Cambrian torch bugs were originally leaf-footed animals that "lost" their legs

Guangming Daily reporter Daniel Zhang

Recently, the internationally renowned academic journal "CurrentBiology" published a scientific paper entitled "A Cambrian Early Tubular Pedodactyl" completed by the Key Laboratory of Paleontology Research of Yunnan University in cooperation with the University of Exeter and the Natural History Museum in London. In the paper, the researchers revealed that the torch worm in the Cambrian "Chengjiang Biota" is actually a leaf-footed animal that lost the legs and limbs of the back of the body in order to adapt to benthic pipe life, which is also the earliest example of the disappearance of tissue and organ adaptive degradation in the evolutionary history of animals.

First discovered and named in 1989 by researcher Hou Xianguang, the exotic torch worm is a rare group of worms in the Cambrian Chengjiang biota, living at the bottom of the ocean 518 million years ago. This class has an elongated worm-like body with 5 pairs of tentacles at the front of the body and an enlarged end of the body. Due to its strange morphology, paleontologists have debated the taxonomic location and evolutionary significance of the species for more than 30 years, with early research suggesting that it was a link animal, a tentacle crown animal, a tongue-shaped animal, or a transitional taxa evolving from a legless ring nerve worm to a leged pan-arthropod. After years of accumulation of fossil specimens, the research team of the Key Laboratory of Paleontology Research in Yunnan Province found a tubular structure preserved with the body of the torch insect in the new fossil specimen, proving that the torch insect is a benthic pipe animal, and the expanded end of its body acts as an anchor to fix the insect body in the tube. At the same time, the researchers also discovered new morphological features such as paired eyes of torch insect heads. Combining these new fossil discoveries and through methods of phylogenetic analysis, researchers have finally unveiled the mystery of torch worms.

According to Hou Xianguang, the torch worm actually belongs to the Cambrian leaf-legged insect family. Leafpods are an extinct group of early worms, commonly known as "worms with legs". Although fossil specimens of leafpods are scarce, they are crucial to understanding the evolutionary history of pan-limbed animals and are inextricably linked to the origin and early evolution of living tardigrades (commonly known as tardigrades), clawed animals (commonly known as velvet worms) and arthropods (such as shrimp crabs, insects, centipedes and spiders). Leaf-legged animals of the family Larrysidae have already possessed a relatively obvious body distinction, mainly manifested in: the legs and limbs in the front of the body are slender and bristled, mainly used for filter feeding; the legs and limbs in the back of the body are short and with claws, mainly used for exercise and climbing. The torch worm, on the other hand, opened up a new mode of life and is the only known leaf-footed animal that operates a benthic pipe dweller. The torch worm mutated during the evolutionary adaptation to the life of the pipe dweller, losing the legs and limbs at the back of the body that were originally used for exercise and climbing, but retaining the legs and limbs at the front of the body for feeding. This is also the earliest example of the disappearance of adaptive degeneration of tissues and organs in animals as we know so far.

The Cambrian period was a critical period for early biodiversity explosions. The study proves that even at such an early stage of animal evolution, examples of the disappearance of adaptive degradation of tissues and organs have occurred. Research further demonstrates the complexity of marine ecosystems during the Cambrian period, while the adaptive radiation of early organisms contributed to the explosion of biodiversity. Richard Howard, a doctoral student of Researcher Ma Xiaoya, is the first author of the paper, and Researcher Ma Xiaoya and Researcher Hou Xianguang are co-corresponding authors.

Guangming Daily (2020-03-23 10th edition)