Fossil 'Walking Cactus' May Be Missing Link Between Worms and Arthropods

Sporting 10 pairs of partially-jointed legs and displaying an overall prickly countenance, a bizarre creature dubbed Diania Cactiformis roamed the seafloor in what is now China's Yunnan province 520 million years ago. Though only 6 cm (2.4”) long, the so-called “walking cactus” represented a step up from soft-bodied, legless worms and might just be the missing link between worms and arthropods.  

Chinese paleontologists from Northwest University in Xi'an discovered the ancient creature's remains in 2006 while exploring the fossil-rich county of Chengjiang, in southwest China's Yunnan Province. Diania Cactiformis seems to be a member of the Lobopodia, a long-extinct group of animals outwardly resembling worms with legs. Where the fossil differs from its Lobopod brethren lies in its spiny legs, which appear to have hardened surfaces.

Dr. Liu Jianni, leader of the research team from Northwest University, has just published a thesis titled “An armored Cambrian lobopodian from China with arthropod-like appendages” in the latest issue of Nature. The creature's importance is reflected in its being chosen to appear on the respected science journal's front cover (left).

Diania Cactiformis may have stood tall among the worms and worm-like creatures of its time, but it also holds an important place in the ancestry of arthropods, a group of animals that comprises more than 80 percent of all known living animal species.

Its advantage was its legs, and although the “walking cactus” and its immediate descendants faded into extinction, the stiffened and spiked legs it pioneered gave its ancient arthropod relatives an immense advantage over their predecessors.

“With these appendages, arthropods were able to run faster, jump higher and move with more agility,” said Prof. Shu Degan, head of Northwest University's Early Life Institute. “Some appendages even evolved into preying instruments. They helped arthropods become powerful and eventually dominant members of marine, freshwater, land and air ecosystems.” (via Xinhuanet and Nature)