Friday, March 4, 2011

Walking Cactus

"(An) armoured lobopodian with ten pairs of appendages. Trunk region with nine segments, bearing rows of transverse annulations each with some tubercles. Each region possesses a pair of robust and sclerotized spiny appendages with primary articulation. Anterior is extended, probably forming a proboscis. Posterior region bears a protrusion."

That's the description of a new species found in China and described in the journal Nature last week. The species name is Diania cactiformis, the genus name referring to the Chinese province of Yunnan and the species epithet refering to it's cactus shape. Since, it has garnered the nickname the "walking cactus." It belongs to the group Lobopodia, a now extinct group consisting of small, segmented animals dating back to the early Cambrian. The dorsal armored or sclerotized plates are characteristic of this group. This group of organisms resembles velvet worms (Onychophorans) which are terrestrial worms with legs.

The new species was nicknamed the "walking cactus" because of its many appendages and spiny appearance. The specimen dates from around 500 million years ago, is about 6 centimeters (2.4 inches) long, and has the long worm-like body characteristic of lobopodians. What makes this creature unique is its hardened, jointed legs. These joints are important because they provide a link between lobopodians and arthorpods. Sure missing links are always great to find, but in this case what makes this link so significant? Well, the group Arthropoda contains more than 80% of all known living animal species, we're talking all insects, crustaceans, etc. This newly described link gives insight into how this group evolved. For example, the hardened surfaces of the legs of D. cactiformis imply that arthropods developed hardened limbs before hardened bodies, effectively the first step in evolving the body plan from soft-bodied to an articulated exoskeleton.

The Field Museum in Chicago have imagined it to move something like this:

Read more and see pictures in the paper:
Liu, Jianni, et al. (2011) An armoured Cambrian lobopodian from China with arthopod-like appendages. Nature: 470, 526-530. (DOI: 10.1038/nature09704)

And some story links:
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