Does New Cambrian Fossil Discovery Shed Light On Arthropod Evolution?

Fossils of a bizarre worm-like animal with legs dubbed the “walking cactus” were found in Chinese Cambrian strata.  Physorg.com claims the discovery sheds “light on the evolution of crabs and spiders.” Paleontologist speculate the organism might have been evolving en route to an arthropod, but the fossil record already evidences that such arthropods already existed in the Cambrian Period.  The organism has been classified as Diania cactiformis by the discoverers from China and Germany, and the research paper is published in Nature.[1]

National Geographic describes Diania cactiformis as being 2.4 inches long (6 cm), having,

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.

Nature’s editorial summary reads,

Jointed limbs in arthropods are a key innovation that facilitated the evolution of the world’s most species-rich animal group. Their ancestors may lie among a group of extinct animals called lobopodians, which looked rather like worms with legs. A newly discovered 520-million-year-old fossil lobopodian from China may be the closest known fossil relative of modern arthropods. A thin worm-like animal, Diania cactiformis is named to reflect its ‘walking cactus’ appearance. The possession of what seem to be the beginnings of robust, jointed and spiny legs suggest that this bizarre animal might be very close to the origins of the arthropods.

The abstract in Nature describes Lobopodians to be “diversified and flourished in the Cambrian seas.”  Resembling ‘worms with legs’, they may have given rise to Onychophora (velvet worms).   The Wikipedia article states, “Lobopodia is a group of poorly understood animals.”  As an extinct group, the origin and classification of Lobopodia will likely always be in dispute.  According to a 2007 study, Origin, diversification, and relationships of Cambrian lobopods, “diversification and relationships of Cambrian lobopods have long been one of the most hotly-debated subjects.”

Velvet Worm

The group, Lobopodia, is in such dispute that taxonomists have yet to classify the group, or designate it as a classification.  According to Encyclopedia.com,   Lobopodia is only a suggested phylum name “to contain the Onychophora as well as the subphyla Tardigrada and Pentastomida.” Onychophora are commonly known as velvet worms, which have functional legs and spit a glue-like slime to incapacitate their prey.  But, to classify Lobopodia in this manner would remove them from the Arthropoda, which is now considered to be monophyletic.

Primitive velvet worms bear a striking similarity to fossilized marine creatures – Lobopodia – from the early Cambrian epoch. Most common in the Southern Hemisphere, these ‘worms with legs’ squirt sticky slime to catch and eat insects.

One of the reasons why the discovery of Diania is obtaining much press coverage is the fact that the Diania cactiformis fossil specimen is a highly unusual organism within a very mysterious  would-be phylum, Lobopodia.  Jianni Liu, the palaeontologist who led the research work stated to the Nature News reporter that up until this discovery, “We did not have a single fossil we could point at and say, ‘This is the first lobopodian with jointed legs’.  Now, with the ‘walking cactus’, we do.”

The Nature article adds that the discovery of D. cactiformis,

provides important insights 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.

In other words, this discovery is just one more unique life form to add to the list of diversity of “body plans” common to the Cambrian explosion. The Cambrian explosion is defined by the sudden simultaneous appearance of all the diverse major phyla known today.  The Cambrian explosion is not evidence in favor of evolution, but an argument against Darwinian gradualism.

Living Velvet Worm On A Leaf

There is an excellent article entitled “The Cambrian Explosion” by Stephen C. Meyer, Marcus Ross, Paul Nelson, and Paul Chien that appears in the volume Darwinism, Design, and Public Education published with Michigan State University Press.  The chapter discusses evidence revealing how the pattern of fossil appearance in the Cambrian period contradicts the predictions or empirical expectations of neo-Darwinism.

Stephen Meyer and his coauthors argue that the fossil record displays several features as a hierarchical top-down pattern of appearance, the morphological isolation of disparate body plans, and a discontinuous increase in information content.  During the Cambrian event, the same article states, “at least nineteen, and as many as thirty-five (of forty total), phyla made their first appearance on earth.” For more on the Cambrian Explosion, there is an excellent video presentation, Evolution’s Dilemma, which is very much worth the view.

D. cactiformisis no more advanced in complexity than other Cambrian organisms, and likewise the “walking cactus” is no less primitive than Cambrian life forms either.  D. cactiformishad the ability to move its jointed, hardened surface, arthropod-like limbs just like the articulated limbs of crustaceans or insects that are alive today.  D. cactiformis was not much different than a modern velvet worm that are alive today, the point being that such a body plan is evidence of design just like all the other Cambrian life forms are.


[1] Liu, Steiner et al, “An armoured Cambrian lobopodian from China with arthropod-like appendages,” Nature 470 (24 February 2011), pp. 526–530, doi:10.1038/nature09704.

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One Response to Does New Cambrian Fossil Discovery Shed Light On Arthropod Evolution?

  1. Denisha says:

    Notnihg I could say would give you undue credit for this story.

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