “kylin”, named”Zhang’s unicorn shrimp”, it is a transitional species that opened the mystery of the origin of arthropods. This is another major new scientific discovery in the”Chengjiang Fauna” in Yunnan, my country, which adds empirical evidence to the theory of biological evolution.

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 Earth. This milestone major life evolution event is called”Cambrian Explosion“. Since Darwin, the”Cambrian Explosion” has always been a major scientific puzzle that plagued the scientific community. Darwin specifically mentioned in his”Origin of Species” that the sudden appearance of complex animals in the Cambrian was a huge challenge to the theory of evolution.

In 1984, the”Chengjiang Fauna” discovered by scientists from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences in Yunnan further highlighted the suddenness of the”Cambrian explosion” and pushed the”Darwin’s confusion” To the vertex. Because the discovery of fossils in the Chengjiang fauna shows that, including vertebrates, almost all modern animal phylums 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 the animal phylum origin.

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Picture 1:Ecological restoration of Chengjiang fauna. (Drawing by Yang Dinghua)

Among the Chengjiang fauna, arthropods are the most diverse. Since the Cambrian outbreak, arthropods have been one of the most successful animals on the planet. Arthropods (such as butterflies, crabs, centipedes and spiders) occupy approximately 80%of the species diversity in the animal kingdom today. However, how did arthropods evolve? What did their ancestors look like? This is a major problem in biological evolution, which has plagued generations of scientists for more than 100 years.

Recently, the Cambrian outbreak research team led by researcher Zhu Maoyan found the key fossil”kylin shrimp” in the Chengjiang fauna to answer the”mystery of the origin of arthropods”, in the form of a research paper The latest research results were published in the journal Nature.

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Figure 2:Kirin shrimp fossil (photo courtesy of Zeng Han)

The”unicorn shrimp” discovered this time has obvious characteristics of true arthropods, such as hardened epidermis, Healed head shell, knotty torso, and segmented legs. However, its head is inlaid with the morphological structure of the arthropod ancestor type, including the Cambrian monster-the unique five eyes of the Opabin sea scorpion, and the Cambrian giant predator-the strange shrimp Predatory appendages. Therefore, the”unicorn shrimp” combines the physical characteristics of true arthropods and arthropod ancestors, and is a rare chimeric animal (Figure 2 and Figure 3).

In this study, the research team conducted a detailed comparative anatomical study on the fossil”unicorn shrimp”. Based on the research data accumulated over the years, combined with the unique chimeric morphology and evolutionary developmental biology analysis of the”kylin shrimp”, the homology of the first pair of appendages between the strange shrimp and the true arthropod was demonstrated. The results show that the evolutionary position of the”unicorn shrimp” is between the strange shrimp and other true arthropods, and is located at the root of the true arthropods (Figure 4).

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Figure 3:Restoration map of unicorn shrimp (drawing by Sun Jie)

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Figure 4:New pattern of arthropod origin and early evolution revealed by unicorn shrimp (graphic by Zeng Han)

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The”unicorn shrimp” represents an important transitional fossil predicted by Darwin’s theory of evolution. It bridges the evolution from the strange shrimp to the true arthropod and fills in the key missing link in the origin of arthropods, giving the theory of biological evolution Added a strong fossil evidence.

Source:China Daily Net