Posts Tagged ‘lobopods’

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