2020-11-05

First discovered! A”Shrimp, Shrimp, Shrimp, Shrimp, Shrimp, Shrimp” 500 million years ago

By yqqlm yqqlm

How did the arthropods evolve? What did their ancestors look like? This century-old puzzle of biological evolution may be solved by Chinese scientists.

Recently, the research team of the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences discovered for the first time in the world a shrimp-shaped fossil more than 500 million years ago:it looks strange, has five eyes, and contains giant marine predators< span class=”entity-word” data-gid=”20406305″>The predatory appendages of the strange shrimp, as well as the hardened epidermis of arthropods such as mosquitoes, shrimps and crabs, healed head shells, and knotty Torso and segmented legs.

Because its body is embedded with the morphological characteristics of a variety of animals, just like the auspicious beast in Chinese traditional mythology-unicorn, it was named”Zhang’s unicorn shrimp”.

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Kirin shrimp fossil. Photo courtesy Zeng Han

These unicorn shrimp fossils discovered by Chinese scientists in the Cambrian strata filled the arthropods The key missing link in the process of animal origin will solve the century-old puzzle of the origin of arthropods. On November 5th, Beijing time, the journal Nature published this latest research result.

“This is another major discovery in our study of the Chengjiang fauna. The unicorn shrimp represents an important transitional species predicted by Darwin’s theory of evolution. It serves as an intermediate bridge from the evolution of the strange shrimp to the true arthropod. It adds a strong fossil evidence to the theory of biological evolution.” Researcher Zhu Maoyan, head of the research group of Cambrian Explosion, who published the paper, said .

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The fossil of unicorn shrimp. Photo by Chen Lei, a reporter from Science and Technology Daily

Scientific puzzles of the Cambrian explosion

Life on Earth has gone through a long history of about 4 billion years. Why did it reach the Cambrian more than 500 million years ago? Did complex and diverse life suddenly appear on the earth in the age of epoch? Since Darwin, the”Cambrian Explosion”, a major life evolution event, has always been a major scientific mystery 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 our research institute scientists in Yunnan further highlighted the suddenness of the’Cambrian explosion’ and pushed the’Darwin’s confusion’ to the top.” Researcher Huang Diying, the corresponding author of the paper, explained that because fossil discoveries in the Chengjiang fauna indicate that, including vertebrates, almost all modern animal phyla appeared 520 million years ago. According to Darwin’s theory of evolution, to solve the mystery of the”Cambrian explosion”, scientists need to find transitional ancestor fossils that originated from animal species like Archaeopteryx. ”

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Ecological restoration of Chengjiang fauna. Drawing by Yang Dinghua

Fill the missing link in the origin of arthropods

In Chengjiang fauna, arthropods are the most diverse Animals.

“Since the’Cambrian Explosion’, arthropods have been one of the most successful animals on the planet, and they are also the most abundant animals on the planet today. According to Dr. Zeng Han, the first author of the paper, “arthropods have the characteristics of epidermal sclerosis, body segmentation, and appendage segmentation. They occupy about 80%of the species diversity in the animal kingdom and conquer the’sea, land and air’. The butterflies, crabs, centipedes and spiders we know are all arthropods.”

But the origin of arthropods has always been a mystery, and has puzzled generations of scientists.”The evolutionary relationship between arthropods in the Cambrian is still inconclusive.”Zeng Han said.

“In the Chengjiang fauna, the prawn is the top predator of the Cambrian, with a body length of up to two meters, and is considered to be the ancestor type of arthropods. However, the morphological differences between the strange shrimp and the true arthropod are huge, and there is a difficult evolutionary gap between the two. This gap has become a key missing link in exploring the mystery of the origin of arthropods.”The corresponding author of the paper and researcher Zhao Fangchen, head of the Chengjiang Paleontological Research Station, said.

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The unicorn shrimp is a”four different image” with multiple animal forms.

Introduced by Zeng Han, the research team Six rare shrimp-shaped fossils were found in the Chengjiang Fauna, the largest being 7 cm and the smallest being only 1 cm. The researchers used a variety of technical methods to conduct detailed comparative anatomical studies on the fossils and restore their 500 million years ago Shape.

This animal body has obvious characteristics of true arthropods, such as hardened epidermis, healed head shell, multi-segmented torso and segmented legs. However, its head has another The morphological structure of the arthropod ancestor type is chimerized, including the five eyes unique to the Cambrian monster”Opabin Sea Scorpion” and the predatory appendages of the strange shrimp. Therefore, it combines the true arthropod and the arthropod ancestor The type of physical characteristics is a rare”four-not-like” chimeric animal. It is like a unicorn, hence the name.

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Restoration of unicorn shrimp. Photo courtesy Huang Diying

However To determine where the unicorn shrimp is in the evolutionary process, scientific data analysis and calculation must be done. Zeng Han introduced that they based on the accumulated research data for many years, combined with the unique chimeric morphology and evolutionary development biology of the unicorn shrimp The analysis demonstrated the homology of the first pair of appendages between the strange shrimp and the true arthropods. Through pedigree reconstruction, a new model that reversed the evolution of the early arthropods and the morphological changes of the appendages was calculated. The results showed that the evolution position of the unicorn shrimp It is located between the strange shrimp and other true arthropods, and is located at the root of the true arthropods.

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A new model of arthropod origin and early evolution revealed by unicorn shrimp. Drawing by Zeng Han

Arthropods The missing gaps in the evolution of animals were filled. The reviewer of the research paper believes that “this perfect and unexpected transitional animal fills a knowledge gap in the evolution of arthropods”.

Source :Science and Technology Daily

Science and Technology Daily reporter Chen Lei

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Source:Science and Technology Daily