Walking cactus: An illustration showing the walking cactus; the missing link between lobopodians and arthropods.
Fossils of an extinct creature, dubbed the ‘walking cactus’ – that lived around 500 million years ago, could be arthropods’ lost relative, according to a new Chinese study.
The Diania cactiformis fossil, discovered in southwestern China, sheds light on how arthropods – the group of more than a million invertebrate species that includes insects, spiders and crustaceans – evolved their distinctive jointed legs.
The walking cactus belongs to a group of extinct worm-like creatures called lobopodians, which are thought to have been a relative of today’s velvet worms. However, it is the first species of that group found to have the jointed legs typical of arthropods.
“Scientists have always suspected that arthropods evolved from lobopodians, but until now we didn’t have a single fossil you could point at and say that is the first one with jointed legs. And this is what walking cactus shows,” Nature quoted Liu Jianni, lead researcher and a palaeontologist with Northwest University in China and Free University of Berlin, as saying.
“The walking cactus is important because it could be seen as a missing link from lobopodians to arthropods,” she added.
Measuring around six cm long, D. cactiformis resembles a skinny, soft-bodied worm, similar to the lobopodians, and had 10 pairs of jointed legs, similar to arthropods.
The researchers believe its legs had hardened surfaces, not unlike the tough surfaces of the articulated limbs of crustaceans or insects.
They added that the development of jointed legs was only one of three ‘critical steps’ in the evolution of arthropods from lobopodians.
Meanwhile, palaeontologist Simon Conway Morris of the University of Cambridge said the discovery would shed light into the flourishing of new animal body plans during the period dubbed the Cambrian explosion, the sudden appearance – in geological time – of most major phyla around 530 million years ago.
