Walking cactus - a new discovery in the evolution of insects


25/02/2011

Fossils of 10-legged worm-like creatures that lived 520 million years ago, could fill the gaps in the history of the evolution of insects, spiders and crustaceans.

The so-called walking cactus belongs to a group of extinct creatures like worms, called the lobopodians, which are supposed to have evolved from arthropods (arthropods). Spiders and other arthropods have segmented bodies and jointed limbs covered with chitinous layer.

Before the opening of a walking cactus, Diania cactiformis, it was thought that all the previously found the remains of worms lobopodian have soft bodies and soft limbs, according to Gianni Liu (Jianni Liu), the principal investigator, who worked in conjunction with the Northwest University in China and the University of Frey in Germany.

"Walking cactus - this is a very important finding, because it is a kind of missing link in the chain of development from the family lobopodians to arthropods," - said the agency Liu LiveScience. Liu and other researchers described the extinct creature based on 3 full and 30 partial fossil remains discovered in Yunnan Province in southern China. The body is a walking cactus is divided into nine segments with 10 pairs of jointed legs, covered with a chitinous cover and measuring about 6 inches in length.

It is still not clear how this worm with legs found their livelihood. Maybe he used his mouth like tube called a proboscis to suck out small particles of dirt, or perhaps he used his echinated front legs for grasping the victim, as suggested by Liu.

The key to the knowledge of the evolution of arthropods today are velvet worms, which are considered the only ones of their relatives. These worms that live in the ground, which at one time confused with slugs, consist almost entirely of soft tissue except for the claws and jaws covered by chitin.

Opening a walking cactus helps to supplement the history of evolution in the period from velvet worms to modern arthropods, which in terms of quantity and variety are the most dominant group of animals on the planet, according to Graham Budd (Graham Budd), poleobiologa professor at the University of Uppsala in Sweden, which was not involved in the study. Professor Graham also believes that a walking cactus is the first and only case in which a creature that is not recognized as an arthropod, has jointed limbs covered with chitin. But he is not convinced that, as the researchers argue, the presence of chitin limbs a walking cactus passed directly down to modern arthropods.

"I’m not convinced that it is - a direct ancestor or a close relative of these arthropods" - he said the agency LiveScience. "I would like to see more visual confirmation because of late continues to occur more and more different materials."

For example, it is possible that moving the cactus has little relevance to modern arthropods, and that his limbs Chitin - the result of years of development. It is also possible that the body primitive arthropods hardened before their limbs. New fossils, particularly from China, have helped clarify the evolutionary history of arthropods, and in the last decade, scientists have more consistency on this story.

Original: LiveScience Translation: M. Potter


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