Icon of evolution knocked from its perch, or, wait…how about “arthropod origins, waters around, muddied?”

10 August 2011

Since its original description six months ago, the fossil lobopod Diania has become one of the most celebrated fossils of all time, inspiring everything from elaborate back tattoos to a trendy sportswear line. This beloved “walking cactus” was championed by scientists as a key player in the origin of the most diverse and successful group of living animals. But startling new research suggests that this icon of evolution, this upstart URthropod, was in fact nothing more than an ordinary lobopod with bad skin.

In a series of brief communications published this week in Nature, two groups present revised analyses of the evolutionary relationships among 520 million year old fossil and its presumed relatives including euarthropods (e.g. insects, arachnids and crustaceans), anomalocarididsvelvet worms, water bears, and a variety of extinct stem-arthropods and lobopods, like the bizarre Hallucigenia. The phylogenetic analysis presented with the original description of Diania by Liu and colleagues found the creature to be closely related to a clade that included living arthropods and the outlaw Bavarian folk hero Schinderhannes, this result, coupled with the armored covered legs of Diania, was taken as an important clue to the origins of the stiff, jointed-appendages that are a hallmark of true arthropods.

However, the new reappraisals find Diania several nodes further removed from arthropod origins, mucking around in a polytomy that includes the tardigrades, onychophorans and extinct lobopodians. If these results are correct, it implies that the armored limbs of Diania are likely irrelevant to the origin of hardened jointed legs among arthropods. In a reply, Liu and company concede the tenuous placement of Diania in the family tree of arthropods and their relatives, but provide some additional support for their original interpretation and argue that further study is required to resolve the debate.

Surely, the question of whether Diania is a close relative of arthropods or not will continue to rock the paleontological community for years to come.

Refs:
Mounce, Ross CP and Matthew A Wills (2011) “Phylogenetic position of Diania challenged” Nature 476:E1 doi:10.1038/nature10266

Legg, David A et al. (2011) “Lobopodian phylogeny reanalysed” Nature 476:E1 doi:10.1038/nature10267

Liu, Jianni et al. (2011) “Reply” Nature 476:E1 doi:10.1038/nature10268

2 Responses to “Icon of evolution knocked from its perch, or, wait…how about “arthropod origins, waters around, muddied?””


  1. [Disclaimer: I’m an author of the Mounce & Wills paper]

    Thanks for the blog post. I’m pleased someone is taking note of this. Rebuttals in Nature & Science often don’t get the attention or impact they deserve (don’t believe me? Read this paper for some evidence: http://dx.doi.org/10.1890/ES10-00142.1)

    Just a few minor comments…😉

    When you say “If these results are correct…” There’s no if, or but about it. We’re correct in our assertions (both the Legg et al paper and the Mounce & Wills paper), hence why we’ve had our comments published in Nature.

    Cladistic analyses using parsimony are *exactly* repeatable, replicatable, falsifiable analyses. Given the input data and the settings (as given in the original Liu et al Nature paper) you’ll get exactly the same results as we do. It’s as simple and defensible as 2+3=5

    With the current evidence provided by Liu et al we cannot be sure yet where Diania truly lies on the ‘Tree of Life’ relative to arthropods. We need more evidence, which I’m sure Legg & co will provide in a later fuller paper.

    As for Liu et al’s reply and their attempt to “provide some additional support for their original interpretation” – much of it is rather embarrassing tbh. They’ve just muddied the water rather than admitting the error. I talk a little about this on my twitter feed and my blog post here: http://www.science3point0.com/palphy/2011/08/11/my-1st-peer-review-published-paper/

    The key message from all of this is:

    Don’t uncritically read everything that you find in journals, even in Nature. Peer review doesn’t and will never catch all the significant errors from appearing.

    Thanks again for blogging!

    Ross🙂

  2. Neil Says:

    Hi Ross,

    Wow! Wasn’t expecting an author to stop by. Thanks for your thoughts, and for taking this fairly silly post in stride.

    Since this is semi-satirical it’s probably ill-advised to dig myself in deeper, but you raise some good points so I’ll bite:

    When you say “If these results are correct…” There’s no if, or but about it. We’re correct in our assertions (both the Legg et al paper and the Mounce & Wills paper), hence why we’ve had our comments published in Nature.

    By “if … correct” of course I didn’t mean whether your results were replicable, but rather whether the tree topology conforms to actual evolutionary relationships or not. As you are well aware, with the inclusion of additional taxa or characters, or with a different character coding scheme, the picture could change somewhat.

    Don’t uncritically read everything that you find in journals, even in Nature.

    But you just said the reason your comment was published in Nature was because it was correct!? Just giving you a hard time–but don’t worry I never read anything uncritically. Except Pliny.


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