High-resolution microcts reveal mystery of the evolution of Cambrian animal shell breaks

Researchers from the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences have discovered a new type of soft-tongued snail-and-shell edgy snail, a new type of soft-tongued snail from 518 million years ago, in the carbonated rock mezzanine of the Yuji Mountain Group in Yunnan Province. Using high-resolution microCT technology, combined with scanning electron mirror observation, they restored their complete shell-breaking process for the first time, providing important clues to the mystery of the origin and evolution of animal shell-breaking behavior. The findings were published online in the international journal Paleontology.

High-resolution microcts reveal mystery of the evolution of Cambrian animal shell breaks

The external structure of the shell in the period of the broken shell barrel (for illustration by the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences)

动物外壳的出现,是动物演化历史中非常重要的革新事件,它对于塑造身体构型、保护脆弱的软体以及实现生态扩张具有重要意义。但不断生长的壳体也会阻碍动物的运动和消耗更多能量,为了克服这些缺点,一些带壳动物演化出一种特殊的生存策略——断壳,即通过分泌隔板及溶壳物质断掉壳顶部分,但它何时起源又如何演化一直是个谜。

Yin Zongjun, an associate researcher at Nanjing Institute of Geology and Paleontology, said they found that the shell of the broken shell barrel was curved, cross-sectional or sub-circular, and the top of the shell was a neck-like structure. According to the surface structure of the shell, the period of shell break and the period between shell breaks can be identified. Based on the observation of electric mirror, they used high-resolution X-ray 3D non-destructive imaging technology to reconstruct the specimens at different stages of development in the break-shell period, and restored the complete process of the formation of double-layer partitions inside the barrel screw shell, the formation of the outer ring of the shell and the break-off of the shell.”

They calculated that the shell-broken barrel screw had broken its shell at least twice in its lifetime. For the barrel screws of the fiercely competitive Cambrian and at the bottom of the food chain, regular shell breaks can effectively reduce energy loss and improve motor ability, thus avoiding predators, indirectly revealing that the Cambrian outbreak is not only a big explosion of animal body structure, but also a big radiation of animal survival strategy.

Yin Zongjun said that the phenomenon of barrel screw shell break is the earliest fossil record of animal shell break behavior, its complex shell structure and process, and geological history and modern abdominal foot animal shell ingressprocess are not the same, may reflect the difference steaming mechanism behind the gene regulation, indicating that the shell break strategy in different groups independentorigin many times.

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