Wormlike "Walking Cactus" Fossil Found

An artist's reconstruction of the "walking cactus" fossil species.

Illustration by Jianni Liu

Christine Dell'Amore

Published February 23, 2011

Fossils of an ancient, spiny creature dubbed a "walking cactus" have been found in China, a new study says.

The 2.4-inch-long (6-centimeter-long) Diania cactiformis had a worm-like body and ten pairs of armored and likely jointed legs. It would have lived about 500 million years ago during a period of rapid evolution called the Cambrian explosion.

(See "Giant Shrimplike Predator Was a Weakling After All.")

Study leader Jianni Liu discovered the animal during a 2006 excavation in southwestern China's Yunnan Province.

"I was really surprised. I said, What's that strange guy with the soft body with very strong legs?" said Liu, an earth scientist at Northwest University in Xi'an, China.

"When I [went] back and observed it under the microscope, [I realized] it's not only funny, it's very important."

"Walking Cactus" a Clue to Arthropod Evolution?

That's because the newfound animal does not resemble other lobopodians, a primitive group of creatures that flourished in the Cambrian seas.

Although the walking cactus is part of this group, it has robust appendages like those of modern arthropods—joint-limbed animals such as spiders and crustaceans.

(See "Oldest Horseshoe Crab Fossils Found in Canada.")

The walking cactus's unusual limbs strengthen the theory that modern arthropods evolved from lobopodians, the study authors say.

Liu, who found about 30 fossil specimens of the walking cactus, also has some hypotheses for how the creature hunted.

For instance, she suspects D. cactiformis may have sucked up tiny creatures in the mud with its proboscis or used its bristly legs to capture larger prey.

The new walking-cactus fossil is described this week in the journal Nature.